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Equipment Discussions >> Binoculars

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EdZ
Professor EdZ
*****

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
"BEST OF" the Binocular Forum - Start Here
      #44730 - 01/24/04 07:51 AM

This is a READ ONLY THREAD CONTAINING LINKS TO INFORMATION for novice and expert alike embedded in binocular forum threads that are diamonds in the deep. Here you will find links to threads that all relate in some way to a primary topic. Consider this like the card catalogue in the Library that will direct you to the proper bookshelf. Comments or discussion of the subject topic should be posted back in the original threads.

ABERRATIONS AND DEFICIENCIES
Affect of Eye Pupil on Binocular Aperture
AFOV vs. TFOV and Separations for Measuring
Aperture / Magnification relationship - Exit Pupil

Best binocular overall or in a given price range
Binocular Articles over on the Reviews side of CN
Binocular Deep Magnitude Observing Charts
Binocular Mounts - Tripods - Adapters - Motions - Homemade
BINOCULAR OBSERVING REPORTS AND TARGET LISTS
Binocular Photo Gallery
Binocular Vision Summation - Two Eyes vs One Eye
Binoviewer - Scope - Binocular Equivalents
BOOKS for Binocular Observers

Chromatic Aberration, Triplets, Semi-Apo, Apo
Cleaning Lenses - Binoc Repair Eyeguards - Caps
Coatings
Contrast

Dark Adaptation, Eye Pupils, Lights
Depth of Field and 3D or not 3D!

Edge Performance - Sharpness of Field
Exit Pupils 5mm vs 7mm

Favorite Binoculars in Various Sizes
First Binocular Purchase? Questions?
Fixed Focus Binoculars

GOOD STUFF FOR BEGINNERS
Handheld Binocular Observing
How to Focus Binoculars

If They Look the Same, What Could be Different?
In Pursuit of Cheap Binoculars. What to Expect.

Limiting Magnitude and NELM

MEASURING / TESTING Optical Aspects of Binoculars

Need Binocular COLLIMATING or Repair?

Philosophy and Binocular Ownership by Bill Cook
Polish Binocular Tests and Reviews
POLLS in Binocular Forum - take a poll
PRISMS - BaK 4 vs BK 7 - Roof vs Porro

Resolution and Visual Acuity
Resolution Testing and USAF Res Charts

Surface Brightness of Extended Objects

Telescope, Binocular
Terrestrial Viewing
Testing Binoculars in the Store Before Buying
Twilight Factor - Visibility - Binoc Index

Vintage and Classic Binoculars Discussions
Vintage and Classic Binoculars Discussion (Part 2)

What can be Seen in Various Sizes Binoculars
Writing a Binocular Review

Zoom Binocular Cautions!


ATTENTION: This post is BEST VIEWED IN THREADED MODE (the word FLAT must appear on the upper right flat/threaded button) so you can see the titles of each "Index Card" subject. Once you find your topic enter that post and you will find links to posts related to that subject. There are now over 350 links grouped into about 40 topic index cards. You will waste a lot of time and effort scrolling if you don't first set to threaded mode.


Thanks and Enjoy,
Moderator, edz
Questioning one’s own understanding is probably the hardest question of all.

Edited by Erix (10/24/12 12:16 PM)


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EdZ
Professor EdZ
*****

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
Twilight Factor - Visibility - Binoc Index new [Re: EdZ]
      #44857 - 01/24/04 01:43 PM

What is Twilight Factor?
When looking at specs for binoculars, I see a line item called "Twilight Factor" and it has a number like 16, 18.3, 20.5, etc...
What is this number telling me?

Multiply the magnification by the objective size in millimetres (for example a 12 x 50 = 600)

Then calculate the SQUARE ROOT of this number ( in this case it would be 24.5 )

The HIGHER the Twighlight Factor , in theory at least the BETTER the binocular will perform in POOR or FADING light.

So whilst exit -pupil (arrived at by dividing objective size by magnification --in this example about 4.2) provides increased BRIGHTNESS as it increases, there comes a stage in lighting conditions where increased MAGNIFICATION helps you see things better in darker situations.

Both of these factors, twilight factor and relative brightness are very important --but do not tell the whole story.

ACTUAL brightness and TWILIGHT PERFORMANCE are also affected very much by QUALITY of glass and coatings and optical designs incorporated ( e.g prism types )

So a top quality $1000 10x40 for example may very likely in reality outperform a $100 12x50 in terms of TWILIGHT PERFORMANCE , even though the math would lead you to believe otherwise .

TWILIGHT PERFORMANCE is in my opinion a very important and often under-rated and overlooked factor with binoculars.

Hope this helps - regards -Kenny.

The original thread is at
What is Twilight Factor?


What Is Visibility Index?
Various noted individuals over the years have adopted scales that attempt to represent relative performance of binoculars, based on some ratio of magnification and aperture. Roy Bishop created the Visibility index that is Mag x Aperture. Alan Adler created the Astro Index that is Mag x Sqrt Aperture. EdZ created an index call the Binocular Performance Index (BPI) see CN Reports - Binoculars - How to Understand Binocular Performance (Feb. 2003) that adapted a scale based on the Adler Index (mag x sqrt ap), but then applied factors based on quality (coatings, contrast, polish, light cutoff, etc.). While I have always been a stong supporter of magnifiaction having greatest influence, that can sometimes be very misleading. In my opinion, it is of far greater importance to consider the intended targets and then determine on which (mag or aper) you should place greater emphasis.
However, the brief explanation of how the indices are determined is this:
(For purposes of this discussion, I am assuming all instruments of equal quality. If so, my BPI would give the same comparative result as Adler Index.


Roy Bishop Visiblity Index
20x60 = 1200
15x80 = 1200

Alan Adler Astro Index
20xsqrt60 = 155
15xsqrt80 = 135


this thread discusses the difference between Roy Bishop's Visibility Index and Alan Adler's Binocular Index.
Is aperture king? Does aperture rule?

further discussion on the topic of Indexing
What does the 'Visibility Index' tell you?
this has explanations of when these indices apply and when they do not.

Quote:

this Sky and Tel binocular article ...makes a brief mention of Mr. Bishops article I mentioned. The Observer's Handbook article is much more indepth but contained in the first link is the general idea of his "visibility factor". The second link is his enlarged visibility factor chart from the Sky and Tel article:


http://www2.wwnorton.com/college/astronomy/astro21/sandt/powerbinocs.html


http://www2.wwnorton.com/college/astronomy/astro21/sandt/images/pabin2.gif

Stan





Also see this explanation of Binocular Performance Indexing - BPI
this thread explains it in brief. Following in the footsteps of Bishop and Adler, I developed
Binocular Performance Index, BPI, which is Adler index adjusted for quality.

Alan Adler's article referencing his index can be found here
http://www.weatherman.com/binadler.htm


What the BPI attempts to do is rank binoculars dependant on their performance characteristics. A normal binocular gets no adjustment. The binoculars that exhibit the best attributes, contrast, transmission, lack of aberration, get adjusted up. Binoculars that exhibit some aberrations or are not well corrected for contrast and transmission, get adjusted down.

Premium coatings and full exit pupil light distribution contribute to greater total light transmission. Well corrected lenses, high polished finish, premium baffels and premium coatings and premium eyepieces contribute to lower scatter and high contrast and better resolution. Transmission, Contrast and Resolution (these are related in various ways) are considered attributes that will have an overall additive or deductive contribution to performance. I have arbitrarily assumed to use a factor for two of these that would either contribute or deduct 10% from the overall index. I used Adler Index (mag x sqrt aperture) as the base.

I would rank the BPI of two different binoculars as such:

Nikon SE 12x50
premium coatings, premium baffles, low scatter, high contrast
lack of aberrations, high resolution, high transmission
Bishop = 12 x 50 = 600
Adler = 12 x sqrt 50 = 85
EdZ BPI = 85 +10% for contrast +10% for transmission = 103

Barska 15x70 - Celestron 15x70 - 2002(1st) version Oberwerk 15x70
less than normal coatings, more scatter, lower contrast,
higher than normal aberrations, lower resolution, lower transmission
Bishop = 15 x 70 = 1050
Adler = 15 x sqrt 70 = 125
EdZ BPI = 125 -(minus)10% for contrast -10% for transmission = 100




this article explains it in detail
This study includes explanations of the influence of magnification vs aperture as relates to point sources, (stars in clusters)
How To Understanding Binocular Performance Indexing - a CN Lab Report by EdZ
The testing and methodology that led to develoment of the BPI


Edited by EdZ (02/13/10 09:49 AM)


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EdZ
Professor EdZ
*****

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
AFOV vs. TFOV and Separations for Measuring new [Re: EdZ]
      #44859 - 01/24/04 01:48 PM

The True field of view of the binocular is equal to the Apparent field of view of the eyepiece divided by the magnification. Tfov = Afov / mag

If the Tfov is given as feet at 1000 yds., then Tfov in degrees is (Tfov in feet at 1000yds) / (1000yds x 3 feet per yd) = radians. Then radians x 57.3° per radian = Tfov in degrees.

If the Tfov is given as degrees then the Tfov in feet at 1000 is (Tangent Fov degrees) x 3000 = Fov in feet at 1000 yds.

Binocular Tfov Conversion Tables
given the measure usually printed on your binoc, i.e. 51M at 1000M, look up your field of view here.

But not all binoculars will actually measure what is specified or what is printed on the binocular. In fact many do not. So if you want to know the actual real field of view, measure it in the field by observing a star field.

A useful list for Binocular Observer's is this one with many star fields measured so you can determine the actual True Field of View of your binoculars
How To Measure TFOV Of Binoculars


A more recent discussion on the topic
Apparent FOV, True FOV and Distortion



Nice collection of constellation charts with separations printed on the charts is here
Stellar Separations for Determining Field of View
Chart of Sagitarius
Chart of Leo
Chart of Lyra


Southern Stellar Separations for Determining Field
Chart of Ara
Chart of Musca
Chart of Crux
Chart of Triangulum Australe


Bino FOV Circle templates for a wide selection of charts


Wide-angle binoculars can have narrow Afov eyepieces and Narrow angle binoculars can have wide Afov eyepieces. Except at the narrowest and widest extremes of True field of view, there is no standard rule you can follow.

Some binoculars do not actually measure in the field what is stated for Tfov. Usually the higher cost premium binoculars do measure as stated.

Half of all binoculars I measured have Afov eyepieces between 60° and 65°. They cross a range from narrow to wide True field of view. There are some but few wider eyepieces in use.

What may seem like a narrow 4° field of view at one power would be wide for a 15x or 16x binocular. A 3.5° field of view would be wide for a 20x binocular. On the other hand, a True field of view less than 3.0° seems narrow for ANY binocular.

Some wide Afov eyepieces have excellent performance. Fujinon 16x70 and Oberwerk 15x70 use 64° Afov eyepieces and are sharp to 80%+ Tfov. In comparison, Orion Giant 16x80 uses a much narrower 53° Afov eyepiece and its sharpness characteristics are poor in the outer 40% Tfov.

Some 8x binoculars with a 6.5° field of view may be considered the low end of a wide True field of view for that power binocular. This Tfov is produced with a 52-53° Afov eyepiece, not considered a wide Afov eyepiece. They are sharp to 80% of the True field of view.

Most of the 22x and 25x binoculars on the market are advertised as 3.0° Tfov, but are measuring less than stated. If any 22x or 25x binoculars measure over 3.0° Tfov, they are using eyepieces with Afov approx. 66° to 75°.

You will find that your eyes are not capable of seeing the edges of the filed in eyepieces with an apparent field of view greater than 65° to 70°. Some binoculars advertise 'eyepieces with 80° apparent filed of view.' Well the eye simply cannot use all that at once. The eye has limitations and generally for most people that falls in a range between 60° and 70°.

edz


Apparent Field of View vs. True Field of View
Original thread Confusion with Field of view Differences


Find more info at

Original Thread Apparent FOV vs True FOV


A lengthy explanation of True field of view and Apparent field of view resides in this thread. A selection of the main points pasted here:

Q
I've done a search on FOV and still don't really understand the differences between real TFOV and apparent AFOV.

As a more specific example, Pentax have two roof prism binoculars with specs as follows:
Pentax DCF SP 8x42 (TFOV 6.3 degrees, AFOV 50.4 degrees)
Pentax DCF SP 10x42 (TFOV 6.0 degrees, AFOV 60 degrees)

How does the 10x42 which has a narrower True FOV end up with an Apparent FOV greater than the 8x42? Does this mean a wider visual view through the binoculars (i.e. more sky)?

A
The narrower TFOV means it will see less sky. The apparent AFOV relates to the width of the image generated by the eyepieces. Dividing that by the magnification of the complete instrument yields the true TFOV in terms of actual degrees of arc of sky that will be displayed.


A
In your example the Pentax 8 x 42 has (TFOV)R.F.O.V. of 6.3 degrees

This is more usually described as TRUE field of view(TFOV)

What does 6.3 degrees actually mean ?

One degree can also be expressed as 52.4 feet / 1000 yards
Or as 17.4 metres / 1000 metres

What this means is that if you looked through a binocular with a ( very narrow )one degree TFOV , then at a distance of exactly 1000 yards from where you were standing you would only be able to see a stretch of land or object that was 52.4 feet wide . Anything wider than that would be out of the area which you can see through the binocular.

Or , to convert to metric measures , if you looked through the same binocular , then at a distance of 1000 metres from where you were standing , you would only be able to see a stretch of land or object that measured 17.4 metres wide.

So with a 6.3 degree TFOV , to get the equivalent figure in feet per 1000 yards or in metres per kilometre , you would multiply the figures quoted above by 6.3.

So at 1000 yards you would be able to see a stretch expanding 6.3 x 52.4 which = around 330 feet at 100 yards

In metric , 6.3 x 17.4 = around 109m per 1000m.

The Apparant Field of View simply means the TFOV as described above MULTIPLIED by the MAGNIFICATION.

So a 10 x 50 with a 5 degree TFOV provides a 50 degree AFOV

In this case , knowing the requirement is for a 5 degree TFOV with a 10 x power factor , the lens designer selects what is universally accepted as a 50 degree eyepiece of focal length sufficient to provide 10x magnification within that binocular system.

Thus is why telescope eyepieces are always described by their APPARENT field of view rather than by their TRUE field of view.

For example a plossl e.p usually offers around 50 - 52 degrees AFOV whereas a Televue Nagler can offer as wide as 82 degrees AFOV .

The True fields of views offered by such e.ps in a telescope depends on the focal length of the telescope which in turns affects magnification.

The greater the magnification the narrower the TFOV and the lesser the magnification the wider the TFOV.

A TFOV that would be considered annoyingly narrow for say a 10x binocular( for example 4 degrees TFOV )only really appears so because the AFOV would be only 40 degrees ,arrived at by multiplying 10 x 4 .

However if you had say a 16x binocular with a TFOV of "only" 4 degrees -- the AFOV would be 64 degrees(16 x 4), and as such would appear to be perfectly acceptable because the extra magnification is making up for the narrow field.

What is an "acceptable" AFOV depends very much on individual choice and experience. One can and often does "get used to" a particular AFOV.

Kenny


Field Of View
a discussion inthe eyepiece forum regarding the ability of the eye to scan around the Afov of various eyepieces from 30°Afov to 100°Afov. Also discussed is the range of the eye's ability to see resolution, see clearly, peripheral vision and extent of peripheral movement.



Edited by EdZ (06/10/10 01:28 PM)


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EdZ
Professor EdZ
*****

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
Exit Pupils 5mm vs 7mm new [Re: EdZ]
      #45203 - 01/25/04 07:50 AM

Also read
Affect of Eye Pupil on Binocular Aperture

Exit Pupil is the beam of light exiting out thru the eyepieces. The diameter of that beam can be found by dividing objective diameter size by magnification. Larger Exit Pupil provides increased BRIGHTNESS. But there are some very important points for consideration.

exit pupil 7mm vs 5mm
If you have a 7mm eye pupil then you get all the light from say a 7x50. But if your eye pupil does not get that large, and many don't, then the effective aparture that you are getting out of the binocular is reduced. So, a person with a 6mm eye pupil, when using a 7x50, it actually only getting 7x42. A person with a 5mm eye pupil is getting effectively a 7x35.

7mm exit puplis will provide a much brighter image than a 5mm exit pupil, BUT ONLY IF you have very very dark skies. Then you would have good contrast. But if you have any amount of light pollution, let's say you have mag 5 skies or worse yet mag 4 skies, then that large 7mm exit pupil may work against you. The brighter sky background will be brighter in the binocular with a 7mm exit pupil and it will tend to wash out the contrast for all objects. In this case a 5mm exit pupil might be better.

I would seldom recommend a 7x50 binocular to anyone as it is a specialty binocular far more affected by limitations of exit pupil and sky conditions and in most instances will not perform as it was intended.

I would never recommend a 7mm exit pupil 7x50 as a first astronomy binocular.

edz



Several threads have embedded discussions on exit pupil. Following are discussions and links to the original threads.


One question that a beginner often asks about is exit pupils. There is so much talk about exit pupils that it can be thoroughly mind-boggling. This primer will set you on the right path. When you begin to yearn for more information visit the Best Of link dedicated to exit pupil.
Binocular Primer - An explanation of Exit Pupil, Eye relief and Field of View



Another member asked "I think these (7x50 celestron ultima) are great binoculars...BUT... I find they amplify sky glow or produce it? ... Is this because of the rather large exit pupil(7.1mm)? I don't see this glow in my 15x70's and I'm guessing that it's because of the 4.4mm exit pupil or the higher magnification."
Exit Pupil Affects the Performace of Your Binocular - Make the Right Choice




This discussion took place here several years ago.
Q
Is the difference between a 5mm and 7mm exit pupil really that significant (I've been looking at the Pentax 7x50 PCF WP's)? The 7x50's give a much wider FOV (324ft/1000yds vs. 261ft/1000yds), which I would think is more important for bino star gazing...Am I missing something fundamental here?

A
Generations of binocular designers who have forgotten more about optics than I will ever know can surely not all be wrong or stupid to have designed so many 7 x 50 , 8 x 56 , 9 x 63 , 10 x 70 and 11 x 80 binoculars over so many years.

"Accepted theory" seems to indicate that, generally speaking, people over around 50 years of age have maximum pupil dilation of only around 5mm in darkness. I bravely pronounce that this assumption is somewhat flawed if not complete poppycock. A noted regular contributor to this wonderful site, let alone forum , who is over the age of 50 , has recently had his dilated pupils measured at 7mm --and that not in COMPLETELY dark -adapted circumstances .

There may well be very good arguments that a binocular with an exit pupil as large as 7mm is performing nowhere near it's maximum potential , but that is not to say that the same binocular will not provide a much more "bright, easy and comfortable" image than would the same (aperture) with higher power eyepieces.

Because terms such as "brightness" "ease of view" and "comfort" have no measurable units, they are unlikely to stand-up well in any technical tug of war against the advantages of higher power (and thus smaller exit pupils) that CAN be measured in the very significant and universally accepted and very real properties of contrast and resolution.

So it is the old argument of "swings and roundabouts" , another example of the fact that no matter how good any particular binocular is for any specific intended purpose, there is always a compromise.

When you gain in power you lose in brightness and field of view, when you gain wider fields of view you tend to lose "flatness" -- a desired quality for stargazing.

Another "con" of a large exit pupil is that it amplifies any human eye astigmatism , making it virtually impossible for anyone with such afflictions and NOT wearing glasses or lenses to correct it, to attain "crisp ,sharp, clear" images , which again are terms not to be found in an optics expert's vocabulary but which are more "artistic" terms ... intended to convey just about EVERYTHING desirable about a magnified image.

I happen to prefer very wide fields of view with hand-holdable low power and "easy to see with " 6mm exit pupils, which is why I wouldn't swap my Zeiss 7 x 42 for any binocular in that size or price range.

All this said , I would estimate that 90% of the time a 5mm exit pupil is ENOUGH IF NOT TOO MUCH for binocular astronomy pleasure and performance.

Regards -Kenny.


Tom,
First, if you do not have eye pupils that dilate beyond 5mm, then 7mm exit pupil does you no good. [With the Exception that Larger exit pupils do make it much easier for your eyes to acquire and hold the image]. But if you do have eye pupils that dilate beyond 5mm, then there are applications where the 7mm exit pupil will show greater performance. That is primarily on broad diffuse extended objects. But only if you can get to dark enough skies.

What do you give up to get 7mm exit pupils? Image size. But if the image is broad and diffuse, do you need a larger image scale? Maybe not.

The binocular that would be best for broad diffuse extended objects is not the same binocular that would be best for most other objects. For most everything else, a higher magnification (that produces a smaller exit pupil) provides a larger image and a bit deeper limiting magnitude that allows seeing more. More stars in wide-open clusters, more resolved stars in dense clusters, a little bit more definition in doubles.

All that is probably why many of us own more than one binocular. Kenny even has his terrestrial favorites, I my backpacking favorites.

It's not all in the exit pupil either. A higher contrast, sharper image from a smaller exit pupil can exceed an image from a larger exit pupil if not from an equally high quality binocular.

My 16x70s exceed my 15x70s and my 10x70s.
My 12x50s exceed my 10x50s.

But in either case not in field of view. However, fov can lose some of its relative importance if the image is considerably better.

edz


More Info can be found at:
Original Discussion Embedded in Thread "Nikon 10 X 50 Cf Action Vi Binoculars"


EXIT PUPILS
Q
Are large aperture, low mag binoculars pointless?

It seems that large aperture, low mag. binoculars are wasteful. What is the reason for their creation if the extra aperture serves virtually no purpose?
(Would I be better off using my brother's 15x45 binos... or at least be just as well served by a pair of 11x50's because the other 20mm of aperture are wasted?)... Please explain this to me...

A
Binoculars that provide very large exit pupils are designed with maximum brightness in mind. That is, they will deliver the maximum bright image of faint diffuse objects. This is a benefit when viewing faint diffuse nebula or large comet tails or the extended arms of galaxies like M31, M33 and M101, things of that nature.

For almost all objects other than faint diffuse objects, magnification provides greater benefit. Magnification allows you to see deeper in magnitude, putting more stars in the field. This is a benefit in open clusters and star fields like the M24 star cloud or even scanning the Milky Way.

Magnification also provides larger image scale that allows you to see objects that otherwise would have been too small for the eyes to perceive.

Remember, a larger objective gathers more light, allowing you to see faint extended objects. A larger exit pupil delivers a brighter image to the eye, again helpful for faint extended objects. Magnification is what allows you to see most small detail.

Whether large aperture low power binoculars are the right choice in binoculars depends very much on what you intend to use them for.

edz

More Info can be found at:
Embeded in the Original Thread "Are large aperture, low mag binoculars pointless"


A good point is made here;
There would appear to be a popular misconception , even amongst experienced binocular users , that an exit pupil from a binocular that is greater than the dilation of the human eye -pupil , is completely "wasted".

There are two very good reasons why a binocular benefits from having exit -pupils greater than diameter of the eye pupil.

1.Avoids the necessity for setting the IPD perfectly, and then the need to perfectly center your eyes to the exit pupils.

2. Permits your eyes to swivel in their sockets, without losing the image, as the iris of your eye slides off to one side as you look toward the edge of the field of the binoculars.

However
For a 10x70 binocular with a 7mm exit pupil, if your maximum dilated eye pupil is 6mm, then light gathering thru the binocular will be determined as if deleivered by a 10x6mm eye pupil = 60mm effective aperture.... Resolution will be determined as if delivered by 70mm x (6mmeye pupil/7mm exit pupil) = 60mm lens, same as light gathering. In general, if your eye pupil does not dilate as wide as the exit pupil of the binocular, your eye effectively reduces the aperture of the binocular.

More info can be found at
Original discussion in thread "Relation: aperture-mag when view extended objects"


Edited by EdZ (02/13/10 09:47 AM)


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EdZ
Professor EdZ
*****

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
Zoom Binocular Cautions! new [Re: EdZ]
      #45514 - 01/25/04 08:58 PM

Before you decide to go ahead and purchase a ZOOM binocular, please read this bit of advice:
Noted Repair Shop Caution on Zoom Binoculars

Then you can read these various posts by some owners

Zoom binoculars (at a reasonable power/aperture ratio) would be a wonderful thing to use if some manufacturer could overcome the basic design flaws of zooms: narrow FOV, dim images, and collimation problems.

My Nikon 8-16X40 XL Zoom is the best zoom I've seen, very sharp optics almost to the edge of the 5.2* FOV (wide for a zoom). However, when comparing it back to back with other good quality binoculars at 8X, 10X, and 15X, the XL Zoom is somewhat dimmer. This may be in part due to the smaller exit pupil (e.g., 2.6mm at 15X vs. 4.6mm for a 15X70), but probably mainly due to inherent light loss of the zoom lens since they are also dimmer, though less so, at 8X and 10X.

Despite this flaw, having the ability to "dial up" the right magnification for the object you want to view is a very nice feature. I'm not sure if aspherical lens technology, better coatings, etc. could overcome the inherent design flaws of zoom bins, but if they could be designed as good or even nearly as good as fixed power bins, they would surely be the most popular bins on the market.

Until then, the Nikon XL Zoom is probably the best compromise possible. The new dual power Leica Duovids look very promising, but are very pricey and heavy for handheld use. If anyone has used one of them (8+12X42) or 10+15X50), please post a review. Thanks.

Brock

See the entire discussion at
100x zoom bino's


I have a Nikon 8-16X40 XL Zoom, and it's great for astronomy, particularly from a light polluted site where smaller exit pupils are needed to increase contrast. It's also good for birding/wildlife observation (close focus 15'). Unlike many zooms it has a fairly wide true FOV (5.2*), which translates to a 83* AFOV at 16X. Of course, the exit pupil at 16X is 2.5, so the views are a little dim at the extreme. The best views are between 10 - 14X. The XL Zooms have very sharp multicoated optics, a bit sharper than my nikon 10X35E2, but with a flatter field, and sharp almost to the very edge.

The XL Zoom weighs 30 oz., less than a 10X50 Ultraview

The XL Zooms are discontinued, but a few companies (hotbuys, for example) still sell them for just under $600.

See the entire discussion at
Anybody using zoom binos?


Check out the previous thread on zooms "Anybody using zoom binos?" started by Tom Trusock. I posted comments about my Nikon 8-16X40 XL Zooms.

I've seen other zooms, and didn't like them, always cheap, dim, small FOV, and not sharp. The XLs are the exception to the rule, however, they DO suffer from miscolimation at close focus.

The alternative type of multiple power bin is the Duovid (8 + 12X42) and (10+15X50). They have two powers instead of a whole range. I haven't heard any rave reviews about them yet, but they're fairly new and VERY expensive so not many people probably have them. However, from reading about them, I think they represent a better alternative to zooms.

See the entire discussion at
Barska 12-60 X 70mm Zoom Binos

See also this thread
Zoom Binoculars for less than $150

Note these comments by various posters. The thread link follows.

note that zoom binoculars usually have a lower FOV then fixed magnifactions. They are however very helpful if these will be your main viewing tool.

Generally, zoom binoculars, although they provide a neat feature, are considered inferior to fixed mag binocs. One thing is for sure, if they go out of allignment, they are nearly impossible to get back in, even by the guys in the shops.

I've not tried the 10 -30 x 60s but although the specs may sound quite reasonable there are always severe limitations with field of view with all zooms I've tried.

See the entire discussion at this thread
Yeah, size matters... but what ELSE does?

Barska 12-36X70 zooms (mini-equipment report)


Edited by EdZ (02/13/10 09:46 AM)


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EdZ
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Coatings new [Re: EdZ]
      #45530 - 01/25/04 09:31 PM

PHASE COATING
Phase coating is special coating and is added to the prisms ONLY in roof prism binoculars to PREVENT destructive interference, actually referred to as constructive interference. Since roof prisms may have on surface that is below th angle of total interanl reflection they have one surface covered with a reflective mirror like material. Somewhere along the light path in the prism, the light has the potential to get out-of-phase. Phase coatings are applied to correct this problem. This is intended to act differently than anti-reflection coatings and is intended to improve the performance of the roof prisms. Standard porro prism binoculars do not use phase coating.
Links to articles on Phase Coating


See this thread discussion where Holger Mmerlitz explains phase correction and provides links for further study
Resolution and Phase Correction

All the remaining discussion here will refer to Antireflection (AR) coatings.


ANTIREFLECTION COATING

Coatings are added to porro prisms and lenses to improve the light transmission of the glass. Also they add destructive interference to cancel out the light reflected off the surfaces. This helps eliminate reflectance and ghost images, a desirable result in lenses and roof prisms, improving contrast.

An uncoated lens surface can reflect 4% of the light hitting it. Magnesium Flouride (MgF) single coating can reduce that reflected light to 1.5%. Properly applied multicoatings can reduce that reflectance to 0.5% or 0.25% per lens surface. Improperly applied multicoatings may do no better than, or not even as good as, good single coatings.

A binocular may have as many as 14 lens surfaces. With the exception of extremely high level of performace of some superior coatings, even a properly muticoated binocular can transmit at best only about 93% to 96% of incoming light. The same binocular with all 14 surfaces only single coated with MgF may transmit only 79% of the light.

Coatings are a very important product in the transmission of light. In this age of products, no one should purchase binoculars that have uncoated surfaces.


Color provides no clear indication of the quality of coatings. There are a variety of chemicals used to develop multi-coatings. Pentax SMC coatings appear purple or rose. Orion Ultraview coatings appear blue/green/purple, depending on what angle you look at them. Some Nikon coatings have a yellowish tinge to them. Single layer MgF coatings appear blue and if applied properly can be better than improperly (too thick) applied multi-coatings. Coatings that are applied too thick can appear bright green.

See this discussion for an explanation of the colors you see reflected from the coatings.
Prisms and Coatings - Differences

Generally, plain blue coatings is an indication of a single coated MgF surface. While MgF coatings are not bad, and in some instances may be better than multicoated (poorly applied) surfaces (ie. compared to the very green coatings mentioned below), single coated surfaces do reflect more light, reduce transmission and may cause internal reflections. I see more internal reflections (ghost images) in my single coated MgF binoculars than any other type of multi-coated binocular.

Coatings that have a multi-hue, blue-green, green-purple, blue-purple, purple-rose, purple-amber, can all be indications of properly applied coating. In this case, a comparison of reflections off the coatings may give some indication of reflected light and hence transmitted light. Generally, these are what I see on better binoculars.

Green coatings, especially very green coatings, may be an indication of a misapplication of the coatings during the process. Phil Harrington has been giving this advice for well over a decade. In order for coatings to work properly, they must be a precise thickness. The precision of the thickness of the coatings is measured in nanometers. Coatings that are applied too thick often end up appearing bright green in color. While the coating surface itself may appear to reflect very little light, the coatings are not performing as antireflection coatings were intended to perform. They may in fact be canceling out portions or certain wavelengths of light, allowing less light to get thru.

It is not uncommon at all to compare binoculars and find a pair with bright green coatings that simply cannot see as much light as another pair, which for all intent and purposes should produce the same result, but by virtue of better coatings can see several tenths of a magnitude deeper. Just to get a better understanding of the importance of the small fractions of magnitudes, a gain of 0.75 magnitude is approximately a 100% increase in total light.

Web Article on Coating Colors


A better indicator than color of the quality of antireflection coatings may be any reflections you can see when looking into them. It is difficult to see any reflections at all in Fujinon coatings. Look into the objectives of an Oberwerk BT100 binocular telescope and you will barely see the outline of your head. You will not see any detail in the reflected image of your face. Look into a binocular with lesser quality coatings and you may be able to see your full reflection in color with detail in your face. Any light you can see reflected coming back off the lens is not passing thru the lens. Premium AR coatings should minimize this reflected light.

You can also shine a flashlight into the objective lens of your binocular and you will see 6 or 8 reflections of the flashlight. Although this will not indicate the quality of the coatings, expect at least to see all colored reflections. White reflections may indicate uncoated glass surfaces. (Note - a cemented doublet objective may produce a white reflection as the two surfaces that are cemented together act as continuous glass and need not be coated). In this age of astronomy, no one should be observing with uncoated lenses.

Here's a simple test to compare Coatings from one model to another
Look for reflections in the coatings

Importance and value of coatings

Nikon 12x50SE coatings vs. Fujinon 10x70 FMT-SX

Coatings compared on a dozen different binoculars

Coatings differences on different models of Pentax binoculars



Q
I would make sure (binocular)are fully multicoated (oberwerk calls them broadband coatings: what ... is that!?).
A
As regards "Broadband Coatings" I asked the same question to Kevin at BigBinoculars.com recently and here was his reply :

Astromart Forums: Astro Binoculars
Re: Broadband coatings
Posted by Kevin Busarow on 4/8/2003 3:43:23 PM

Same question came up in the Binocular Astronomy Yahoo group a while back, and here's what I wrote-
======================================================
Broadband is a multilayer coating (5-7 layers) that has minimal reflectivity (.2% to .5%) across a very wide (broad) range (band) of the spectrum (450nm to 750nm). It's simply the best anti-reflection multi-coating the Chinese manufacturers can do with the equipment they have.

Common MgF2 coatings average 1.3% to 1.5% reflectivity across the same range. While the difference in efficiency with better multi-coatings is small, because binoculars have many air-to-glass surfaces, broadband on every surface (fully broadband multi-coated) can significantly improve overall light transmission. There is also a degree of improvement in contrast, as less light is scattered at each surface. You won't find this level of multicoating on the least expensive Chinese binoculars simply because of the time it takes to do the multiple layers. Some Oberwerk models have this level of multicoating now,
and all models will have it as new stock is received.
Kevin Busarow

Read the Manufacturers Explanation of levels of Coatings


see the embedded discussion at this thread
Anybody using zoom binos


While smaller exit pupils will certainly increase contrast, and as an added bonus compensate for eye aberrations, coatings are very important too. Although the 8X32 SE has a larger exit pupil than the 10X35 E2 (4mm vs. 3.5mm), the "superior" coatings help admit more light and hence help provide better contrast. Similarly, the contrast in my 15X70 '03 Oberwerk is better than my 20X80 Burgess though the exit pupil is larger (4.6mm vs. 4mm), because the Obies have better coatings.

See this discussion at the following thread
Performance of 8.5x44 vs 9x63 vs 10x50?

Q
I bought the Oberwerk 15x70 this year. Is their any obvious visual differences between the 2002 and 2003 models? I would like to know for certain if mine are the 2003 model.
A
The most obvious outwardly noticeable difference is in the coatings. The '02 model has only blue coatings on the eyepieces. The '03 model has the same coatings on the eyepieces as it does on the objectives and it gives off a green/purple color.

A
There is a significant difference in the coatings between the Oberwerk 2002 and 2003 models. While I had noted the 02 model has the most reflections off the lenses of various binoculars I was testing at the time, the new 03 model has significantly less reflections off the objective lenses. At the eye lens, the 02 models appears to be single MgF coated and the 03 model seems to have the same multicoating as the objective.

The overall view thru the new 03 model seems to be noticably brighter than the older 02 model. Viewing around the area of the Cygnus Milky Way, there was more and brighter faint star background visible in the new 03 model.

See the entire thread at
Oberwerk 15x70 2002 vs 2003


I check the coatings in my binoculars on the Moon by looking for reflections inside. If there are reflections, then the coatings arn't so great.
See this post for why you may not be able to tell very much about the coatings by Observing internal reflections of the moon


Edited by EdZ (02/13/10 09:45 AM)


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Aperture / Magnification relationship - Exit Pupil new [Re: EdZ]
      #49488 - 02/03/04 09:04 PM

Aperture / Magnification relationship in binocs

Most recently, this discussion took place touching on all aspects of the above mentioned topic. This thread may be best read in it's entirety.

Comment about Exit Pupil Size


Numerous other threads have discussion related to the same topics.

Are large aperture, low mag binoculars pointless?

See the following comments from some of our forum participants:

It seems that large aperture, low mag. binoculars are wasteful. What is the reason for their creation if the extra aperture serves virtually no purpose?
(Would I be better off using my brother's 15x45 binos... or at least be just as well served by a pair of 11x50's because the other 20mm of aperture are wasted?)... Please explain this to me...

I’ve have come to the conclusion that with binoculars, like everything else in life, it all boils down to compromise. From my …experience I’d have to say that large aperture/low mag binocs are most definitely NOT pointless, they just fill another niche. ... it depends on what your going to use them for.

whilst neither low mag nor large aperture binoculars are remotely "pointless" both categories DEFINITELY have their place in the pleasures of astronomy, unless you are viewing from an exceptionally desirable, non light polluted site, then the combination of LARGE (70mm +) AND LOW power (<12x) would seem to make little sense to me.

when you increase the magnification the image gets a little dimmer so if you are looking at some of the larger nebulae in dark skies the 11x is probably more appropriate.

See the complete comments at this location
Are large aperture, low mag binoculars pointless?!


Masking a Binocular Aperture
Does aperture rule in bino land?
masking is one way to see the effects of aperture vs magnification. This post has a discussion related to some of those effects.
Also refer to the article
How to Understand Binocular Performance


Binoculars that provide very large exit pupils (large aperture-low mag) are designed with maximum brightness in mind. That is, they will deliver the maximum bright image of faint diffuse objects. This is a benefit when viewing faint diffuse nebula or large comet tails or the extended arms of galaxies like M31, M33 and M101, things of that nature.

For almost all objects other than faint diffuse objects, magnification provides greater benefit. It allows you to see deeper in magnitude, putting more stars in the field. This is a benefit in open clusters and star fields like the M24 star cloud or even scanning the Milky Way.

Magnification also provides larger image scale that allows you to see objects that otherwise would have been to small for the eyes to perceive.

Most people will argue that the size of the objective lens is what determines the resolution, and yes this is true. But how much of that resolution the eye can see is dependant on how large the resolved image is magnified. Just about every binocular objective size provides more than enough resolution for the eyes. Without sufficient magnification, the eye will not see what has been resolved.

Take an example of an observer with acuity that allows seeing objects as separated when they are magnified to an apparent size of 150 arcseconds. When viewing an object like M36 using 15x binocs, stars that are as close to each other as 10 arcsec will be seen as separate objects. The same observer using 11x binocs will not be able to see stars only 10 arcsec apart as separate objects, they will appear as one. Hence, 11x will not resolve as many stars in M36.

Remember, a larger objective gathers more light, allowing you to see faint extended objects. A larger exit pupil delivers a brighter image to the eye, again helpful for faint extended objects. Magnification is what allows you to see most small detail.

Also, increases in magnification show more stars. If you used 10x, 12x and 15x binoculars on the same star field, you would see 25-50% more stars with the 12x and another 25-50% more again with the 15x. If you tried to get the same star magnitude gains by increasing aperture and keeping power constant, the size increases over 50mm would quickly make the aperture diameter prohibitive.

Whether large aperture low power binoculars are the right choice in binoculars depends very much on what you intend to use them for.


Relation: aperture-mag when view extended objects

In my 15x70mm Binoculars I know that I can see more stars than a smaller pair, but what about things other than stars?

Suppose I'm looking at M42 with my 15x70's. I assume that magnification doesn't matter too much as it's already pretty big, aperture big enough to match the magnification is more important. I will rate the 'brightness' of M42 through this pair of binoculars as 1.

Now suppose I use a pair of 7x50's. I had thought that these couldn't compare to the 15x70mm's, but now I'm not so sure. If I was to look at M42, it would look smaller, but also stand out more, right? I'm only getting half as much light as I was with the 70mm lenses, but I'm also only magnifying it to have an area about 1/4 the area of the 15x70's. So I would give these a brightness rating of 2. Which is twice as good as the 15x70's.

I know that the bigger image scale does make up for the dimmer view somewhat, but how much does this matter?


There's a lot of factors that determine whether an object will stand out more in a lower power larger aperture binocular.

The larger aperture has greater light gathering ability.

Image scale has a lot to do with whether you can see detail in an object or not.

Extended objects, especially faint diffuse objects benefit from greater aperture.

In binoculars, even globular clusters and dense open clusters can be considered extended objects. These will benefit much more from larger image scale provided by magnification.

I've seen the North America nebula with my 15x70s. I've never seen it with my 10x50s. Assume viewing a 1 arcminute square. If you consider the amount of light gathered spread over the area of the magnified image, then the 15x70s vs 10x50s gather 1.96x the light (70x70=4900 vs 50x50=2500, so 4900/2500=1.96) and they spread it over an area 2.25x as large (15x15=225 vs 10x10=100, so 225sqarcmin/100sqarcmin=2.25x). If 1.96x the light is spread over 2.25x the area, you would think the 15x70s would make it more difficult to see, but that is not the case. Larger image scale can sometimes make it easier to see faint light.

edz

Read the full response at this post
Relation: aperture-mag when view extended objects?


EXIT PUPILS

I wanted to test the difference between two perfectly matched binoculars, but with one variable, exit pupil. I tested 16x70 Fujinons and it's twin, the Fujinon 10x70. Not identical twins, but sure from the same family. These two binoculars share exactly the same everything except the eyepieces. So, only power, and hence exit pupil, are different (and fov, but not important here).

Think of the sky as the backdrop in a portrait. Your subject must stand out from the backdrop to be seen. Consider it to be a grey scale. You all understand the affect of dark sky background. Higher magnification in a telescope reduces the extended light of the background until it approaches a completely dark sky, to the point you can no longer see the field stop. Lower magnification with a larger exit pupil delivers more light, not only from your subject, but also from the background. This can be beneficial or detrimental, depends on the condition. Generally, this makes it much more difficult to see the subject, unless you are viewing under very dark skies.

In moderate 4.5-5.5 skies, 10x70s show a background about three or 4 shades brighter on the grey scale than what is delivered by 16x70s. With a 7mm exit pupil, there is so much light coming into the eyes from the extended sky background, it makes it more difficult to see anything and everything. The 16x70s provide such a contrasty view against the darker backdrop, the contrast gain from the higher magnification of the 16x70s was far reaching and unmistakable. These are exactly the same binocular, so the only improvement in grey scale background most definitely comes only from the increase in magnification, and hence a smaller exit pupil.

But on one night, I did get both binocs out under mag6+ skies. Since the sky was already so dark, the backdrop in the 10x70s did not appear so much brighter than the 16x70s. Much more could be seen with the 10x70s in a darker sky than in the bright sky. Faint nebula stood out now that they were being used in their productive element. On this night the difference between the two was not nearly as great. The 16x70s still see more, but on the faintest nebula, the 10x70s did very well.

My point is not to say one is better than the other. For me, in most conditions, the 16x70s will perform better. But those 10x70s, under the darkest skies I can get to, would be just the tool to observe extended objects and deliver that "finishing" light to my eyes. They have their place. But used in the wrong circumstances, they are no match for the right tool.

Every tool has it's purpose.

edz

Exit Pupil, Large or Small


sure...more magnification means more diffusion of the extended object's light, but I'm asking about the explicit relationship between exit pupil and brightness, not magnification and brightness per se. yes, these are related, but they're not the same thing (keep in mind that two different scopes/binos can give you a different exit pupil for the same magnification...or the same exit pupil with different magnifications).

If we were looking at a white diffuse surface with equal instruments except for exit pupil diameters, the one with the larger exit pupils would have a brighter image. One of the big issues with large exit pupils is that under light-polluted skies they transmit the light pollution as well as the celestial objects. The claim is that smaller exit pupils yield more contrast by reducing the impact of the light pollution

In order to determine the brightness of a view through a binocular you not only need to know the exit pupil size, but also the AFoV. A binocular with a larger exit pupil doesn't *always* give more light to the observer.

Well, not according to the official definitions I've read.

AFOV has nothing to do with image brightness. You are confusing the image formed in your eye with the exit pupil. The exit pupil is simply the image of the effective aperture of the system.

How much light a system transmits is related to its effective focal ratio. If you change the magnification of a system, you also change the effective focal ratio. This has nothing to do with spreading light - sky glow has the same luminance value whether you measure a tiny area or a whole slab.

Lets see how this works. We will use telescopes because we can change the eyepice. The OTA has a printed focal ratio. The brightness of the aerial image formed is dictated by the focal ratio of the scope. An eyepiece will be used to make an image we can see - in astrophotography this is known as afocal projection but using a camera rather than an eye.

The effective focal ratio of the system = OTA focal ratio X eyepice projection magnification.

The eyepiece projection magnification = the eye's focal length / eyepiece focal length.

As you can see, the magnification increases as the eyepiece focal length deceases. And with the first equation, the systems focal ratio increases with the magnification. Using shorter focal length eyepieces increases the effective focal ratio of the system and makes darker images. As the focal ratio increases, the exit pupil deceases.


Light output is not controlled by field of view. If I use an eyepiece in my scope that produces a 3mm exit pupil, it doesn't matter if that eyepiece has a 50° Afov or a 68° Afov, the light output is exactly the same. I just get the same light output over a wider area.

So in effect the view is being dimmed by having a wider AFoV? If you were to somehow block off the edge in the 68 degree AFoV so that all I see is 50 degrees I would assume light output is decreased so that it is less than the orginal 50 degree view?

Again, Light output is not controlled by Field of View.

What is "image brightness"? Can anyone give a clear definition?

several links to sites

One definition of "Image Brightness"

The apparent luminance of the image as seen through an optical system. This brightness is determined by the brightness of the object, the transmittance and the diameter of the exit pupil of the system.

Take a specific magnification, say
10. Then in relation to that, the larger objectives (gathering
more light) yield larger exit pupils:

10x30 = 3
10x50 = 5
10x70 = 7

So the brightness is directly expressed by the exit pupil: the
ratio of light-gathering to magnification.

In terms of the brightness, the largest exit pupils can only be
fully used by dark-adapted younger folks on moonless nights
under dark skies, because the sky background is very dark in
that situation. But under moonlight and light pollution, then
having a lower ratio of gathered light in relation to
magnification yields more contrast, which makes fainter stars
easier to see, since the background is darker.

Brightness in Exit Pupil
Why some exit pupils appear brighter than others of equal size.


Ray Diagrams
All the rays from the cone passing thru the objective to the focal point will pass thru the eyepiece. No rays will be lost. The cone of rays from the objective focal point to the eyepiece exit pupil has a different angle cone for every eyepiece. The shape of the cone of rays gets narrower or wider depending on the eyepiece focal length. That's what focal length is all about. Focal length of a lens creates a cone of light with an angle from the apex at the focal length to the base at the lens. A ray diagram showing a cone of light from the focal length of the objective, once the rays pass the focal point, will show rays at the angle of the eyepiece focal length. Of course F obj / F ep = Mag.

Focal length of a lens


Edited by EdZ (02/13/10 09:44 AM)


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Resolution and Visual Acuity new [Re: EdZ]
      #49491 - 02/03/04 09:10 PM

Here's a link to resolution tests that may help put to sleep the many posts on the internet that display data (not listed as test results, just posted as unqualified data) that states to the effect that a 10x binocular can achieve 6 arcseconds resolution or even an 8x binocular that can resolve 4 arcseconds.
Binocular Resolution Testing w/USAF Charts

The amateur astronomer should know the Rayleigh Limit of a lens determines it's resolving limit, however, the resolving limit can only be achieved at magnifications on the order of 25x per inch of aperture. Sure a 50mm lens has a rayleigh Limit of 138/50 = 2.76 arcseconds, but you have no hope of ever seeing that in a binocular.

Also for astonomical use in dark skies (scotoptic light) the human eye is capable of only achieving 2x to 3x less resolution than in daylight (photoptic light). A retailer that is reporting a resolution of 60 arcseconds for the human eye and 3 arcseconds for a 50mm binocular or 6 arcseconds for any 10x binocular is giving grossly misleading information.

Also the amateur should be aware that the USAF Line Pairs Chart is testing resolution in daylight on high contrast line pairs. The results would be much better than anything that could possibly be achieved in astronomical use due to the ability to see certain kinds of resolution (line pars versus point sources) differently. No binocular can reach the same results on point source resolution under dark skies.


Other Resolution Questions

Below is a series of questions and answers that have been culled from various posts here. There are a number of valuable links that will allow you to godd read some important discussion concerning resolution.


Q There's a strong chance that I will be purchasing Oberwerks' 22 x 100 giant binoculars or something very similar. I just want to know if the 22x to 25x magnification found on most giant binocs is enough to resolve globular clusters? and I mean resolve not grainy...

A I would be surprised if 22X binos could resolve globular clusters. I can't resolve stars in even M13 before about 100x with my 8in reflector.

My 150mm refractor needs 200x to resolve M13 to 60 stars. With my 20x80s I cannot resolve any globulars, although I look at a lot and still enjoy the view.

Q These (25x100mm) bino’s have a good solid build. ...M22 had a mottled look, and it was very easy to see that it was a globular cluster even though there was no way of resolving it at 25x.

A For anything less than optimum magnification, resolution delivered is dramatically reduced. ... Your 8x42 BEST binocular may be capable of 10 to 12 arcsec, and a 16x70 Fujinon is capable of about 7 to 8 arcsec, by the best observers. For astronomy, you cannot achieve those results.

A ...as magnification increases we get to resolve easier. For example, an individual with 150 arcsec acuity can use 10x binoculars to resolve a 15 arcsec double star. However, the same person with 150 arcsec acuity would not be able to see a 1" arcsec double resolved if magnified only to 150x. It would take more like 200x or 250x or more. As objects get closer to the Rayleigh limit, resolution becomes far more difficult and a much higher magnification is need.

Resolution of binoculars


Q Being as I struggle to come to terms with measurements such as "arcseconds", I wondered how close to these miniscular measurements comes a top "E" first guitar string ,measuring precisely 0.3 millimetres, being "clearly resolved" through 10 x 50 binoculars from a distance of 100 metres in very unfavourable lighting ?

A 0.6 arcseconds. That would be near the equivalent of seeing the Cassini Division with those binoculars. That falls within the realm defined for extended objects of line shape.

What happens when the thin line you've selected reflects light? Two very important conditions conspire to allow you to see this thin reflective wire.

First, It becomes similar to a long line of point sources. The light from a point source can be seen even if it has imperceptible width.

Second, A lens is not capable of showing any object smaller than it's limit of resolution. What it will do is make anything smaller than the Airy disk appear as the same size as the Airy disk. Your lens has actually fattened up the image of the line...

Resolution and contrast are related. The lower the contrast of the target, the lower the resolution of the optical system. Brighter stars are easier to resolve. Shiney wires are the same. Most resolution tests are done with high-contrast targets not only because they are easier, but also they give better numbers.

Resolving a thin wire



Visual Acuity is a limiting factor in the eye’s ability to achieve resolution and magnification is employed to make an image large enough for the eye to perceive. If your visual acuity is 200 arcseconds, you need 12x mag to see a 17” double or 20x mag to see a 10” double.

Acuity can be measured as the apparent separation results for a range of varying doubles recorded with one or more pieces of equipment. The results will fall into a fairly narrow range. This would be the observer's acuity range.

Measuring visual acuity is not the same as measuring the resolving ability of your instrument. Resolving is the closest components that can be detected. Acuity is the apparent separation results for a range of varying width doubles measured with various equipment, or even measured with one piece of equipment on various targets. It is surprising how the apparent separation results for a variety of doubles will fall into a fairly narrow range. This would be the observer's acuity range.

Humans are not capable of 1 arcmin resultion in astronomical viewing applications. This value represents the absolutely very best vision, (think O'Meara here), observing a black line on a white ground (think the power line example), in the very best optimum lighting conditions (think black line against blue sky on a bright sunny day with no glare).

...any number of publications report tests that show that a better than average human is capable at best of 2 arcmin acuity, ...and normally 3 arcmin or less of resolution when viewing point sources under subdued light conditions (astronomy).

Testing for Visual Acuity

Q Are large aperture binoculars providing greater resolution?

A Most people will argue that the size of the objective lens is what determines the resolution, and yes this is true. But how much of that resolution the eye can see is dependant on how large the resolved image is magnified. Just about every binocular objective size provides more than enough resolution for the eyes. However, without sufficient magnification, the eye will not see what has been resolved.

...even a 50mm (2") objective is capable of resolving two stars 3" apart. But it would be resolved only if you magnified it large enough for the eye to see it. There is not a common fixed power binocular on the market today that will allow you to see the split in a 3" double, even the 25x150s. But if those lowly 50mm binoculars had 60x or 70x magnification you would be able to see that 3" double as split.

This thread discusses some of the reasons for large aperture binocs
Are large aperture, low mag binoculars pointless


Here you will find explanations for some of the terms used to define resolution
Rayleigh Limit / Dawes Limit


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EdZ
Professor EdZ
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Reged: 02/15/02

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Terrestrial Viewing new [Re: EdZ]
      #50125 - 02/05/04 06:23 AM

Do the critical specs/features to look for when buying large binoculars change when the dominant usage will be distant terrestrial viewing, or do the same factors apply as for astronomical observing?

Large binoculars for distant terrestrial objects

...you mentioned looking across considerable expanses of land & water. In the daytime, frequently there is considerable heating or cooling of the air (what the meteorologists call heating-degree or cooling-degree minutes). This in turn causes thermal activity, which causes the kind of shimmering "funhouse effect" to the image that you see in the movies when a scene is filmed in the desert...the higher the magnification, the more pronounced it is. I currently have 4 hi-end binos and a premium scope and do a lot of birding by local lakes. I find that very seldom can I use the really hi-power eyepieces on the scope and often even the stronger binos don't work as well as the lower powered ones when there is several degrees difference between the air temp and that of the water surface, or between air temp at ground level and just up a few meters. Air has to very stable to have good seeing conditions if you're talking about looking at something much over 2-3 miles away and seeing it to best advantage. I can only use the highest power eyepiece on my scope (48x) very seldom and get the kind of image it's capable of producing...usually the lowest pwr ep (24x) will give a cleaner, more usable view with just as much detail, just a smaller image. This is one of the problems of terrestrial viewing vs cosmological....when stargazing you're looking thru much less dense air which isnt as susceptible to thermal currents


additional posts will be added






Edited by EdZ (02/13/10 09:42 AM)


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Edge Performance - Sharpness of Field new [Re: EdZ]
      #50807 - 02/06/04 11:48 AM

In most binoculars, the image deteriorates the further out from the center of the field of view. Some binoculars have special lenses that help alleviate this problem, and some are just better than others. In general the wider the field of view, the more distortions present at the outer edges of the field of view.

There are many threads where a brief comment is made about edge sharpness, but this one thread covers it in detail. Here is a good discussion related to edge performance.

Edge Performance

Also, you must recognize that edge performance, as noted in a concise statement made by Kenny in the thread above, "["Edge performance" is in itself a rather inadequate title to cover what I consider to be an attempt to categorise what could encompass a whole range of possibly quite different and unrelated properties of an optical system.]", can be caused by a number of issues. To understand better the causes, you should also read the Best Of thread titled
Binocular ABERRATIONS AND DEFICIENCIES


Another thread related to the same topic, once again initiated by Kenny J
True ( SHARP ) field of view


See also this table of measured Binocular Field Sharpness for approx 30 binoculars
So often we hear brief reports about new binoculars to the effect, "this binocular is pinpoint sharp from edge to edge", or "I can only see distortion in the outer 5%-10% of the fov". How are we to believe subjective statements that are not supported by accurate measurments? Frankly, I have tested over 35 different binoculars and have found no fixed power binoculars that are sharp edge to edge and I have found only 2 or 3 that do not exhibit undesirable un-sharpness beyond 80-85% out. With well corrected eyepieces in variable power Binocular Telescopes, you can achieve edge to edge sharpness. This table shows results for a standardized means of measuring that sharpness across all brands of binoculars. It eliminates the subjectiveness.

edz

Edited by EdZ (02/13/10 09:41 AM)


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PRISMS - BaK 4 vs BK 7 - Roof vs Porro new [Re: EdZ]
      #50808 - 02/06/04 11:49 AM

The original discussion that took place concerning the glass type used for prisms is buried within a thread where you would never find it. Here is a link to that discussion. Not all posts in the thread relate, so you may have to skip around a bit.

Where to buy now retitled to Bak 7 vs Bak 4

And don't miss this post way at the bottom of the thread
Bak 7 vs Bak 4 when to use


Another thread with some additional comments

Bak6?


This more recent thread (9/05) discusses some of the properties of BaK4 and BK7 glass and why they are (or are not) used for prisms in binoculars.
Prisms and Coatings - Differences


Roof Prisms vs. Porro Prisms
What are the advantages or disadvantages of one over the other, or are the differences just perceived differences? Do the different types of prisms have any affect on Depth of Filed or Stereoscopic vision? This thread begins to discuss the issues. Dut also refer to the Best Of thread on
Depth of Field and 3D or not,3D! for more related to the same topic.


Edited by EdZ (02/13/10 07:24 AM)


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Binocular Mounts - Tripods - Adapters - Motions - Homemade new [Re: EdZ]
      #51289 - 02/07/04 10:17 AM

We don't have a Minireviews post set-up to list mounts, but this thread is as close as it gets. There are over 30 links here to mounts and tripods threads. some of those threads have 3 or 4 or even 10 more links. Many of the posts you will find are much like mini-reviews of the tripods and mounts mentioned. Also included here are some links to full length articles over on the CN Rreports side. This post is your comprehensive index card linking you to Binocular Mounts. edz


A CN Report on Binocular Mounts, Tripods and Mounting Accessories
http://www.cloudynights.com/documents/thoughts.pdf
pick the right tool for the job. Enjoy. edz



And if you just want to know,
"What are the motions of a binocular parallelogram mount?",
then check this out, it explains the 6 degrees of motion.
Binocular Parallelogram Mount Degrees of Movement



Amateur Made Binocular Chairs and Paralellogram Mounts
Probably the single most comprehensive list of links to Amateur Made Binocular Chairs and Paralellogram Mounts (collected from 60-70 locations, and growing) that you are likely to come across anywhere on the internet. This thread includes a good collection of advice based on lessons learned on "How To" make some of these mounts and chairs. Thanks to Craig Simmons for this collection.
Amateur Binocular Mounts


Many times people ask, Why do you always say you can't mount an 8# binocular on a tripod that is rated for 8#. That is because the load rating for tripods is determined with the load weight directly over the tripod head and directly over the tripod column. Furthermore, load ratings are based on cameras with little to no magnification. With binocular viewing, we often have a big load hanging off of one side. That is like a cantilever or an eccentric load. In all things mechanical, it takes a beefier support to hold an eccentric load than it does to take a direct load. Add to that some 10x or 12x or 25x magnification and you can see the need for stability goes up exponentially.
Binoculars Create Eccentric Loads on a Tripod


Mounting Giant Binoculars on a Budget
There are a lot of different suggestions in this thread. They are not all low budget. But there is a wide variety of suggestions made by all the various users, how they view their performance, and a lot of links to various types of products. very good information here.


Binocular Mirror Mount


Neck Monopod Review


I'm looking for a tripod for my binocular. Which tripod is good for holding a binocular up to 25x100?
This question comes up once or twice a month. here's some advice. And links to more advice.
Tripods?



A 7.5# 20x80 mounted on a Bogen 3011 tripod / 3130 fluid head.
Is this a good combination?


Binocular Mounts and Tripods - Farvorite Combos
Several users post what they like to use best as favorite binocular mount combinations


Excellent summary of differences between using photo tripods, parellograms, binocular mirror mounts and binocular chairs. Also, excellent summary of various models of Bogen legs and heads , how tall they are, their weight capacities and some links on where to get good prices.
In addition, references to other tripods and links to articles.
Binocular Tripods


Bogen Manfrotto Models for Heavier Binoculars This discussion took place around selection of a tall tripod to hold 16# load. The recommendations are for big heavy duty Bogen models.


Very good comparison of two models of Bogen tripods. Lots of pictures
Bogen 3051, 3046 side by side


Manfrotto-Bogen Cross Reference




Here's information about the use of the new Universal Astronomics Microstar
Microstar Bino Mount


Here's some info on the popular Orion Paragon Tripods
Orion Paragon or ??

Orion Paragon Tripods

How to Make a Paragon Binocular Mount Adapter This post describes a way to construct your own mount adapter for the Orion Paragon Plus binocular mount. The techniques shown here may have application beyond this specific situation with some adaptations.



This particular post is located in the Mounts Forum but it includes about 10 links to discussions on
Bogen/Manfrotto tripods, Orion Paragon tripods, UA Microstar Mount and a few others.
Manfrotto 3130/3011N for PST, ST80? Other Bogen?




A variety of tripods are listed here with user experiences. It's a good thread to compare one to the other. Must be 10 tripods list in here, everything from department store camera tripods to a link for a full length article on what to look for in a parallogram. Users note some instances where a camera tripod might be all that's needed and some of the pitfalls of using camera tripods for heavy binocular mounts.
Need a sturdy tripod, what do you recommend?


Why don't we see Equatoral Binocular mounts?
Very few positions would ever afford you a level eye position. You would almost always have your head tilted to one side.
mounts and binos


converting a surveyor's tripod to take a mount for a binocular
tripod help


tripods, parallel mounts, and a skywindow for binocular astronomy, some subje...

experience in search of the best tripod/fluid combo for astro binos


What do some other people use as their binocular mount setup? Putting together a versitle parallelogram setup.
Help with a new binocular setup


Home made binocular chairs and parallelogram mounts. Lots of pics.
Observing chair/mount for binos or scopes


One member comments "...I think the 3046 is the best "non-hiking-capable", "budget" astronomy tripod in the Bogen line at around $200. The 3265 head serves its purpose, but I'm now sure that a parallelogram mount is in my future"
Tripod & head report


after a month and a half search, this member chose the Slik 700DX Pro. There were atleast a half dozen other choices offered up as suggestions. Here's the results. Read the rest of the thread for all the other suggestions.
Report: Slik 700DX Pro Tripod



Comments on Binocular to Tripod Adapters

IMHO, the two best tripod adapters are Orion's deluxe (search in Orion accessories), the simple tall L bracket and Universal Astronomic's deluxe. UA's is by far the best. Orion's is thicker metal and taller than most simple L brackets. UA's deluxe is even thicker than Orion's deluxe and it allows the binocs freedom of movement to tilt a little left right. Orion's sell for about 18.95. Ua's sells for $29.95, but it's worth it..

20x80 binoculars are too big for a small L adapter. I'd advise picking up a tall heavy duty binocular L adapter, not just a short thin one. That will help eliminate shakes.

Most large 20x90, 22x100 and 25x100 binoculars do not require a separate adapter. The center mounting post is the adapter.

edz

Orion adaptor

Pentax adapter

Window adapters and tripod adapters

Celestron's adapters, one's metal, one's plastic

comments on plastic adapters

an assortment of adapters, metal, composite and plastic

Nikon 12x50 SE Tripod Adapter


...high quality binoculars in that aperture/magnification range (i.e., the Doctor 15x60 Nobilems, the Zeiss 15x60 B/GATs and the Nikon 18x70 Astroluxes) all use non-standard tripod adapters. The one that Nikon sells for their Prostar and Astrolux binoculars also works for the Zeiss 15x60s and costs less than half as much as Zeiss's tripod adapter. The Doctor Nobilems use a metal tripod adapter that is unique to their binoculars.

Minireview of the Adorama adapter not the favored choice here.

What? No tripod adapter screw hole? Try a strap mount.
Eagle Optics Plate with Velcro Strap mount.

Tripod mounting an old bino with no socket

Narrow body L adapter for mounting Oberwerk Ultra / Garret Signature
standard wide brackets will not work with thiss model binocular. Of course they both come supplied with this bracket, but it's a good one.

a website offering 20 different kinds of adapters
not necessarily all the cheapest offers, but just look at the variety!

FarSight Binocular Mounting Bracket


A not on using a laser pointer on a mount
Here is the paragraph from the FDA's guidelines on laser pointers:

"Laser products promoted for pointing and demonstration purposes are limited to hazard Class IIIa by FDA regulation.

21 CFR 1040.11(b) and 1040.11(c), limit surveying, leveling, and alignment, and demonstration laser products to Class IIIa. This means that pointers are limited to 5 milliwatts output power in the visible wavelength range from 400 to 710 nanometers. There are also limits for any invisible wavelengths and for short pulses. Pointers may not exceed the accessible emission limits of CDRH Class IIIa or IEC1 Class 3R."

Lasers of greater power than 5mW are designated as being Class IIIb lasers and, therefore, are not legal for use as pointers.

How do you mount your BIG binoculars This is a collection of posts showing and discussing various mounts.

Edited by knuklhdastnmr (09/14/13 10:24 AM)


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How to Focus Binoculars new [Re: EdZ]
      #51290 - 02/07/04 10:18 AM

It can be surprising how many people new to using binoculars, or even some who have had them for a long time, do not know the correct procedure to focus binoculars. At every session I teach, there are always a group of people that do not know how. Erik D recently posted this procedure and it was a big help. I'll repeat the post here, but first; A few other things users should know about focusing:

Of course, this relates to binoculars with a Center Focus wheel that moves both eyepieces and a Right Diopter adjustment that moves just the right eyepiece.

If you have binoculars with individual eyepiece focus, just use each separately as if each were a diopter adjustment. Actually, that's exactly what it is.

Best focusing can be achieved by focusing "IN". So start with the eyepiece turned out and "FOCUS IN". Stop when you hit a pinpoint image. Rocking back and forth over the best focus point is not recommended. We have decades of military testing to thank for that little tidbit.

And now from Erik D.

1. Cover the right objective.

2. Look thru the binos while keeping both eyes open and RELAXED.

3. Use the center focus wheel ONLY to achieve sharpest focus. Do NOT try to compensate for out of focus image with your eyes. Let the focus wheel do all the work. Best focus is achieved when star image is the smallest pin-point. This is the same process as if you are looking thru a single EP of a scope. It should be pretty easy to tell if you have achieved best focus because you'll see spikes and flaring of star image otherwise.

4. After you have achieved best focus with you left eye uncover the right objective and cover the LEFT objective.

5. Using the Right Diopter Adjustment (RDA) on the right EP ONLY, focus the image thru the right barrel. Remember to keep both eyes OPEN and RELAXED. Only the RDA should be doing the focusing, not your eyes. Do NOT touch the center focus wheel while your are doing the RDA.

6. When you have achieved pin point focus in your right eye you can remove the cap on the left objective and images in both eyes should be in focus.

The goal of this procedure is to use the RDA to compensate for any difference in eye strength between the left and right eye. You do not have to match them or make them "equal" (by setting them both on the same number).

Make sure your binos are on a solid mount/rest before you attempt this procedure. No one can hand hold 8.8 lb binos and perform critical RDA at the same time.

Erik D

Thanks Erik.




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ABERRATIONS AND DEFICIENCIES new [Re: EdZ]
      #64093 - 03/02/04 06:49 AM

Nikon provides a brief explanation of the six major aberrations here
Nikon Sports Optics - Aberrations and Deficiencies

Vladimir Sacek provides a much more in depth discussion of the major aberrations in his web article here
AMATEUR TELESCOPE OPTICS See INTRINSIC TELESCOPE ABERRATIONS

Tom Trusock wrote a paper with some easy to undersatnd explanations
Telescope Optic Aberrations


MAJOR ABERRATIONS

ASTIGMATISM
Astigmatism makes it difficult to ever achieve a precise focus. The telltale sign of astigmatism is found when you view the out of focus Airy disk image. On one side of focus it will be elongated in one direction. On the other side of focus the elongated orientation of the image will change by 90°. There can be several causes of astigmatism. One of those causes can be a miscollimated or misaligned optical tube. It can be in the eyepieces. It can be in the objective lens. If the optical axis is perfectly aligned and the if the images are merged between the two barrels and astigmatism is still present, the problem is not one the user can fix. At any rate, the affect of astigmatism is that you will notice elongated images off axis. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint. The affects of astigmatism are generally eliminated with high power and small exit pupil, but that is usually not achieved in binoculars.


SPHERICAL ABERRATION
Spherical aberration is a displacement of the rays along the length of the optical axis. Rays originating in the lens further off axis do not reach the same focus point as on-axis rays. If present, even on-axis images may look considerably soft and no amount of refocusing or flattener will help to improve. The best you can achieve is focusing on what is known as a least circle of confusion.

Stopping down or masking the outer edges of an objective will help suppress spherical aberration. This would have the effect of eliminating improper focal length rays generated at the extreme outer portion of the lens. This would improve or "reduce in size" the least circle of confusion at or near the focal plane. This would give a more pinpoint image to focused stars, but, at the expense of lost aperture.


DISTORTION and FIELD CURVATURE
Q - I was hoping someone could explain to me the difference between distortion and field curvature? At the very edge of fov in my binocs I am noticing the stars stretched out a hair compared to very tight dots in the center to about 90% out.

A - By Bill Tschumy
Distortion is of two types: barrel distortion and pincushion distortion. It isn't related to sharpness of the image, but rather image scale across the FOV. If you look at a square centered in the FOV, with pincushion distortion, the sides of the square will be bowed inwards. With barrel distortion, the sides will bow out. Generally, when looking at a star field, the distortion is not much of an issue. Sometimes, when panning, barrel distortion can give a "rolling" effect that makes some people dizzy.

Field curvature is when the outside of the field of view has a different focal point than the center. You can't get both in focus at the same time but you can get one or the other in focus.

What you describe as the stars being stretched out near the field sound more like coma to me, yet another aberration.


Bill T dedcribed distortion and curvature pretty well. As Bill said, "It (distortion) isn't related to sharpness of the image". Distortion does not affect the image of the star, it simply moves it in the field of view. Generally it cannot even be seen in astronomy, but can usually be seen when the binocular is used for looking at terrestrial objects where we are accustomed to seeing nice straight line edges of things like buildings and poles.

Pin Cushion Distortion discussion explaining reasons for pincushion

PINCUSHION DISTORTION IN BINOCULARS drawings showing pincushion


FIELD FLATTENERS TO REDUCE CURVATURE
Curvature of field (change in focus off-axis)can be reduced by using a field flattener lens. Without the flattener, the outer portions of the field will be slightly out of focus when the center is in focus. Instead of pinpoints in the outer field, this will have the tendency to enlarge and blur the circles of light that form the stars in the outer field. They would be slightly out of focus. (Slightly enlarged circles, that is assuming no other aberrations are present).

A field flattener can be used to insure that the entire field is in focus at the same time. Stars in the outer field will be focused and appear just as stars in the center (again, assuming no other aberrations are present). The field flattener does not eliminate spherical aberration, astigmatism, coma or chromatic aberration.
Field Flattener vs Field Aberrations


Field Curvature Affect on Depth of Field
Of the aberrations mentioned above only one can be changed by refocusing, field curvature. Field curvature appears because the outer portion of the field of view may have a different focal point than the center. The focal length increases as you move further out in the fov. You can't get both the center and the edge of the fov in focus at the same time but you can get one or the other in focus.

An astronomer would prefer all binoculars to have as little field curvature as possible so the entire plane of the fov has as little distortion as possible. It is not unusual to find that a binocular with much less sharpness out at 60 or 70% in the fov has a much greater amount of field curvature than a binocular which appears sharp out to 80-90% of the fov.

A terrestrial viewer might want to consider how field curvature affects the view, and may in fact find field curvature to be a useful aberration. While it does nothing to add to depth of field further distant than the plane of focus, field curvature provides for closer objects to appear in focus as they range out across the fov.

It seems clear from this correlation that the binoculars with greater field curvature have the perception of greater depth of field in front of the focus point. Therefore, it may stand to reason, a binocular with more field curvature may provide a greater “near” depth of field for the terra user. (of course that won't do you any good if all the birds you want to see are in the same tree sitting on branches between 45m-55m away). Also, it may be that a field flattener lens, which would be desirable for an astro viewer to get as flat a field as possible, might work against a terrestrial viewer looking for the greatest depth of field.

Curvature Affect on Apparent Depth on Field



COMA
Coma is generated by off-axis light rays. The intersection of light rays from different points along the objective is not symetrical. Coma is present when you see images of stars begin to spread out in a fan shape. Rather than see a tight spot of all the rays forming the image, a diagram would show most of the rays forming the bright point and the remainder of the rays spreading out from that point to form the recognizable fan or comet shape. Coma increases toward the outer edges of the lens. A star will have its brightest point towards the center with the fan shape extending outward.


CHROMATIC ABERRATION
this topic has been moved to its own thread

All achromats show some CA. It is a function of lens design. It is also a function of focal ratio. Very few binoculars are designed specifically to suppress CA. BTW, CA is not considered a major aberration. Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point. Lateral CA increases as you view objects further off axis and is more pronounced towards the outer edge of the lens. Lateral CA is seen as the outer edge of the object bleeding, usually a different color, generally observed in large bright extended objects. Significant CA (on the moon or planets) may cause some edge softness on both and loss of contrast, but it should not be confused with flaring.


Quote:

Many of the aberrations we see in binoculars affect edge performance. In fact, the aberrations described here all look somewhat different and affect different areas of the view.

WHAT DO ABERRATIONS LOOK LIKE

ON_AXIS
Generally, not all aberrations are seen on-axis. The on-axis image created by aberrations is as follows:

curvature not seen on-axis.

coma not seen on-axis.

If the stars seem never to focus to a fine point, but at best remain slightly bloated and are still circular, and it cannot be focused out it is probably spherical aberration.

If the star seems to not come into sharp focus it may be astigmatism. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint. Passing in and out of focus will show the out-of-focus image to flip orientation by 90°.

Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point. Sometimes seen as a small circular band of color areond a finely focused star point.

OFF_AXIS
As for how you notice stars in the outer fov, the image created by aberrations is as follows:

If the star seems slightly bloated, but it can be refocused down to a finer point, then it is curvature, as Bill T described.

If the stars seem flared as wedges with the point towards the middle and the flared wedge toward the outer edge, them it is coma. It cannot be focused out.

If the stars seem slightly bloated but are still circular, and it cannot be focused out it is spherical aberration.

If the star seems slightly bloated and slightly elongated than it is astigmatism. Astigmatism will show elongated images off axis. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint.

If you have both astigmatism and coma, the off axis images will look like comets with an oblong axis, or like seagulls.

Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point.

Lateral CA will produce color fringes around all bright objects when viewed slightly off axis, but you should see a different color towards the lens center than you see towards the lens edge.







Spherical Aberration usually is referred to as an aberration in the optical elements. However, when referred to in the exit pupil, usually what is meant is "Kidney Bean". Read the explanations here.
Spherical Aberration of the Exit Pupil


Binocular deficiencies to watch out for:

GHOST IMAGES
Coated vs Multi-coated vs Fully MC will have an affect on total light transmission and contrast. Lack of coatings may produce ghost images internally. Ghost Images and internal reflections is a deficiency that will destroy contrast.

PRISM LIGHT CUTOFF
The following post has a photo of a binocular through the objective lens. look closely at the image and you can see light blockage at the edges. This is known as prism light cutoff. The net effect = this is reducing the effective apperture of your binocular.

Here's the photo of prism light cutoff
Prism Light Cutoff shown in photo

In this image above here you see the perfect example of prism light cutoff.

This is not related to collimating binoculars. This is not what you would see if one side or both sides of the binocular were out of collimation within the tubes themselves. In that case you might see ovals or cats eyes or the images would not be merged.

In this picture, either the prism housing infringes in the path or prisms themselves are so large that they infringe in the light path, or the prisms are to small to accept the entire light path from the objective and you see the edges of the prism cutting into the light path and cutting off the edges of the exit pupil.

Here's a link to the discussion and the description of what is going on in this binocular system
Prism Light Cutoff ...

Here's a link to another discussion as relates to another model binocular
Prism Light Cutoff - What to look for - How to calculate


COLLIMATION
A binocular that is out of collimation will show double images. It is corrected by mechanical adjustment.
This has been moved to it's own post.


FLARING
Q - I see flaring of the stars in my binocular? What is it?

A - I'm not sure what you mean by flaring. In fact I think people have different meanings for this term. I think some people are referring to radial spiking and some to ghosting. Flaring in photographic images refers to something similar to ghosting, as in lens flare. There are other things people might mean when they say flaring.

What some people are calling flaring might be lateral chromatic aberrtion. Lateral CA increases the further off-axis you view the object and is more pronounced towards the outer edge of the lens. Lateral CA is seen as the outer edge of the object bleeding, usually a different color than the inner edge, generally observed on very bright stars or large bright extended objects and would have a smooth outer edge shaped to the object.

Coma is another good example of an aberration that people might refer to as flaring. Coma would be seen as a off-axis wedge with the point of the wedge towards the center. Generally not noticed on-axis, the wedge would probably get larger as you move the object further off axis. Coma would be seen on all stars.

Severe spherical aberration could be producing an on-axis image that looks like a star point encircled by a diffuse circle of light. The inability to focus all the light into a fine point creates a diffuse glow around the point that cannot be focused out, either on or off axis. This might be interpreted as flare by some people.


However I use the term flaring to mean radial spikes, spikes of light flaring off of the central image disk, more than just a few, and in all directions. The binocular that I had with this problem displayed maybe 30-40 flares coming off the star.
In this thread About two years ago I described flaring as radial spikes.
More recently, the discussion came up again and much discussion was devoted to problems in the eyes in this thread about
Radial Spikes Around Bright Stars


RADIAL SPIKING
On bright stars, I'm seeing a rather nice radial pattern of spikes around the point star. The pattern doesn't flare or move like atmospheric abberations, it remains static as long as I hold my eye still. As I move my eye around the spikes move around as well, but never disappear.
When using both eyes, I cannot get stars to focus to points no matter how I set the diopter and focuser. I have 20-20 vision BTW.

New 20x80 binos - Radial Spikes

The problem Gary describes has nothing to do with mis-collimation nor mis-alignment of any portion of the optical train. Gary describes radial spikes, something akin to radial flaring. This is an anomoly of the lens.

This abberation is similar to some degree to what you might see in a normal lens on a very bright star. Focus on Sirius or Vega and what do you see. In many binocular lenses, there will be what looks like a few, maybe 6 to 8, small diffraction spikes eminating from the bright star. This is usually seen ONLY on the most extreme bright objects.

What Gary has described is radial spikes all around a star. I have seen this aberation exactly as described. This is an unusual abberation that is not normally seen in a lens.

A star test, if viewed on a group of faint 4th /5th magnitude stars would not pick up this abberation. By the time the view moves over to 5th or 6th magnitude stars, there is not enough light for this anomoly to be seen, but it is still there. It will interfere with resolution of bright close objects, especially if the companion is faint, and it will interfere with resolution of extended objects made up of point sources such as very dense open clusters and all globular clusters.

If this is indeed a lens condition, the only kind of test that would detect it is a severe star test, similar to that used to test the diffraction pattern in a telescope. This is not a condition that would normally be discovered by any QC.

I have tested a number of binoculars and looked closely for any appearance in the diffraction image in all of them. At powers of 15x or below, separation in the diffraction rings cannot even be seen. At 16x it can barely be noticed. At 20x the first real definition of the diffraction rings begins to appear.

I would suspect flaring is a result of the figuring of the lenses use in the manufacture. It could be in the objective lenses or the eyepiece lenses. Figuring of the lenses could also be producing soft focus and not appear as flaring.

After much discussion and searching by many people, it seems several tend to agree that a strong contender as a source may be that this problem is caused by pinched optics. It may be a result of uneven pressure during the cementing of a doublet or it may be the retaining ring around the objectice being too tight. Read page 150 of Suiter.

It is also a simple fact that very bright objects produce some flare or minor spikes in the image. Here again, I would expect a more highly figured lens would reduce this flare.



VIGNETTE
Vignette, or the blocking of light, by whatever means, reduces the amount of light delivered by the optical system before it eventually reaches the receptor which in this case is your eyes. There are several different deficiencies that could be causing vignette. Identifying what is causing it is more difficult than identifying how much of a light loss is present. This is a very lengthy thread. I have singled out very specific passages for the reader. Fell free to read the entire 100+ posts if you wish.

methodology of the assessment of vignetting by visual inspection
Glenn LeDrew on Vignetting

Vignette in Binoculars!! YES it's there

Test procedure using a laser light to check Vignette in binoculars

Vignetting in All Binoculars!! the prism is not fully lit by the entire objective

Why can't we see the light drop off?

Graphic representation by field of view

Graphic Representations by % light in exit pupil (see attachment)

Graphic Representation showing affect of Off-Center Exit Pupil on the Overall Light Distribution in the Exit Pupil


EdZ's 22 x 85 GO Signatures
Tests and explanations of vignette that reduces full aperture to some effective aperture.
Pictoral essay showing vignette in beam transfer thru prisms, explaining how to conduct the target laser tests. Shows Illumination and Optical Tilt.
This is the exact same test as was first outlined in the "Vignette" threads above back in April 2004. the testing procedure is identical. The presentation is different. the outcome is the same. Actually I explained how to conduct this same test back on '04, but few people understood it.

Aslo page down thru this thread
Comparing GO22x85, WO22x70, Tak22x60
and you will see photos of several binoculars showing the vignette when lining up the edge of the prism with the edge of the objective. This also mimics the results that you get from the laser vignette testing procedure outlined above.

We often hear people state, exit pupil is what determines the brightness of your binoculars. But stop for a moment and think, that does not explain why sometimes it seems that two binoculars even with the same size exit pupil, do not appear to be equally bright. The above tests that show the extent of the Illumination of the Exit Pupil do explain why one model can be brighter than another. It is not just exit pupil which determines brightness of image. It is also dependant on the maximum extent of full illumination. Internal vignette is the cause of reduced illumination. The thead Comparison of 22x binoculars gives good support to this statement.


Things you should know about "too small" prisms

Comments on use of stops

More on stops


Edited by EdZ (05/02/11 02:27 PM)


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Binocular Articles over on the Reviews side of CN new [Re: EdZ]
      #65290 - 03/03/04 10:55 PM

This particluar post is a bit out of form with all the others here that link to info in the binocular forum. This one links to a binocular articles and reports over on the CN reports / reviews / articles side of Cloudy Nights. These are worthwhile to those searching for information related to binoculars.

How To Measure TFOV Of Binoculars


Bear 15x70 Binocular Minor Collimation Procedures


“Collimating” Binoculars
How to perform conditional alignment with prism screw adjustments


My Comet Couch! How to make your own binocular chair/mount


Globular Clusters For Binoculars

100 Binocular Deep Sky Objects

CN Reviews INDEX to Binocular Reviews

Binocular Observing Report using Four Models

Free Mag 7 Star Charts

Books for Astronomy: For use by novice and avid intermediate astronomy enthusiasts

Binocular Mounts, Tripods & Mounting

More selections of Binocular Mounts including Mirror Mounts

Zeiss Premoistened Lens Cloths


Binocular Astronomy by Crossen and Tirion


Technical Lab Report - Limiting Magnitude in Binoculars

Technical Lab Report - How to Understand Binocular Performance

Technical Lab Report - Affect of Eye Pupil on Binocular Aperture


A Comprehensive review of a 7x35, 10x50, 15x70 and 16x80
includes Minolta Standard 7x35, Orion Ultraview 10x50, Oberwerk 15x70 2002 model, Orion Giant 16x80

A Comprehensive Comparison of Four Binoculars 12x50, 15x70, 16x70 and 20x80
includes Pentax PCF III 12x50, Oberwerk 15x70 2003 FMC model, Fujinon FMT-SX 16x70, Oberwerk Deluxe (original) 20x80 . also includes brief info on Minolta Activa 7x35, Orion Vista 8x42, Nikon Sky & Earth Kestrel 10x50, Orion Ultraview 10x50, Minolta Standard XL 12x50, and Orion Giant 16x80

CN Technical Reports - Giant Binocular Review 100mm Binocular - What Can You See?
Primary comparison is the Celestron Skymaster 25x100 and Oberwerk Giant 22x100 . Also included are Oberwerk BT100 and Oberwerk Standard 20x80.
Brief info on Fujinon FMT-SX 16x70, Oberwerk 15x70 and Nikon SE 12x50.


CN Technical Reports - Small Binocular Review 8x, 10x, 12x Binoculars
Comprehensive review of Nikon Action Extremes 8x40, 10x50 and 12x50
Also includes Swift Ultralite 8x42, Orion Ultraview 10x50, Pentax PCF WP 10x50, Pentax PCF III 12x50, Nikon SE 12x50.


CN Technical Reports - 100MM Binocular Tests and Comparisons
Comprehensive Review of Oberwerk 25x100, Celestron 25x100 Skymaster, Garrett Optical 20x80 Gemini, Oberwerk BT100 Binocular Telescope . Brief Info included on Oberwerk 15x70, Fujinon 16x70, Oberwerk 20x80 Standard

Garrett Optical 25x100 IF Binoculars
If you decide to acquire these make sure you’ve got a mount that will easily handle the ten pounds, do take the time to balance them correctly, and seriously consider adding an index finder. So configured and equipped, they will provide outstanding and memorable tours of the night sky.

Miyauchi Saturn III vs Tele Vue 127
comparison of a high quality 5" APO (TeleVue NP-127) with DenkII binoviewers Vs. the Saturn III. Of course the APO/Denk combination is more than three times the cost of the Saturn III - but just how do they measure up for two-eye viewing at a comparable power? The Saturn III is a long FL binocular (39x100 at F7.5) that has the distinct merits of being very light (only 13 lbs) and offering 45-degree viewing.

CN Report: Oberwerk Ultra 15x70
There are a number of importers/distributors currently offering what appears to be the same binocular. Keep in mind, none of these importers/distributors actually make these binoculars. Oberwerk, Garrett, APM, AP, General Hi-T, TS, AOE, they all import these binoculars, variously referred to as Ultra, Grizzley, Marine, Premium, etc. Thsi comprehensive review discusses all aspects of optical and mechanical quality and compares these binoculars to several other well know 70mm and 80mm binoculars.




Edited by EdZ (01/26/07 04:46 PM)


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If They Look the Same, What Could be Different? new [Re: EdZ]
      #71821 - 03/15/04 07:06 AM

We see this question all the time. "They look exactly the same on the outside. Why would anyone pay more if you can get the same thing for less"? Usually, it's because they are much different on the inside.

One of the things we've been trying to teach people for years is there are a list of some of the differences you CAN'T see. Some are highlighted here:

Contrary to what you might read elsewhere, any shortcuts that can be allowed in the manufacturing process will result in a less expensive product that can be distrubuted for lower cost. Considerable savings in time and process results in a less expensive product, a much bigger savings than a few $$, but one that will not perform as well.

Probably the most important differences in any two binoculars that look the same but sell for much different prices is (A)the mechanical construction, workings and range of adjustment, and (B)(likely more important) the degree to which all the optical surfaces have been figured, polished and coated. There are other things that make a difference in the quality and most of them are not visible on the outside.

If one dealer orders all his binoculars without coated prisms, the manufacturer can simply take the prisms off the shelf and install them directly without putting the prisms through the 3 hour process of the coating machine and then inspection.

It is not the cost of the automated polishing machine that adds to your cost, it is the cost of an individual testing and inspecting each piece of glass before it passes the level of QC demanded by the distributor.

Uncoated or single coated lenses or prisms will considerably increase the amount of light that gets reflected around the inside of the binocular, causing ghost images and reducing image contrast. A fully multi coated binocular requires multi-coating on ALL surfaces. It was discovered several years ago that that the factory claim of fully multicoated was being applied to binoculars that had some multi-coated components and some single coated components. This type of factory claim is still passed on by some importers.

You could be getting lenses that have passed a specific selection criteria for the objectives in one binocular. For another brand binocular, you could get lenses that have not passed the test for brand A, so you take your chances. For a third brand, you may be getting the lenses that did not pass any inspection criteria used to get the lenses in the first two brands noted above. You don't honestly think they throw away all the lenses that do not meet a specified test criteria, do you? Just because they don't meet the criteria for brand A or B doesn't mean they can't be used for brand C. More on this below.

The same binocular body could be fitted out with very different eyepieces and still look exactly the same. I once tested 3 different 20mm plossl eyepieces. They ranged in price from $29 to $89. With minor modifications they could all be fit into the same eyepiece housing. The difference in performance between the three was like night and day. The lowest cost 20mm eyepiece had severe distortion in the outer 40-50% of the field of view and beyond 60% out from center lost a full magnitude to the best eyepiece. The best 20mm eyepiece could still see not only the faintest stars but also very fine resolution at the extreme edge of the field stop.

Sometimes we have binoculars that appear exactly the same, but one model has a much wider field of view than the other. This can be accomplished by simply eliminating the field stop from the eyepiece housing. Of course, what you end up with is a wider fov, but it is not a sharply defined field stop and is generally mush towards the outer edges. Also, this may allow undesirable stray light to enter the fov. Neither the removal of the field stop for the wider soft field nor the stray light improves the image, but it is cheaper to make the eyepieces without the field stop.

The eyepiece lens edges could be blackened or not.
The objective lens edges could be blackened or not.

Shiny or bright metal exposed surfaces on inside of barrels will diminish contrast. Not all binoculars are fully blackened at all internal surfaces.

If a lens has several layers of MgF, then it is multicoated. If so, it may likely not have the characteristic blue color of a single MgF coated lens. A properly multicoated lens surface may reflect only 0.2% to 0.5% of the entering light. A properly single-coated lens surface may reflect only 1.5% of the light. An uncoated lens surface may reflect 4% of the light. Considering a binocular might have 12 to 18 surfaces, the importance of multicoating soon becomes evident.

Probably just as important is simply having multicaotings is the precise control of the thickness of the coating process. An improperly controlled multi-coating process can produce a lens coating that reflects more light than a single coating. Although you can't truely determine anything about the precision of the coating application by the color of the coating, in general, poorly coated lenses tend to look bright green. The bright green color could result from coatings being applied too thick. Improper coating thickness will reflect more light than it should, reduce the light transmission of the optics and if bad enough may cause internal reflections.

Lenses that fail the extremely tight tollerances required in the coating process should not be categorized as premium multicoated lenses. But they are still multi-coated lenses and will be used in the manufacture of some brand of binocular (same as objectives mentioned above that don't pass QC criteria). So you could be buying a fully multi-coated binocular that has lenses that don't meet stringent coating thickness criteria.

Here is a quote from a highly respected individual that has been associated with the optics industry. His comments below pertain also to my comments above re: QC of lenses and coatings.

Quote:

I've worked in the optical industry a bit, so I have a fair idea what the limiting factor in the quality of binoculars made for the mass market is.

Prisms aren't particularly easy to fabricate to really high levels of quality. The "quality sieve" method may help keep costs down, but they're still not cheap to make. (The "quality sieve" method of production was described to me by a fellow who had worked with the Japanese exporter of fine optics many years ago. A fabricator would make, say 1000 prisms, lens sets, whatever. Only the ones which met the higherst standards would be shipped to the most discriminating customer, say the best 200. The next 200 would be shipped to a customer who had high standards, but not so high as the "top dog", and so on, until the glass is all gone. The prisms that make it into the "no-name" binocs you buy at K-Mart for $19.95 likely came from the "bottom 200"!)

Rick Shaffer




So there you have it. They may look exactly the same on the outside, but Oh, there are so many possiblities for differences.

edz


These Look The Same, are they?
This post summarizes a lot of the quality differences that might exist be between various brands and price levels of binoculars, most of which would never be evident by looking at the outside of the binocular. With this post we try to do our best to provide you the information you need to dispense with the often heard internet myth that they are all the same. It's just not so.




Is it worth it to pay more to get more? Are you actually getting more? What are the problems with lesser priced products?


Things to watch out for in cheap binoculars

There are many other posts that discuss much more. I will link to them as I find them

Are these the same?



http://www.binocularschina.com/binoculars/giant_binoculars.html

http://www.united-optics.com/index.html


and last, but not least, this particular thread is an approach to this subject from a completely different angle
10 Reasons to Spend $1000 on "Little" Binos

edz

Edited by Zdee (06/27/12 08:06 PM)


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Cleaning Lenses - Binoc Repair Eyeguards - Caps new [Re: EdZ]
      #71869 - 03/15/04 09:36 AM

This is another question that keeps coming up all the time.

Here's some info. Note it varies by individual. Which method is best? The one that takes the most care with the least frequency. Cleaning binoculars is the same as eyepieces and scope lenses. they are all coated optics.

Caution should be exercised by any individual who happens upon this thread looking for information intending to clean a dielectric coated surface. Dielectric coatings include TV everbright diagonals and similar products

for binoculars and other normally coated lenses this offsite website provides excellent advice
Arkansas Sky Observatory - Fine Optics CLEANING SYSTEM

This is how an experienced optical repairman cleans
Cleaning Binoculars

Read this thread for cleaning methods by some of our users
More comments on cleaning

read what Orion says about how to clean binoculars
Orion website instructions for cleaning the Ultraviews

here's a link to an article over on the CN reviews side
Cleaning Eyepieces

here's what NOT to do
I ruined an eyepiece

Steps to take to help avoid cleaning
A quick, successful dust removal!

If you want to take the time to wade through this thread, there are plenty more opinions
cleaning EPs



Need Serious Internal Cleaning??
See this thread for links to repair services

Repair Services
links to binocular repair and/or collimation services
Binos need Cleaning or Repair or Adjustment about a dozen different links


Replacing Rubber Eyeguards and binoculars objective lens caps

Eyepiece caps and Lens caps
Binoculars and Eyepiece Lens Caps




Edited by csa/montana (10/08/09 09:44 AM)


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Need Binocular COLLIMATING or Repair? new [Re: EdZ]
      #73181 - 03/17/04 12:08 PM

For most binoculars with a minor need for an alignment adjustment, turning the prism tilt screws is the primary means available to the end user and is an appropriate adjustment, called conditional alignment, but commonly referred to as collimation. True collimation can only be accomplished by a qualified repair service with the proper instruments.

Repair Services
links to binocular repair and/or collimation services
Binos need Cleaning or Repair or Adjustment about a dozen different links
Suggestions Please / Repairs
Binocular Repair


COLLIMATION
Collimating binoculars takes on two different meanings. The first and most common that everybody knows is to get the images from one barrel to merge with the other. But the second and much more difficult problem is the alignment of the optical elements along the optical axis in each tube separately. The first is really conditional alignment while the second is true collimation.

See this article in CN reviews dealing with conditional alignment
“Collimating” Binoculars

And see this article here in the forum dealing with collimation
Binocular Collimation and conditional alignment by Bill Cook
2) Alignment that is within the original JTII standards can be considered to function as “perfect” in that the eyes can easily accommodate the error without introducing noticeable eyestrain. For example, an 8 power instrument should have errors equal to or less than 4’ Step, 10’ Divergence and 6’ convergence, with a 16 power having 2’, 6’ and 3’ respectively.

or
JTII @ 4.5 power
8 ' and under for step (dipvergence)
20 ' and under for divergence
15 ' and under for convergence

Cheers,
Bill


and see this for some ALLOWABLE TOLLERANCES
Test for Convergence or Divergence

also see this
A lengthy discussion of collimation tollerances
as posted on different websites and by different manufacturers.
You'd never know by the thread topic that this is 90% of the content in this thread.


MERGING THE IMAGES
I'd recommend you assess the degree of miscollimation before attempting any adjustments.

Do you normally wear glasses? Do you have astigmatism? If no, OK, proceed. If you do have astigmatism, do not attempt to even visually test for miscollimation without your glasses.

Are you familiar with some double stars, test collimation on a double star of known separation. This gives you a benchmark separation from which you can determine the severity of miscollimation.

There are allowable tollerances. Standards seem to be more than I personally can tollerate, but you could easily have 2 to 3 arcmin of miscollimation and need no adjustment at all. Standards would indicate greater deviation is allowable. The tollerances get much tighter as magnification increases. A 7x or 8x binocular with 2 to 3 arcmin miscollimation won't look bad at all. However, in a 25x binocular with even 50 to 60 arcseconds of miscollimation it may be difficult to merge images.

An excellent double to test collimation is Nu (v) Draco. It has a separation of 62". It's like having a 1 arcmin measuring device in your image. If your low power binocular collimation is within 2 or 3 times the separation of Nu Draco, you may want to just leave it alone.

Miscollimation would produce a well lit exit pupil with black edges all around. It may or may not be round, ...but it should have dark all the way around it.

If it is determined as necessary to adjust the binocs, the amount of turn on these screws is very very small. You might turn each screw less than a quarter of a turn to reach adjustment.

Keep in mind that adjusting the screws to merge the images is being done without the use of any lab equipment. The eyes can tell when images are not merged, but they cannot tell which of the four prisms are the ones causing the misalignment.

The general trend is to stick with adjusting the two screws closest to the eyepiece end of the tube. However you have no way of knowing that they are the proper screws to adjust.

Sometimes you see or hear discussion of problems related to binoculars that seem to be in alignment (merged), but the exit pupils are not round. One possible cause of this condition is adjusting the wrong screws. If the front prism is slightly tilted and is causing misalignment but the back prism is adjusted to reset alignment, what you now have is two prisms that are both set incorrectly. The result may be an image that appears centered and aligned with the opposite barrel, but it would not be surprising to see oval exit pupils, out of round diffraction pattern or field of view not matching the other barrel.

In some cases turning prism screws can make the situation worse

A root cause of this condition is an objective lens that is not seated exactly centered and perpendicular to the optical axis. This may be the underlying condition that is forcing the adjustment of the prism screws to get the images merged.

In a truely collimated and aligned binocular, prism surfaces are perfectly perpendicular to the incoming light path and prism pairs are also perfectly parallel to each other. Tilting prisms to accomodate any deviation of either of these above conditions to result in merged images is done to compensate for some other misalignment in the light path and may result in one of the exit pupil or field of view conditions mentioned above.

For any binocular with a very minor need for adjustment, turning the prism tilt screws is the primary means available to the end user and is an appropriate adjustment. However, True collimation can only be accomplished by a qualified repair service with the proper instruments.

Conditional alignment vs. true collimation

Visual alignment of the field of view can be checked in daylight. However it is not recommended that any sort of prism adjustment be made based on a daylight condition. For adjustment, the light source should produce such a small point of light, it is generally thought that stars are the best source for this visual test.

WHERE TO FIND THE PRISM ADJUSTMENT SCREWS
Back (Eyepiece end) prism screw
Front (Objective end) prism screw


MISALIGNMENT OF THE OPTICAL AXIS
If you adjusted the wrong prism or if you were seeing an out of alignment optical tube, similar to a refractor tube that is not collimated, you might see an oval exit pupil. You would not see an oval shape in the exit pupil from the objective end. It must be viewed in the exit pupil at the eyepiece end. From the objective end, you might see that it would force you to view off center to see the full circle of light rather than viewing down the center of the axis of the light path.

Look here
Cat's Eyes

Oval or cat's eye shape in the exit pupil would be a clear indication that the light path in that side of the binocular is not on the optical axis. Could be several things causing it. All have to do with the alignment of the optical path in that barrel. They all end in the result of reducing the light output, which can be significant.

Here is an excellent pictoral of the view thru one barrel of a binocular with interchangable eyepieces. in place of the eyepiece is a Cheshire eyepiece. You can easily see when the optical alignment is off in one barrel.
Using a Cheshire Eyepiece to check an interchangable eyepiece binocular


Generally there are three collimation errors to be concerned about. For all misalignments the allowable error is smaller as magnification increases. Actually this results in the same apparent visual error, the angular error multiplied by the magnification.

Vertical Alignment, a serious error, is when one image is higher than the other image. The eyes have no muscles to accommodate for vertical error. The allowable divergence is only 4 arcmin at 7x to 10x, only 3 arcmin at 12x to 15x and 2 arcminutes at 15x to 20x. Personally, I cannot tollerate even 2 to 3 arcminutes of vertical error even at magnifications of 10x and only 1 arcmin at 16x.

Horizontal Convergence, the least problematic error, is when the image in the right eyepiece is to the left of the image in the left eyepiece. You might think of this as cross-eyed. The most separation can be tolerated in horizontal convergence, 10 arcmin at 7x to 10x, 8 arcmin at 12x to 15x and 6 arcmin at 15x to 20x. Most eyes can readily accommodate this error, but these limits I find a little too wide. I could not tollerate even half that much.

Horizontal Divergence, another serious error, is when the image in the right eyepiece is to the right of the image in the left eyepiece. The images are spread apart, an error that the eyes cannot accommodate without strain. The allowable error for horizontal divergence is 6 arcmin at 7x to 10x and only 4 arcmin at 12x to 15x and 3 arcmin at 15x to 20x.

Keep in mind, the magnification of your binocular has a significant influence on how you see this error. Your eyes see the apparent error, or the angular error multiplied by the magnification. For instance a 3 arcminute error in a 10x binocular will appear to have a magnified apparent size of 30 arcminutes. That same error in a 15x binocular will have an unacceptable apparent size of 45 arcminutes and in a 20x binocular will appear as 60 arcminutes apparent error.

For reference 1 inch at 100 yards is just slightly less than 1 arcminute.

Personally I cannot accomodate my eyes to these tollerances. I would recommend cutting all of these in half. HD is the error I see almost all the time. Because of the way the prisms rotate, there is always some vertical alignment error with it. I can accomodate 2-3 arcmin error at 10x-12x. I begin to find it difficult to accomodate a 2 arcmin error at 15x-16x. I could not tolerate 2 arcmin error at 20x. In large binoculars at 25x or higher, I find any collimation error of more than 1 arcminute unacceptable. I have my BT100 at 44x merged to about 20 arcsec.

Rotational Error, a fourth collimation error, is when one image is rotated in relation to the other image. I have never seen it in any binocular.

Suspect your binoculars are out of collimation and you want to know by how much? Observe a known double star such as nu Draco (62 arcseconds) and allow your eyes to relax so you can observe the error. Use the spread of the double to compare to the spread of the collimation error.

Collimation error can be measured in an instrument by observing a variety of double stars of varying separations and watching as the stars try to merge. The separation of the double is used as a scale in your view. Compare the miscollimation error to the separation of the double. I test mid-sized 10x-15x binoculars using a 60" double. For 20x-25x, and for binocular telescopes depending on the power at which you use them, you need to test with doubles more like 20" or 15" or 10" or even less. To observe comfortably at powers between 50x-100x, you might need your BT merged to within a tollerance of less than 30 arcseconds.

A few test targets
Stf 485, Cam 7.0-7.1/18”, 4h05m +61n, easy, in o.c. 1502
Stf 2690 Del 7.0-7.2/16.7", 20h35m +11.5n,
100 Herc, 5.9-6.0/14.2"
5 Ari, gamma 4.8-4.8/7.8" PA 000,
11 Mon, beta, 4.7-5.2/7.3”, C=6.1/10”, BC=2.8”, seen as A-BC = 4.7-4.8/7.3”
Stf 232, Tri, 7.9-7.8/6.6”, 2h15m +31n, near 6 Tri,
95 Her, 5.0-5.1/6.3”, 5° ssw of 100Her,
16 Zeta Cnc, AB-C 5.0-6.0/6.0”,

edz



Collimation on a MkV explained by daniel_h who attended a course on binocular collimation taught by Cory Suddarth.

Does anyone know if it is possible to build/buy a binocular collimator for something less than $100?

A comment on collimating binoculars (or how you might screw up the collimation of your binoculars)

Where to find the prism adjustment screws on the Oberwerk Ultra, GO Signature, AP Premium, Resolux, Etc
Photo of Screw Location


Edited by Richard McC (11/24/11 04:28 AM)


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Contrast new [Re: EdZ]
      #75304 - 03/20/04 08:48 PM

In essence, adding magnification decreases exit pupil and reduces brightness, but it does not increase contrast. It only gives the perception of increased contrast on stars because the faint stars in the view becomes easier to see with added magnification. What happens when you add magnification to your existing aperture is the sky background, which is an extended object, gets darkened. But all other extended objects would get equally darker. However, the object has some perceptible light gradient difference (contrast) with the background and its contrast difference with the sky background is maintained, not increased or decreased. As the object gets larger the perception is it has become easier to see. While it may possibly be made easier to see with the optimum magnification, this is improperly interpreted as increased contrast.

Post in the above noted thread that includes links to some of the best written works on contrast.

Thread on CONTRAST with links explaining Optimum Detection Magnification


And posts in this thread that include even more works on ODM and contrast
Exit Pupil Overrated


Please refer to these two written works by Bill Ferris which provide some of the best and easiest to understand explanations of contrast that you are likely to find anywhere.
An Explanation of Contrast Ratio by Bill Ferris

An offsite paper by Bill Ferris explaining contrast threshold
Lowering the Threshold



What other quality aspects affect contrast?
Among other things, contrast is reduced by reflected internal light (which also is a result of poor or no coatings), improper or no baffles which permits stray light to interfer, poorly polished glass surfaces which produce scatter, poorly figured lenses which produce poor resolution and reduce the amount of light in the Airy disk, chromatic aberration which reduces the concentration of all colors of light in the Airy disk and spherical aberration which increases the size of the point image instead of concentrating the light to a point.

Are coatings more important for large exit pupils?
this thread title belies the content of the thread. The discussion revolves around contrast, but rather than just discussing the importance of coatings, it contains discussion of how contrast is not only affected by lesser quality coatings, but also by: sky conditions bright or dark therefore apparent contrast, larger aperture therefore larger exit pupil, smaller aperture therefore lower light gathering, lens aberrations, eye pupils, masking the aperture, lower magnification therefore larger exit pupil, higher magnification therefore smaller exit pupil but also larger image scale.



Users comment on contrast.

Please note, some of these following explanations apply to stars and this is improperly described as contrast. In some cases below this is explained.

Exit pupil is also a factor in contrast. I find that 3-4mm works best for my skies (also good for compensating for my astigmatism), but at 5mm the contrast starts to fade, at 6mm the skies begin to wash out and fainter stars disappear, and at 7mm, the skies look brighter through the bins than naked eye, if that's possible.

Performance of 8.5x44 vs 9x63 vs 10x50


A higher contrast, sharper image from a smaller exit pupil can exceed an image from a larger exit pupil if it's not from an equally high quality binocular.

What do you give up to get 7mm exit pupils? Image size. But if the image is broad and diffuse, do you need a larger image scale? Maybe not.

The binocular that would be best for broad diffuse extended objects is not the same binocular that would be best for most other objects. For most everything else, a higher magnification (that produces a smaller exit pupil) provides a larger image and a bit deeper limiting magnitude that allows seeing more.

Think of the sky as the backdrop in a portrait. Your subject must stand out from the backdrop to be seen. (There must be contrast.) Consider it to be a grey scale. You all understand the affect of dark sky background. Higher magnifications in a telescope reduce the extended light of the background until it approaches a completely dark sky, to the point you can no longer see the field stop. Lower magnification with a larger exit pupil delivers more light, not only from your subject, but also from the background. This can be beneficial or detrimental, depends on the condition. Generally, this makes it much more difficult to see most objects, but in dark conditions may allow you to see nebulous objects.

Exit Pupil, Large or Small


There is no question that a larger aperture gathers more light. But it gathers not only the point source light, but also the sky background light. Under a dark sky, with far less sky background light, the performance curves are much further apart. Under a bright sky, the performance curves are almost equal.
But now on to (C), the most significant point Fiske highlights here. Let me repeat it.
(C)They (comparisons of performance as determined by point source LM) do not reliably represent performance on dim, extended objects. Try doing the 10x50mm versus 10x70mm comparison on a faint open cluster like NGC 7789 in Cassiopiea and see which instrument comes out on top.

This point cannot go overlooked. The difficulty is now involved in assessing which is better when viewing extended objects. This can be a subjective call. Point source LM is not subjective at all. However, it is not a good indicator of performance of contrast on extended objects.

There are a wide ranging class of objects that would fit the criteria "extended" in binoculars. Of course, all the typical extended nebula (Neb) and galaxies (Glx), but also some open clusters (OC). OC, if very dense may be resolved in scopes but may not be resolved in binoculars, and especially if comprised of predominantly faint stars. NGC7789 probably fits this criteria pretty well.

The difficulty comes in objectively assessing the performance on objects where you don't get a maximum or a count or something objective. This doesn't make it impossible to judge the differences in contrast, just more difficult.


Comment about Exit Pupil Size


"Contrast Enhancement via Magnification--As the magnifying power of an eyepiece increases, the amount of light reaching the eye decreases. However, a modest increase in magnification is often found to enhance the contrast between stars and the surrounding sky, and this effect can sometimes be exploited when making estimates of relative magnitude in moderately light polluted skies. It is frequently found, for example, that 10x-50mm binoculars are preferable to 7x-50mm binoculars in less than totally dark skies. The same holds true for a telescope, and you may find that an increase from a low power to a medium power eyepiece, say, from 20x to 40x, will provide a more favorable viewing situation under marginal conditions."
-- Sommers-Bausch Observatory -- University of Colorado:

"The glow of the background sky is a diffuse source, which will be spread out by higher magnification, reducing its brightness. Although high magnification doesn't increase the brightness of faint stars, it improves their contrast (ed. note apparent brightness, this article inproperly refers to this as contrast) against the sky, making them more visible!"

On the night sky, apparent contrast has *EVERYTHING* to do with magnification, light pollution, seeing conditions, surface light scatter, internal light scatter, quality & thoroughness of coatings, baffling, quality of optics, etc. In short, perceived contrast is a direct result of the summation of the whole instrument, the observing site and conditions and the observer.


edz






Edited by EdZ (02/13/10 07:15 AM)


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MEASURING / TESTING Optical Aspects of Binoculars new [Re: EdZ]
      #75703 - 03/21/04 03:30 PM

This first link is to one post that gathered a bunch of links as help to others who want to review the types of tests they can do to measure the performance of their binoculars. So go to this post and you will find about a dozen links to other posts, mostly here in the "Best Of" threads, on how to measure various aspects of binoculars.
Links for Aspects to measure as posted in the thread "Writing a Binocular Review"


Calculating TFOV

EdZ's list of sky distances for measuring True Field of View in binoculars
How To Measure TFOV Of Binoculars

Image Sharpness Across the Field of View
Another more 'full length' discussion of Filed Sharpness discussing a method how to measure accurately so binoculars can be compared.

Measuring True Sharp Field of View



Measuring the Magnification of your binoculars
Measuring the size of an exit pupil

Measuring magnification by observing a standard scale

Measuring Aperture by three methods
observing a scale in the exit pupil directly using a loupe
checking magnification then checking exit pupil
measuring projected image of a leaser thru the objective

this thread above has a great deal of information. For instance if you want to check aperture by measuring exit pupil, you must first verify the magnification. There are several methods to check magnification. They are also discussed in this thread above.

True aperture? A Quick Way to Measure!
Measuring effective aperture by the flashlight method. Simple and effective.
Flashlight Aperture Test Improved


and more on
Measuring Aperture, Illumination, Beam Tilt, Collimation
EdZ's 22 x 85 GO Signatures
This post contains essays explaining each of these tests outlined below
Checking aperture by using masks and checking exit pupil
Mask method explained in detail
Checking Illumination of the Exit Pupil (Beam Transfer) with a target laser
laser method explained with pictoral presentation
Results compared with a dozen other binoculars
Checking Optical Path Tilt with target laser
Using the Target Laser to guide adjustment of conditional alignment
The pitfalls of conditional alignment when some unknown cause of tilt is present.
A perfectly balanced binocular, The Fujinon FMT-SX 10x50 has full aperture, wide area of illumination, No optical tilt, and good alignment.


How to Measure Magnification and Aperture using masks
an example of the measurements that shows how this simple method works

Things to Watch Out for when measuring magnification

Excerpts from posts on explanations of how to measure magnification:

For magnification, see Henry Link's reference to Kimmo Absetz’s method of establishing a reading for a small power monocular:
Take a reading of a tape measure at some distance (75'to 100' away) using a monocular, then take a reading of the tape thru the binocular with the monocular behind the binocular eyelens. [Used a small scope to accurately get a measure on a scale about 100 feet away (reading approx 14-15 feet). Then used the small scope behind each binocular to take another reading and divided the two values.] Division of the readings gives the power. All magnifications reported here use that method. It gives a fairly accurate reading, but because of it's relatively close (100feet in my case) distance, all readings may produce magnification that is slightly (approx 1%) high. (In any binocular, Magnification varies usually by ~2% and by as much as 3%, from closest focus to infinity). However, anyone trying this method would see that it can be quite accurate and it is easy to measure power to tenths. Therefore, results are reported to 1/10th. All actual calculations produced values to hundreths, but there is no way that I can be measuring with that level of accuracy, so I have not reported it. It is impractical to measure using this method much beyond 150 feet and in fact impossible to test using this method at infinity.

OR

Place one eye to the binocular viewing a one inch blocked out (using 3M stickies) area on a scale and one eye looking at the same scale marked off in large blocks of inches, ie.' 7", 8", 10". Superimpose the images of the magnified 1 inch block over the scaled blocks (powers) of 7 or 8 or 10, whichever fits. It becomes easy to see them line up. If the magnified 1 inch block lines up with the 8" scaled block, it's 8x. I find it particularly easy when the magnified image falls in the middle of some colored sticky, showing for instance 8.5x. I can see powers down to an accuracy of about a quarter inch or 0.25x. Problem with this method is it needs to be done only at close distance, perhaps 20 feet to 50 feet at most. All binoculars increase in magnification at closer focus, so the result does not represent magnification at infinity, it represents magnification at some closer focus distance. But, since that close/infinity variation is perhaps only 2% to 3%, errors larger than that can be found easily. It takes some practice to let your eyes view two completely different images and superimpose them. I find it pretty easy to do.


OR

Measure the exit pupil as is at apparent full apereture. Record.

Assuming an 80mm binocular)
Then place a lens cap that has been cut to a 70mm aperture.
Measure the exit pupil WITH the 70mm mask. record
Then place a lens cap that has been cut to a 60mm aperture.
Measure the exit pupil WITH the 60mm mask. record
If I were using this method to test 50mm binoculars, I would test at 50mm, 45mm and 40mm.

You must measure exit pupil precisely to at least 5/100ths mm, so you need a precise dial or digital caliper. You would not be able to measure this precise with a $10 vernier caliper.
You must measure the mask precisely to at least one half mm.

Do the math for each aperture. The masks will show the point beyond which you have covered up all internal vignette and eliminate vignette from the equation. You need at least two measurements to agree.





How To Measure the Focal Length of Binoculars
Formulas you need to know and assumptions you can make if you want to estimate the focal length of your binoculars.
You must take into consideration the refractive index of the prisms.



Here's a simple test to compare Coatings from one model to another
Look for reflections in the coatings

See the "Best Of" post on coatings for much more.


Testing Edge Sharpness by observing double stars with known separations
Oberwerk BT100 - Stock 24.5mm ep sharpness
and Barry Simon tells us how he tests for edge distortions and Field of View in
Pop quiz: 22x100 Obe's or 20x77 Miyauchis



Deciding when it is necessary to adjust the collimation
Collimation

Measuring Eye Relief
and determining the difference between measured eye relief and usable eye relief


Exit Pupil, Brightness and AFOV
Does AFOV affect the brightness of the image in the exit Pupil?
How to test the Illumination of the Exit Pupil

Brightness in the Exit Pupil

and please excuse that I borrow this from another forum but here is an excellent discussion on
Thoughts on exit pupil, brightness, and resolution
it actually discusses the measuring of brightness in the exit pupil


Edited by Richard McC (03/22/12 06:17 AM)


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Best binocular overall or in a given price range new [Re: EdZ]
      #153415 - 07/22/04 11:36 AM

There's a lot of opinion about what's best, but this thread highlights links to some very good choices and makes a few good points for the buyer to watch out for.

In this link you will find a well organized presentation of suggested binoculars put together by Mike Swaim. While originally prepared for the purpose of recommending to beginners various binoculars for specified use or price ranges, Mike's gathering and organization of information leads us to a collection of short reviews within product lines. Mike touches on over 30 different binoculars in this very worth-while post that groups binoculas by powers and by price ranges. Along the way, he explains a few simple things the beginner needs to know when shopping for a good first binocular.
Light Trap's beginning binocular suggestions


Best all purpose binoculars for under $100


And this thread dedcribes one user's approach to "inexpensive" <$100 binos.
Got my Skymaster's



Several recommendations here lead the buyer in the direction of how to get the most for a $400 budget. Is that $400 just to buy the binoculars or to buy the binoculars and a good sturdy mount? How much binoc and mount can you get together for $400???

$400 Budget What do you recomend?


On a similar note this forum participant has outlined his process for making a decision on which criteria mattered most in his decision for an under $500 100mm binocular
The 100mm bino market in the $500 price point


This poster started out by stating "My budget is about $700 for bino's & mount". You'll soon find that forum participants here love to spend other peoples money. In the thread "So many topics & STILL no definite answers" we give our suggestions ranging from $425 for a used Fujinon 16x70 to a discussion about the $1500+ Oberwerk BT100.

$700 for bino's & mount.


Now, if you like premium optics in small packages here is a comparison of two premium Nikon 42mm optics

$800 to $900 buys Nikon premium 42mm binocs


Several Top of the line 12x50s Nikon, Leica, Zeiss
Strengths of Nikon / Leica 12x50s to a potential premium 12x56


Here's a good question. It asks whether or not it's better to spend more on a higher priced 16x70 or a lower priced 20x80 that might just be able to "beat out" the 16x70 in certain observations. And if that's true, why spend more?

Which of these tripod-use binoculars would you judge most likely to deliver the best performance in center field resolution, contrast and limiting magnitude: Fujinon 16x80 or a generic 20x80 like a Burgess LW, Anttlers or Barska?
16x70 Fujinon or 20x80 generic?
Contrast is the one characteristic of the view that you can't tell by the numbers. It is almost always increased in quality instruments and is lesser in bargain instruments.


And finally this thread has a very good discussion on high priced but superior quality binoculars. This is not best bargain in a particular price range. This is a discussion of what our members feel is the BEST out there.
What is the Best Binocular for Astronomy?



Edited by EdZ (02/13/10 09:35 AM)


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Favorite Binoculars in Various Sizes new [Re: EdZ]
      #153416 - 07/22/04 11:37 AM

The following post includes some excellent binocular choices and some all around good advice. It is worth the read.
"This list is NOT a "best of" list. Nor is it all comprehensive. It's not even a list of all the binoculars I've owned, much less tried. This list IS an attempt to give people some idea of where they might want to begin their shopping." - Mike Swaim
Mike's Recommendations - And Sound Advice


"Let's say I got wiped out by fire or theft and got an insurance check to replace the 15 pair of binoculars that I now own, what would I do? Here is what I would get (from top to bottom)." - Barry Simon
Barry Simon's List of Favorites


"while I have 150 models in my cabinets, that doesn’t begin to scratch the surface of what’s available. I do have a right to discuss what I own or use." - Bill Cook
A few of Bill Cook's favorites


"Just another opinion: I'd may well get the binos I have now." - Stephen Tonkin
Stephen's Short List


Various members here respond with a list of their favorites in Bill Cook's Favorites
Holger Merlitz, EdZ, Bill Cook, Kenny J.


Edited by EdZ (02/13/10 09:34 AM)


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Affect of Eye Pupil on Binocular Aperture new [Re: EdZ]
      #153417 - 07/22/04 11:38 AM

Affect of Eye Pupil on Binocular Aperture THREAD

A complete explanation of why you should take into consideration the maximum dilation of your own eye pupils before you consider what size binocular to purchase. This explains the implications of using a binocular with exit pupils that are larger than your eye pupils.

In a nut shell, if you are using a binocular with a 7mm exit pupil, for example a 10x70, but your eyes dilate to only a maximum of 5mm, then your binocular is effectively performing as if it were 10x50. You gain no more light gathering, brightness or resolution than the maximum exit pupil allows. In this case the maximum exit pupil is controlled by your eyes and would be limited to 5mm.

A collection of my various posts on this topic and predominantly modified and corrected to the information in the thread above led to publishing this article

Affect of Eye Pupil on Binocular Aperture CN REPORT

This information is just as relavant to a telescope user who is attempting to maximize brightness of image by using the largest possible exit pupil that the equipment on hand will allow. In the same manner as stated above, if the exit pupil exceeds the maximum dilated eye pupil, then you are reducing the effective aperture of the scope.


A member asked "I think these are great binoculars...BUT... I find they amplify sky glow or produce it? ... Is this because of the rather large exit pupil(7.1mm)? I don't see this glow in my 15x70's and I'm guessing that it's because of the 4.4mm exit pupil or the higher magnification." Binocular newbie confusion about Exit Pupil
This reply addresses both too large exit pupil, which can generate washed out images, and also too large eye pupil which can decrease effective aperture.



edz

Edited by EdZ (02/13/10 09:33 AM)


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Philosophy and Binocular Ownership by Bill Cook new [Re: EdZ]
      #194850 - 09/12/04 03:30 PM

And even more thoughts of philosophy, quality and ownership
Bill Cook on Binocular Ownership - 2012

More thoughts and philosophy on quality and binocular ownership
Bill Cook on Quality - Feb 2010

Optics Philosophy, Product Info and the very personal aspects of Binocular Ownership

We are reminded of some important things we should remember regarding the industry and the rags that tell us about the optics and how they perform. Thanks Bill.


this post by infrequent participant, but always well versed, Fiske, lays out
10 Reasons to Spend $1000 on "Little" Binos.
Certainly not for everyone, but it is a philosophy on ownership, for some, that is stated very well.



edz


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What can be Seen in Various Sizes Binoculars new [Re: EdZ]
      #200431 - 09/19/04 06:21 PM

This post collects a summary of the views of a selection of items through various sizes of binoculars from 10x50 all the way up to 22x100s, 25x100s and a BT100 binocular telescope with changable eyepieces from 24x100 to 62x100. It is not intended as a post on the differences in quality between binoculars. It's intended to give an indication of the differences in the VIEWS between various sizes.
Next BIG Binocular, How BIG!


More Comparisons
Observations and Comparisons with 8 Binoculars from 8x56 to 44x100

Here's the record of a handheld observing session with nikon SE 10x42s
Binocular Serendipity

Here's a report from a viewing session with Oberwerk 25x100s
A cool August night with Oberwerk 25x100s

Views of globular cluster M26 Scutum and Planetary neb M57 Lyra
Several small binocular handheld observations and several mid-larger binoculars on the same objects


Deep Sky Observing with 70 , 80 and 100mm Binocs
Galaxy Hunting with Oberwerk 25x100


What can be seen with 16x70s?--a report
Some of these objects are a struggle for a 20x80 or a 25x100. But in this observing session under dark skies you can read what can be seen in ~mag 6 skies.


The lowly 15x70 Skymaster under really dark skies
A very nice observing report using a binocular we often refer to as lower on the scale. But you will see from this report, they are very capable.


How many stars should I be able to make out in the Trapezium through 11x56 binoculars?
For the answer to this question, see the discussion here
The Trapezium in Binoculars


and this exceptional observing report using 8x42 binocular
Finally a few steps up the Bortle scale.
the advantage of a very dark site cannot be overstated


What Binoculars for Viewing Planets?
Here are some good summaries of various sizes of binoculars and magnification that will allow you to observe some of the phenomenon that we look to the planets for. Disks, rings, moons, phases, shadow transits.


Surface Brightness (Sb)
Observing faint extended objects such as galaxies is complicated by the fact that books generally list the visual magnitude, but a better indicator of whether or not the object might be seen is Surface Brightness (Sb). Read this brief explanation.

Visual magnitude of an extended object would be the magnitude if you could compress all the light of the object to a size of 1 arcminute area. Surface Brightness of an object gives an indication of how spread out the light is and how faint it will really appear.

For an object like M101 that has a visual magnitude of mag 7.7, but an area of diameter 26 arcminutes, that light is spread out over 530 square arcminutes. Hence is has a very low Sb = 14.7. That is averaged. As you get out towards the extremities, it is fainter, in towards the center it is generally brighter. So for instance a galaxy with a bright core might be visible, but it would appear much smaller than its full size because you can see the core but not the extension.

M101 has some brightening towards the core, so the core area actually has a little brighter Sb than 14.7, while the extremities have a fainter Sb than 14.7. Another example is M33 in Tri at Sb 14.0 was easy, this one also has a broad brighter core, so in these cases we generally see just the brighter core area.

Take the example of a DSO listed as visual mag 7. If the object is 10'x10' then it has an area of 100 sq arcmin. The light would be spread over an area 100x greater than the compressed area used to determine the visual magnitude measurement. It would actually appear 100x fainter than the visual magnitude. A light difference of 100x is 5 magnitudes so the Surface brightness of this object would be Sb = 7+5 = Sb mag 12.0.

edz



These records above of what can be seen in various sizes is all well and good, but let's not lose sight of the simplicity of binocular viewing. Here's a post from a thread titled What's Your Use for binoculars?

Few people claim to be able to hand hold 15x70s. Although I rate a pair of Oberwerk 15x70s or my Fujinon 16x70s near the equal of a low power telescope, I am not among those that can hand hold such a size and I use these sizes mounted. So I will relate to you how I grew to enjoy binocular astronomy with my handheld Orion 10x50s.

Many a night I would gaze upon clusters such as the Pleaides and the Hyades. I learned intimately the positions of the stars that make up these wide asterisms. I would spend evenings lying about searching out all the globulars I could find. In a night M3, M92, M13, M5, M10, M12. On another night M4, M22, and all the populated open clusters of Sagitarius. The M24 star cloud, then afterwards M16, M17 and M18 all at once.

I found M33 in my 10x50s for the first time after looking for months using a scope. I learned then that exit pupil sometimes provides for the best view, not power.

Countless open clusters, some in areas of the sky that take on a whole new perspective when viewed at wide low-power views, like the Monoceros area, the Cygnus/Vulpecula area and Sagitarius.

Along the way, I learned star patterns much better than I ever had just using a scope. Afterwards, I could starhop navigate some areas by sight alone.

Double stars do not escape my binoculars, although at 10x the views are just the wider ones about 20" or more. But dozens upon dozens of doubles, not just the Alcor/Mizar or alpha Capricorn wide doubles.

Nebula seem to jump out in binoculars, more-so than in a scope. M27, M16, M17, M42 in the smaller binocs, but even more in larger binocs.

Of course the Milky Way, especially thru Cygnus and Perseus, in binoculars is a sight to behold, especially the densely populated rift thru Cygnus.

And back to open clusters, those in the Milky Way fields thru Auriga and Gemini, M38, M36, M37 and M35 are outstanding even in 10x binoculars. Or the fields thru the Cassiopeia / Perseus border, where near delta Cas you can see four clusters at once near M103 then just nudge little by little your way thru the area of Stock 2 and the Double Cluster, a beautiful contrasting pair.

Galaxies do not escape the 10x binoculars. I've viewed M81/M82 as a pair and even spotted M51 with 10x50s. Numerous others make it a tour thru Ursa Major, Canes Venatici and Coma Berenices. You can't pass by here without stopping to view Mel 20, Berenices Hair.

All along the way you get to see the patterns of the constellations as if you were traveling the map of the constellations in a chart book. You will pick up so much more than you ever could with a scope, you will gain a new appreciation for the patterns in the sky.

And all that with 10x50s.

So, what I use my binoculars for is to view the sky in a more intimate way, with a lot less work than any scope. Maybe the key is to just let your eyes learn how to see on a different scale.

edz


Edited by EdZ (02/13/10 07:30 AM)


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Depth of Field and 3D or not 3D! new [Re: EdZ]
      #278014 - 12/10/04 06:36 PM

Depth of Field is the range of objects from foreground to background seen in focus at once without moving the focus dial. For instance a narrow depth of field might be all objects in focus from 30M to 50M. A wide depth of field might be all objects in focus from 15M to 75M.

This thread, once you read down into it, lays out some of the mathematics behind depth of field in binoculars. It started out with various users, including me, simply stating what we felt controlled DOF. Later on it gets into the real definition of how depth of field is determined.

Depth of Field start of thread
Read the posts by Jean Charles, Henry Link and Holger Merlitz
here are some extracts of the most important points

Quote:

I suppose that z is the distance at which objects appear sharp to the naked eye at the same time that objects at infinity.
M is the binocular magnification
d is the distance at witch the binocular is perfectly focused.
Without accommodation of the eye, we can see objects perfectly sharp at the distance d'.
By definition, the depth of field is (d – d').
Now, if I suppose that the exit pupil is always larger than the eye pupil, I find the equation :

1/z = M².(1/d'-1/d)

.....So, the only optical parameter which determines depth of field is the magnification. Its influence is huge, because of the 2-power of M in the equation.
Now, why people find that binoculars with equal magnification have quite different depth of field ?
I think that the perceived depth of field in binoculars is determined by other parameters than optical ones.
JCB





Quote:

focal length has almost none impact on the DOF. It is the magnification which dominates.

In summary it seems to be that only magnification and effective exit pupil are dominating factors for DOF. Focal length has some influence but not much. However, I am not sure how well the assumptions made for these calculations are satisfied. For example, a binocular is not made of thin lenses. Only professionals may be able to figure out the validity of these assumptions, maybe with the help of ray-tracing software.

With regards,
Holger





Quote:

The results can be found with the formula I wrote in a previous post :

1/z = M².(1/d'-1/d)

Here d is infinity, z=b , M=V and d'=G.
We have therefore : b=G/V² which is nearly the same as the formula on your post, in which the negligible terms have been omitted.
(For V=10 and G=100000 mm, we find b=1000 mm)
My formula is not rigorously exact, but is more general because it is also valid when the binoculars are not focused to infinity, but to the distance d.

I think it's worth doing some applications of this formula :
We suppose that the binoculars are focused to infinity, and that with naked eye we can see sharply objects without accommodation if they are 1 m away. Then DOF are :
For a 7x binocular : 49 m to infinity
For a 8x binocular : 64 m to infinity
For a 10x binocular : 100 m to infinity
For a 12x binocular : 144 m to infinity
People more than 60 years old, lacking in eye accommodation, and who have to rapidly focus between two distances (like birders), have to very carefully examine the drawbacks of high power binoculars, considering their poor depth of field.

Jean-Charles







Often associated with Depth of Field discussion is what is known as the 3D effect. So, here is some discussion about 3D, what is seen, what cannot be seen and the mathematics related to how things seem to have depth of field or appear 3D.
3D or not,3D!

Binoculars with a greater objective lens separation WILL provide more depth perception than a binocular with a lesser separation, regardless of the prism types . . . PERIOD!

the separation between objective lenses is the most important factor: a Porro 8x30 will show more 3D view than a roof 8x30.

Magnification has effect on 3D view, a greater magnification increases the compression of the fields reducing the 3D view: a roof 10x30 will show less 3D view than a roof 8x30.

Also distance has a significant impact on the so-called 3D effect;

For a binocular with objectives 150mm apart, observing two objects placed at

10 meters and 12 meters distant, the angles of view (with reference to centerline) would be 26 arcminutes and 21 arcminutes, a difference of 5 arcminutes, easily perceivably by the human eye.

100 meters and 120 meters, the angles would be 2.6 arcmin and 2.1 arcmin, only one half arcmin difference or 30 arcseconds. Already this narrow angle is beyond the perception of the human eye.

But if the objects were at
1000 meters and 1200 meters, the angles are now 0.26 arcmin and 0.21 arcmin. The difference in these two angles is merely 3 arcseconds, not only beyond the ability of the human eye, but beyond the capabilities of diffraction limited optics smaller than 46mm.

Curvature and Depth of Field
Here's a discussion why some binoculars appear to have a greater depth of field than others, even when the lens equations won't account for any difference in depth of field. As noted above, there is more to perception of depth of field than just mathematics. In this case a strong correlation is shown between the aberration Field Curvature and Depth of Field. A lens that has strong Field Curvature has a shorter focal length in the center and a longer focal length towards the edges. This has the affect of making closer objects apppear in focus if the center is focused on a distant object and the closer objects are viewed further out in the field of view. Hence the binocular has a greater depth of field, but only for nearer objects.







Edited by EdZ (02/13/10 09:30 AM)


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BINOCULAR OBSERVING REPORTS AND TARGET LISTS new [Re: EdZ]
      #278017 - 12/10/04 06:42 PM

Binocular Observing Reports Thread Links
This link was set up so all members could add links, all in one thread, to their own observing reports. By linking here to that thread, we've got a permanent access for you to get back to the thread that shows all of our Observing Reports. We add new links to new Observing Reports in this post. Here you can access the many Observing Reports from our members.


Now that the above thread handles all the observing reports, the rest of the links here will be to Observing Lists or links for lists. edz 7-19-07


Preparing to Run the Messier Marathon?
Messier List with 20x80 binos?
here's a list of links to various Messier discussion threads


Links to Moon Maps

Observing Satellites

Check out this interesting thread
unusual use for binoculars

Links to Sattelite Observing - TiPS


DEEP SKY
Binocular Deep Sky Objects in Groups
a list of 100+ objects in about 40 groups, generally seen in binoculars in groups of two or three together. Like cluster pair M46 and M47 or galaxy three-some M65-M66-NGC3628. Some notes included giving an idea how much binocular it will take to see the targets. Also, some links to charts.


DOUBLE STARS
Binocular Doubles Seen in Pairs and Binocular Doubles within Clusters
about 30 doubles for various sizes binoculars, uniquely identified with another as a pair of doubles or apparent as a double within a cluster.


Binocular Doubles - List of about 75 Doubles showing magnitudes and separations
While the Trapezium is probably the most famous and decidely one of the most interesting multi-star systems to observe, there are many other double stars that can be observed with binoculars. This list has grown from the original list of 60 to about 80 doubles for binoculars. Some are very challenging even for large 100mm binoculars with variable power eyepieces.

Faint Binocular Doubles
a list of twenty mag 7, 8 and 9 near equal pairs, mostly for 20x80 or larger binoculars. Probably 5-7 for 15x, 12x and 10x binoculars.


How many stars should I be able to make out in the Trapezium through 11x56 obies?
For the answer to this question see the discussion at this link to the Binocular Forum
The Trapezium in Binoculars

More info on the stars in the Trapezium



Challenging Doubles for High Power Binoculars doubles mostly from 10" to 7"

Ten Binocular Doubles seen with 15x70s


COLORFUL DOUBLES

Ten Easy Colorful Double Stars see spreadsheet attachment

Common Doubles with Significant Color Contrast

THE SEARCH (for colorful doubles) GOES ON a list of 20 Doubles





LIMITING MAGNITUDE M45 - Binocular Observing Chart
See if you can observe stars down to mag12 using this chart and a table of over 250 identified stars. There are some asterisms identified on this chart. They are referred to in the post above "Binocular DSO Groups".



SURFACE BRIGHTNESS
The ability to Observe Deep Sky Objects will not always be indicated by the magnitude of the objects. For extended objects, Surface Brightness comes into play. Visual magnitude (Mv) of a deep sky "extended" object is almost always NOT the appropriate measure of how faint an extended object will appear. Determining which faint extended objects, such as galaxies, might be observed is complicated by the fact that books generally list the visual magnitude (Mv). That would be how bright the object would appear if all the light could be compressed in a small spot only 1 sq arcmin. More often, a better indicator of whether or not the object might be seen is Surface Brightness (Sb), which is usually much fainter than Mv, and even that can vary. Read this brief explanation.
See a preface on Surface Brightness in
Deep sky limits on 25x100s



Some Notes on Surface Brightness
If you took an object that is mag 8 visually (in a 1 arcmin area) and you spread the light out over an area of 10x10 arcminutes, or an area of 100 arcmin sq, then the Surface Brightness (per area) would drop by a factor of 100x from the visual magnitude. That equates to a drop of 5 magnitudes or now Sb=13. But few objects have equal brightness gradient over the full diameter. So, while we could say the entire object area aveage Surface Brightness = 13, if there is a brighter core, say Sb10, then the outer fringes might be Sb16. So usually we see only the core, and even then, that depends on the Sb of the core.



Does aperture rule in bino land?

Deep Sky Observing with 70 , 80 and 100mm Binocs

Tonight's objects with 25 x 100 IF Oberwerks

edz


Edited by EdZ (02/13/10 07:28 AM)


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Fixed Focus Binoculars new [Re: EdZ]
      #283112 - 12/16/04 12:08 PM

Bill Cook explains the facts behind fixed focus and what value or what little value they really offer.

Fixed Focus Binoculars

Edited by EdZ (02/13/10 09:29 AM)


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Handheld Binocular Observing new [Re: EdZ]
      #294119 - 12/29/04 07:30 AM

What are the Issues with Handheld Binoculars?
Handheld Binocular Observing Issues
not only weight, but magnification is a major issue


Resolution mounted vs handheld
This is a resolution comparison of four binoculars; a 15x70, a 12x50, a 10x50 and a 8x42. I wanted to find out how resolution changes for mounted binocular versus a braced supported binocular, braced elbows and un-braced handheld.


Small Binoculars - Resolution
here's a list of 30 small binoculars from 7x to 12x. Both the best mounted resolution and the best hand held resolution are lists. Also listed is the percent drop in resolution from mounted to handheld. It's pretty consistent. Two thirds of all binoculars tested dropped 40%-50% in resolution when hand held, and the rest were either a step above or a step below that range.


50mm Binoculars handheld vs mounted
Here's a few comparative notes out of some recent observations. Here you can compare, first the difference in what a binocular can see handheld vs mounted and second, some differences between 7x50 and 10x50. Finally you can see a difference between the two 10x50s.



How to Hand Hold a Binocular
This thread has some users notes on methods for best results

Handheld holding technique to dampen vibration?

But visit this site by forum member Stephen Tonkin for the best explanation of various hand holding techniques

How to Hand-hold a Binocular


Edited by Zdee (06/27/12 07:57 PM)


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In Pursuit of Cheap Binoculars. What to Expect. new [Re: EdZ]
      #295344 - 12/30/04 12:07 PM

From time to time we go through this. It is generally a hard lesson for people to learn, but with few exceptions the results are usually the same. You get what you pay for.

Don't expect much from an $11 or $29 pair of binoculars when that cost is not much more than what it might really cost to just produce the objective lenses. When you think about it, binoculars are a complex instrument comprised of aligning the light path from the objective thru a pair of prisms on each side and keeping it all aligned as it passes thru two eyepieces and enters two eyes. How many of you purchase $11 eyepieces for your telescopes?

So just to remind you of the "you get what you pay for" mantra, here a a few of the recent adventures of some on this forum. Are you feeling lucky?

edz

Meade TravelView for $24.99 just remember to keep your receipt!


Barska 15x70 Nightmare a deal is not always what it seems.

good price on Meade Tarvelview not when they end up in the garbage!

Mixed opinions about these from various users More on the Meade Travelviews. Some won't go this route at all but a few people who have done so got lucky and are happy.

Meade Travelview 12x50 for $19.99 any thoughts? Most users thoughts are, if you don't expect much you won't be disappointed. As some who have gone this route point out, it's pretty much hit or miss.


Super Zoom 20-125x binoculars !

Cheap zoom binculars?
"would they be any use"?
"Oh definitely -- as paperweights, window ornaments, something to hurl at the neighbour's dog when it attempts to foul your lawn ... but not as an optical instrument". Stephen
"AND, if they very expensive ZOOM binoculars, just expect them to be expensive junk". Bill


Things to watch out for in cheap binoculars


Edited by EdZ (02/13/10 09:27 AM)


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Testing Binoculars in the Store Before Buying new [Re: EdZ]
      #311914 - 01/15/05 09:29 PM

We got this question not long ago from an interested forum participant.

“I was wondering if someone could point me to a web page that describes how to adequately test binoculars in a store before buying?”

Lots of people responded. This is a collection of the advice that was given. There was other discussion.. You can see the original thread here.
Binocular Testing

There is no doubt that some things cannot be checked in a short period of time. Personally, I'm of the opinion that to check out a binocular takes weeks of use. Some things just don't come out at you until you've used it for a while. It takes quite a while to really evaluate a pair of binoculars.

If you are looking at binoculars for astronomy, then I think a respectable business would provide a means for you to somehow have a look at night.

I think the best you can do in stores is to judge the brightness and resolution and to see if the ergonomics are to your liking. A $1 bill taped to a wall 15 ft or more distant can be a way of checking resolution. Larger binoculars like 12x50 need about 25 feet, 15x70 need 60 feet and 20x80 might need 100 feet.

Look at some reflections of lights in the coatings. In the objective lens you should see several reflections and ALL of them should be color reflections, none white. Generally a white reflection indicates some uncoated surface.

Better coatings reflect less light back at you. Look for coatings that reflect the least amount of light back.

Look down inside the binocular through the objective lens. In the circular metal ring that surrounds the prism face, you should not see any prism edges exposed in better binoculars. Also you should not see any sides of the other prisms protruding into the light path. A very small clipping of the exit pupil is often seen in mid-priced binoculars.

Hold the binoculars 6 inches to a foot in front of you and look at the exit pupil, the little beam of light that comes out of the eyepieces. It should be perfectly round. If it is noticably misshapen (oval) in any way, reject it.

Look very closely at the exit pupil for any straight edges cutting into the round exit pupil. Extrememly small edges cut off of the round exit pupil won't do much harm, but in a premium binocular reject any with big edge cuts.

Once more look at the exit pupils. If you see a diamond shape around the exit pupil where the light is dimmed in the diamond shape, these are Bk7 prisms. these will probably show the dimmed view in use.

Check to see if the binoculars can come together narrow enough for the width of your eyes. Inter-pupilary distance, IPD, can range from 52mm to 78mm on some binoculars, but on others only 60mm to 72mm. If you have eyes that are set apart by only 56-58mm, you must spend the time to find a binocular that adjusts narrow enough to fit. If you are endowed with a large nose, you may need a binocular with a very wide setting.

If the binocular is to be used by children as young as 7 or 8, the IPD will need to accommodate very narrow set eyes. Of the hundreds of young kids that I've had out to view, quite a few had a problem at 59mm IPD (Orion Ultraview, Minolta Activa), most were served well with a 57mm IPD. Only very few need a binocular with IPD narrower than 55mm. Two young 4th grade girls out of 13 kids in my recent class needed less than 55mm.

Press against the eyepieces while holding them up to your eyes. If the eyepieces are loose and move in allowing you to change the focus, reject that binocular.

Make sure the right diopter has enough range to accommodate your prescription. Some binoculars do not have enough right diopter adjustment.

Look AT the edges of the body outside of the front objective lens. Look to see that both objectives are recessed from the front of the binocular by the same distance. If they are substantially different it will throw off the diopter settings when you focus and you may not get the use of all the diopter adjustment that you need for your eyes.

Focus at some distant sign. Check the image across the field of view, not only at the very center of the field, but also at the edges and midway between center and edge. How does the image look, clear and sharp or blurry? A binocular should have at least 60% to 70% of the central view clear and sharp. Any less and I would reject it.

Edge sharpness of binos is quite easy to tell when you get a pair under the stars but difficult to evaluate when viewing cityscape in the daytime. Binoculars that seem perfectly sharp in daylight can have miserable off-axis performance on the night sky, even costly premium instruments. Pinpoint star images are a much more critical test for sharpness than anything that can be done in daylight.

Shake the binocular. If you hear anything rattle, reject it.

Must you wear glasses while observing? Check to see if you can observe the entire field of view with your glasses on. If not, there is not enough eye relief.

Even non-glasses wearers should check the eye relief. If you can't see the entire field of view without glasses, pick another binocular.

Observe some very high contrast object, like a black pole against a brightly lit background, or a white post against a dark background. Do you see a lot of color fringing around the edges of the object? Do you find it objectionable?

If you don't like the way a binocular feels in your hands, it probably isn't a good choice for you no matter what the specs indicate. One of the primary advantages of binoculars over telescopes is comfort and ease of use. No matter how outstanding a binocular is optically, if it isn't comfortable for YOU, it's probably not a good choice.

Lighter is not always easier to hold for longer. After you've tried a few different binocs, you will find some that feel good and some that feel not-so-good. Not-so-good will usually get worse the more you use them.

An outstanding binocular has to be excellent optically AND ergonomically.

I've never seen ANY daytime test that gives as precise a collimation check as does checking on a star. Checking collimation at 100-200 ft. is not the same as collimation at infinity.

Certainly you can give this a try. With you eyes about an inch or two behind the binoculars, allow your eyes to let the images in each side go loose and watch to see if they come back together or merge. If collimation is really way off, you can tell in an instant.

Move every hinge and turn every dial, feel for sticking spots. Any bad humps or real sticky spots, try out another pair.

Turn the focus dial so the eyepieces are half way out. Now grab the whole eyepiece bar assembly with your fingers and try to rock it. Does it require some force to make it rock, or does it seem flimsy and rock in and out real easy? Reject flimsy.

If you don't know the differences between what the fields of view (fov) are like, then you need to try about three different sized pair with different fov. Put one edge of your view on the exact same spot for each binocular and make a note of how far across the wall it can see. Compare with the others. Every 1° field of view is 1.75 feet across at a distance of 100 feet.

You can test for pincushion distortion on a distant high-contrast sharp line, distant TV antenna or power lines or a vertical post and moving it to the edge of the field. Look for a curve in the vertical or horizontal edge. This is not necessarily bad for astronomy, but might be a reason to reject if terrestrial use is your priority.

While looking through the binocular, see what other items are for sale in the store. If the shop is full of items such as thermos flasks, thermal socks, walking boots and cheap compasses, you are probably in the wrong store.

For waterproof binoculars, it can be very useful to take along a bucket full of salty water. Ask the assistant to dunk the binocular in it for 3 minutes. Then remove it and see if there are any signs of water ingress.

Edited by EdZ (02/13/10 09:26 AM)


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POLLS in Binocular Forum - take a poll new [Re: EdZ]
      #339414 - 02/10/05 11:52 AM

These links will take you to the several POLLS we have conducted here in the Binocular Forum. You can participate in the poll, or if you have already taken it, you can check out the results as of today. You may add comments/replies to the Poll threads.

Links to Future Polls will be added here.

edz


Poll: How many binocular forum visitors?
The binocular forum has a number of regulars. But, how many visitors do we get? Perhaps some non-members will join CN just to cast their vote. thanks, edz.
143 votes as of 6-3-08
160 votes as of 8-28-08


Poll: Binocs - Image Stabilized vs Conventional
What do you use for handheld? At what size do you use a mount?
118 votes as of 6-3-08



Poll: Did You Use our Best Of Forum Resources?
Share your opinion with us if you find the "Best Of" links useful.
32 votes as of 4-1-06
39 votes as of 4-24-07
43 votes as of 6-3-08
70 votes as of 8-28-08



Poll : Largest Handheld Binocular
98 votes as of 7-4-05
110 votes as of 3-17-06
122 votes as of 4-24-07
124 votes as of 5-29-07
141 votes as of 6-3-08
the next three sizes added together are still less than 10x50s

Poll : How Many Binoculars Do You Own?
128 votes as of 7-4-05
158 votes as of 3-17-06
173 votes as of 4-24-07
215 votes as of 5-29-07
285 votes as of 6-3-08
not surprisingly, most people own 1-2-3 or 4 pair.


Poll: What Size Binocular Do You Use Most Often?
151 votes as of 7-4-05,
the three most commonly used sizes in order are 10x50, 15x70 and 8x40/42
248 votes as of 3-17-06
261 votes as of 4-24-07
272votes as of 6-3-08
the three most commonly used sizes in order are still 10x50, 15x70 and 8x40/42


How Big are Your Eye Pupils?
71 votes as of 7-4-05
80 votes as of 3-17-06
84 votes as of 4-24-07
91 votes as of 6-3-08
most people who responded picked eye pupils 6mm or larger.
Hmmm, not the typical bell curve results we would expect to see.
Also sort of flies in the face of decades of medical studies. salt anyone.




Edited by EdZ (08/28/08 11:34 AM)


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Binocular Vision Summation - Two Eyes vs One Eye new [Re: EdZ]
      #339415 - 02/10/05 11:53 AM

Quote:

This is your first stop for a comprehensive explanation of Binocular Summation, how binoculars, telescopes and telescope/Binoviewers all compare and the benefits that can be derived from each.
Binocular Vision Summation
This comprehensive thread includes a compilation of all I have written on Binocular Summation. In addition several noteworthy posts by other members add some imporant information on vision.

Northeastern State University College of Optometry, Tahlequah, OK
Vision Science course module by Thomas O. Salmon, OD, PhD
Vision Science Home
Salmon's Current Lectures
Old Lectures - Binocular Vision Series
Lecture 10 Binocular Summation


Predicting Binocular Visual Field Sensitivity from Monocular Visual Field Results
(Investigative Ophthalmology and Visual Science. 2000;41:2212-2221.)
© 2000 by The Association for Research in Vision and Ophthalmology, Inc.
Jacqueline M. Nelson-Quigg1, Kimberly Cello1 and Chris A. Johnson2
1 From the Optics and Visual Assessment Laboratory, Department of Ophthalmology, University of California, Davis; and 2 Discoveries in Sight Research Laboratories, Devers Eye Institute, Legacy Health Systems, Portland, Oregon.







Older threads that helped generate some of the information that eventually got included above.

The question gets asked, "What scope would provide the equivalent of the view thru a given size binocular?" You will find the answers here. Along with that you will find some links to some great information on the internet that will help you understand the concept of Binocular Summation. Also see the thread here at the top of the binocular forum that provides links to internet articles for more links to info on binocular summation.

Informal Shootout: 5" APO vs. Saturn III this more recent thread covers the topic in detail

Binocular Summation - Aperture Equivalency
This thread discusses what equivalent aperture would be needed in a mono view scope to produce the same amount of light and contrast as a binocular.


Binocular vs Binoviewer
in this thread the comparison takes a twist. Comparing to a binoviewer, you need to account for beam splitting and then the resultant binocular summation in the binoviewer.

This new thread Jan 2007, gives data collected from three different models binoviewers and shows how clear aperture restricts field of view. A summary is given for lowest power acceptable field of view for binoviewers and then that is also give as a binocular equivalent.
Binoviewers and Binoculars (equivalents)

Wikipedia explanations of Binocular Summation


Edited by EdZ (02/26/11 07:56 AM)


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Binocular Photo Gallery new [Re: EdZ]
      #388157 - 03/28/05 11:05 AM

This is a collection of Binocular and Binocular Mount photos posted by members who have established a Personal Photo Gallery and have linked their photos into the Binocular Photo Gallery


Binocular Photo Gallery

The advantages of posting your photos to your own gallery and designating the gallery they appear in as the Binocular Gallery should be readily apparent. There is no memory limit to posting photos in the galleries. Once posted in your gallery you can link to your photos from anywhere without the need to ever post your photo again. Once in the gallery, you can sort all photos by several criteria. You can respond to photos with your comments. They will never get lost in an individual thread, they will always be in your own persoanl gallery.

edz


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Binocular Deep Magnitude Observing Charts new [Re: EdZ]
      #427366 - 05/03/05 07:45 PM

These observing charts were created for studying limiting magnitude in binoculars and in small scopes. Some of the charts have from 100 to 250 stars labeled and identified with an accompanying table listing all the star magnitudes. Some charts go to mag 13.0, some only go to mag 12.5, but you will find that really goes deep for binoculars. As additional charts are developed they will be posted here.

edz

Chart of M44 to mag 13 (The Beehive)

no table of magnitudes yet for this chart


Chart of Cr399 to mag 12.5 (The Coathanger)

Table of stars with magnitude listed for this Cr399 chart


Chart of M45 to mag 13.0 (The Pleaides)

table of stars with magnitude listed for this m45 chart


Edited by EdZ (02/13/10 06:58 AM)


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BOOKS for Binocular Observers new [Re: EdZ]
      #462329 - 06/02/05 07:46 PM

This question came up recently and as I looked back through the forum history it comes up repeatedly. This space will soon be filled with links to all the great suggestions and book reviews provided by the outstanding contribututors to the binocular forum.

edz

the newest binocular book on the market
Binocular Astronomy by Stephen Tonkin
released December 2006. Stephen is a regular in the CN binocular forum, and a presence in Astronomy, earlier I'm sure, but at least since I've been reading his stuff on the web, since 1998. This book spans the spectrum from beginner to experienced binocular user.

single best book for a binocular astronomy beginner there probably isn't just one, but this thread will help you by asking what are your needs and will highlight a few depending on what they are, learning, deep sky, science or repair.

Well then, next clear night I'll point at Sagitarius. (Where is that, exactly?) A few suggestions to help you find your way around.

Southern binocular objects... need some ideas Carsten Doehring suggests The Observers Sky Atlas by E. Karkoschka


Binocular observing books? this thread is a goldmine of contibutions by many members of the forum. Books and Charts for observing.

I would give strong recommendation to two books.
I recommend both Craig Crossen's Binocular Astronomy AND Norton's Star Atlas, not either/or.

Crossen's will give you:
a selection of objects specific to both large and small binoculars;
some very good detail localized maps, but not a full set of charts;
an outstanding explanation of the structure of the Milky Way;
a presentation of astronomy by seasons;
some excellent black and white photos close to what you see thru binoculars.

Norton's will give you:
A set of full sky charts, the Bright Sky Atlas, but no localized detail charts;
detailed lists of objects on each of those charts, some beyond binoculars;
some excellent technical explanations of the physics of optics;
some excellent technical explanations of astronomy, galaxy types, star evolution, etc.;
some detailed moon maps.



Books for Lunar Observing

and

"Modern Moon"


Star atlases suitable for binocular astronomy


Binocular Stargazing "Reynolds gives a very good overview of binocular observing" but seems to be a little light on stargazing info.

Observing Lists
"110 extraordinary objects to see with an ordinary pair of binoculars"
This link, provided by John Flannery, from the Irish Federation of Astronomical Societies (IFAS). The binocular handbook features a half-page about each object along with a chart of the field. The introduction says that you must be a member of an IFAS club, however they dropped this requirement. Feel free to get in touch with any errors or comments. Also, the handbook can be freely circulated. See comments from the author here.




Technical References

Choosing, Using & Repairing Binoculars by J. W. Seyfried, president of University Optics. Has some good, but also some outdated, information on repair maintenance and adjustment of binoculars. Has good explanations and diagrams to help the amatuer understand binocular assembly and adjustment.



BASIC OPTICS AND OPTICAL INSTRUMENTS prepared by the Naval Education and Training Development Center. recommended by William J. (Bill) Cook, Chief Opticalman, USNR-Ret., Founding Editor, Amateur Telescope Making Journal
his comments on the book,
The book has a great section on understanding basic optics principles. Other than that, the very short bino collimation section may very well be all that interests you. It is full of metal work, what kinds of greases to use for this or that, and a bunch of boilerplate that pertains to Navy instruments that haven't been made in 40 years. Please keep in mind that the collimation section deals only with instruments that are collimated with eccentric rings.


MIlitary HandBooK 141 - Optics, Vision and Optical Design
this arrangement of PDF files is hosted by the University of Arizona and represents an immense resource on Optics and Vision.


Edited by Zdee (06/25/12 09:37 PM)


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Dark Adaptation, Eye Pupils, Lights new [Re: EdZ]
      #573393 - 08/25/05 10:50 AM

Red Light vs Green Light


Pupil Size


technical paper by C. J. R. Lord FRAS
a technical paper that plots reduction in percentage illumination as affected by eye pupil smaller than exit pupil and reduction in percentage illumination as affected by eye pupil larger than exit pupil.


technical paper on optics and vision
this in a huge reference work published by the DOD. Here is a link to the 630 page document hosted by UofA Optics Department


Poll: How Big are your Eye Pupils?


Edited by EdZ (02/13/10 06:48 AM)


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Chromatic Aberration, Triplets, Semi-Apo, Apo new [Re: EdZ]
      #662278 - 10/29/05 11:41 AM

CHROMATIC ABERRATION (CA)

Achromats and False Color Blur Circle

The visual appearance of the ratio of color blur is low limit eye dependant. While color blur is always larger than the low limit of the eye, the resolution disks are almost always limited by the eye. Therefore in all cases we need to use the low limit of the eye for resolution.
there is a lot more visible color in a f/4 or f/6 100mm binocular than there is in a 8x40 or 10x50 and to some lesser degree even a 15x70. That's because the combination of small aperture and low power has a dramatic affect on reducing color blur.
for any given aperture, higher f# (a slower scope) provides better color correction. Most knew that. But what is not so readily known is that small apertures have very little effect on false color, or color blur as it is referred to here. An 8x40 achromat binocular has the same color error as a 120mm ED scope at 25x. The color blur in a 7x32 or 8x32 achromat, although still not apo quality, is extremely good without any further manipulation of the optics, the 7x32 being better than and the 8x40 or a 120mm ED semi-Apo scope and the 8x32 being equal. It doesn't take ED glass in the 8x40 or 7x32 to get that low color blur ratio.




The most important thing the user should understand is that it is impossible to completely eliminate CA from a lens system. It can be reduced to an almost imperceptible level, but cannot be eliminated altogether.

This is an explanation of what chromatic aberration is and how it affects the overall image
Chromatic Aberration

This explains some of the math of CA
Chromatic Aberration on planetary disks

Chromatic Abberation is one of the least worrisome aberrations. In an astro binocular, it is only present in about 1% of the objects viewed. So it should be one of the least critical aberrations on which to base a decision. Judge your choice of binocular on all the features and known aberrations that make a difference in the view 99% of the time. Honestly, the planets are not binocular targets, so the moon is the only astro target that would be a consideration for judging whether one needs to consider CA in the choices of astro binocular.

For terrestrial viewing CA becomes an important factor. CA becomes a problem in extremely bright conditions, not in low light conditions. However, there are not too many people using 15x or 16x binoculars for terra viewing.

A Table Plotting Chromatic Aberration vs Objective Size and Focal Length
see this interesting post in the refractors forum that discusses CA.. From the post...
" It illustrates the relationship of aperture and f/ratio to displayed chromatic aberration in achromatic refractors. Roughly, telescopes with similar CA ratios can be expected to display similar levels of visual CA; as CA in achromatic systems is a function of objective diameter and focal ratio.

Using this chart, one can get an idea of how another refractor will perform based on the performance of whatever model one already has. "


See this thread for
A discussion of CA in premium and well corrected optics


A discussion related to chromatic aberration in several model binoculars took place embedded in this thread.
Obie vs Fujinon CA



-------------------------------------------------------------------------------

There are two different forms of CA

Logitudinal CA is caused by the fact that, even with precisely on-axis light, in the focused image from an achromat all the wavelengths do not have the same focal length. Typically light in the image of an achromat varies from blue to red focal length by 1/1800th to 1/2000th of the focal length of the objective lens. So, for a f/4 100mm binocular, the focal length of red to blue might vary by as little as 0.2mm. That may seem inconsequential to you, but that might represent a 15°-20° turn of a center focus dial on a binocular.

Light that is not focused precisely does not make the minimum sized point of light in the image. If the minimum diameter circles of light for each wavelength is at a slightly different focal length, that means when focused precisely at any one color (usually yellow) that the Airy disks of all other wavelengths (colors) have slightly larger sizes and they overlap the yellow image, forming CA in the on-axis image. This is not generally seen by the observer unless you slightly defocus the image. But rest assured it is there and it has an affect on contrast of fine detail. This may possibly be seen in the inability to bring the focus to a precisely small point of light. An achromat that is not corrected to even 1/1800th f may have a difficult time forming a precisely small image of even a moderately bright point source.


Lateral CA is caused by the fact that the light rays forming the image across the lens all have slightly different lengths to a focal plane but the focus mechanism wants to focus across a flat plane. For all the points of light in an image to be in focus at exactly the same time, our focus mechanism would be required to focus across a slightly curved image plane. That doesn't happen. Since the system is incapable of providing that precision, we see the light spread across that plane at varying amounts of out-of-focus.

If you were to draw several half inch wide concentric circles over the field of view, you would see that in the outer fov ring you see all one color, green, in the next ring in all another color, purple. The color you see is dependant on how far off-axis the image is in the plane. The further off axis, the longer the physical length of the light ray beam to the plane. The varying lengths of light rays causes each color to be out of focus more-so than some other color at different distances off axis. This form of CA is entirely due to where the light falls across the plane.

See this thread Question about CA....


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This comment recently generated a discussion about Achromat doublets, Triplet objectives, Semi-Apo and Apochromatic lennses, means of achieving better color correction or lower CA.

Quote:

I've learned what it means with telescopes that are Doublet and Triplet...but how is that terminology used for the 20x80 triplet bino's? are they true apo or semi-apo or something entirely different?




I answered:
I doubt you will find any binocular anywhere on the market that is a true Apo, whether it is labeled as such or not, unless possibly you are up in the range of several thousands of dollars.

The fact that it is a triplet should indeed lead to some degree of better color correction, but it is not a gaurantee. While it usually takes a triplet to make an Apochromat, triplet is no indication that any instrument, binocular or telescope, is an Apochromat. It simply means that a third element of glass is incorporated into the design to give a slightly better color correction. In a binocular, it is probably still an Achromat.

A typical Achromat has two colors corrected, usually red and blue, so their focal lengths will be within approximately 1/2000th the focal length of yellow. An instrument would need to be corrected to within 1/8000th to 1/10,000th the focal length of yellow to be considered an Apochromat.

Generally the term Semi-Apo is applied to instruments that have been corrected to within 1/4000th F. It is very likely some of the instruments on the market, both telescopes and binoculars, are not corrected to 1/4000th F, and yet are still called Semi-Apo. It could be these instruments are better than 1/2000 corrcted, perhaps 1/2500 or 1/3000. Frankly, any improvement over the level of correction of a standard achromat should be appreciated as it is not particularly easy to achieve and rather expensive to incorporate into the design. I would question if any of the triplet binoculars are reaching a level of correction to 1/4000 F.

ED Glass in Binoculars




edz


Edited by EdZ (03/26/10 01:38 PM)


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Resolution Testing and USAF Res Charts new [Re: EdZ]
      #662351 - 10/29/05 12:27 PM

Binocular Resolution Testing Using 1951 USAF Line Pair Charts
In addition to test results for about a dozen binoculars, this thread shows some comparative results for a very good semi-apo 80mm telescope. Also included is a discussion on how to use the charts and links to web access for the charts and tables.

See the chart and the tables in my gallery here
USAF 1951 Resolution Chart and Table of Constants
It is extremely important that the chart be exactly sized.
The caution here is the user must know exactly how to size the chart.
You will find sizing notes below in this post and also in my gallery.


Source for commercially available resolution charts
Edmund Optics


Conflicting Arcsecond Test Results Explained
an excellent discussion explaining the differences in various arcsecond resolution values posted various places around the internet, and how to interpret them. This discussion is relevant to understanding how to use the USAF resolution charts and how the values determined by using them is so different than point source resolution. It explains why resolution values determined by the USAF charts are significantly closer than can be achieved observing point sources.



Understanding Resolution
a comprehensive technical report on the various criteria affecting resolution


Double Stars for Binoculars - a list of doubles for all sizes from 7x35 to 40x100
a list of double stars from which you can select observation targets providing you with good indications of the maximum visual point source resolution of your instrument.



Quote:

Lens Resolution Testing
and a link to a USAF 1951 Chart with the Table of Constants.
Chart with Table of Values


I find it interesting that few if any current web links provide ALL the information necessary to use these charts.

Using this table of values linked here which shows the constants for the Groups and Elements of the Line Pairs Chart,
the forumula is 8121 / (D x LPM) where D is the distance to your target measured in inches and LPM is the value from the Constants.
The constants are the actual number of line pairs per mm for the mimimum you can see.
For instance a 10x binocular used at a distance of 125 feet that can see line pairs in Group-1, Element2 has a value of 0.561. Therefore it's resolution is 8121/(125x12x0.561) = 9.65 arcseconds.

Line Pairs Resolution CANNOT be directly compared to point source resolution. See the forum discussion.
It is extremely important to have the target sized properly. See the discussion in the forum thread.
Binocular Resolution Testing Using 1951 USAF Line Pair Charts
included is a discussion on how to use the charts and links to web access for the charts and tables.

It is extremely important that the chart be exactly sized. As a check, the three bars and two spaces in Group-2 Element 1 should measure exactly 10mmx10mm. Both the sets of bars in G2-E2 and the solid black square top center should measure 9mmx9mm.

This page was originally accessed from
http://medfmt.8k.com/mf/resolution.html
Lens Resolution Testing by Robert Monaghan
which has posted the following notation along with the information
[My understanding is that the USAF chart etc. is in the public domain as it is a government produced chart and related documentation...]






Edited by EdZ (02/13/10 06:42 AM)


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Limiting Magnitude and NELM new [Re: EdZ]
      #662356 - 10/29/05 12:28 PM

See also the Best of Thread on Surface brightness

Limiting Magnitude Articles and Resources


Limiting Magnitude tests on M45 - More than a dozen binocular sizes
this thread has links to charts fro M45, M44 and Cr399. it also has the record of the best observations I've recorded with dozens of binocular attempts at reaching BLM.

Bino Magnitude Efficiancy - Handheld vs. Mounted

Binoculars Limit Star Magnitude with Small Scopes Comparisons


Call for Participants in Binocular Study of M45
This post includes links to charts you can use on M45 and provides an explanation of this study.

Some results from the initial Limiting Magnitude Study and a brief summary of some of the factors that will affect LM results

First Study of Limiting Magnitude on Cr399


Limiting Magnitude in Binoculars - Lab Report by EdZ
Explains the importance of magnification to achieve limiting magnitude.

Naked Eye Limiting Magnitudes in Taurus
includes a broad selection of stars identified from mag3 to mag6.5

NELM chart Little Dipper and Polaris

NELM chart area around Sagitta, M27 and Cr399

NELM chart of Delphinus

NELM chart Circlet of Pisces

Binocular Limiting Magnitude chart to mag 13.0 in M45 - The Pleaides
includes Naked Eye Limiting Magnitudes from 2.8 up to mag 7

Binocular Limiting Magnitude chart to mag 11.0 in CR399 - The Coathanger
includes Naked Eye Limiting Magnitudes from 5.1 to 7.3

Binocular Limiting Magnitude chart to mag 12.5 in CR399 - The Coathanger
same chart as in previous, updated to include deep magnitudes for BIG binoculars 100mm and larger,
or for use in mag6+ skies where even 20x80 binoculars might be able to go deeper than mag 12.0


Limiting Magnitude chart of M44 - the Beehive magnitudes not listed but symbols provide a guide from brighest to faintest stars


This post in the binocular forum has links to the above charts, tables of star magnitudes for use with the charts and reports on some data collected with many binoculars comparing the limits of magnitude that can be reached with various sizes of binocs.
Limiting Magnitude Charts and Tables


Southern Hemisphere Several LM Charts


See these threads for discussions of Surface brightness

Does aperture rule in bino land?


Deep Sky Observing with 70 , 80 and 100mm Binocs

Tonight's objects with 25 x 100 IF Oberwerks

edz





Edited by EdZ (02/13/10 06:39 AM)


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Writing a Binocular Review new [Re: EdZ]
      #662359 - 10/29/05 12:29 PM

To have your review published in the CN Reviews (and not just posted here in the forums) attach a word document and send it to submit@cloudynights.com


How to Write a Binocular Review
this thread starts by explaining that format and grouping of content is important to get your point across. Then it provides a list of links for reviewing many of the aspects that can be measured and reported as important information in a binocular review.


This is a list of suggestions on aspects you can cover in a review
Topics List for a Mini Review
this thread contains the history of the start of the MiniReviews.


And this list prepared by Milt Wilcox,
Astronomical Binoculars Figures of Merit
is a another very good crib sheet of things to consider when writing a review.




Read the CN Editorial Commentary here.
It explains that CN as a whole wishes and strives to remain fair-handed in its reviews.


And see these brief guidelines for submitting a review to the CN Reviews
We ask all submissions to agree to some simple guidelines



Here is an article published in the CN Reviews on
How To Write a Product Review

The fact that some people question how or why they should attempt to write a review is not new.
Look at this discussion that took place well over a year ago.
Don't Forget How Cloudy Nights Got it's Start.

edz

Edited by square_peg (10/08/09 12:23 AM)


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Polish Binocular Tests and Reviews new [Re: EdZ]
      #857613 - 03/07/06 09:52 AM

These links have been moved here to their own library card, as previously they were buried in the Binocular tests link and were quite a bit more difficult to find. The resources provided here are far more worthy than to be buried somewhere.
edz 3-7-06

The following links to posts, compilments of Arek, are the shared information provided to the CN binocular forum on all the work that has been published in what we now refer to as the Polish Binocular Reviews. From Arek's first post on this subject, I'd like to mention that credit is due to the following organizations and people. thank you Arek. edz

Quote:

Our tests are made by the group of people connected with the Polish
Comets and Meteors Workshop (CMW), Nicolaus Copernicus Astronomical
Center in Warsaw and Warsaw University Observatory. The people belonging
to this group are: Michal Jurek, Lukasz Kowalski, Krzysztof Mularczyk,
Arkadiusz Olech, Andrzej Skoczewski, Konrad Szaruga Mariusz Wisniewski,
Kamil Zloczewski and Przemyslaw Zoladek. The typical test is made by
5-7 persons and their marks are averaged.





The first post is a list of tests and descriptions of what might be considered closer to labratory tests of binoculars.
Testing methods in Polish tests of the binoculars
the methods are those employed by a group of people mentioned above. Some of these procedures cannot be undertaken by the average observer without the use of digital equipment.

The actual reviews can be found here at this website showing the results of the tests

Arek has provided links here to a number of other reviews/test results

Arek has translated and posted some of these reviews here to the CN Binocular Forum. Rather than point you to each individual review, I will point you to a link page showing all of Arek's posts so you can search out any of those reviews you would like to read in english.

Also see this post for more comments on this work.please refer to this post about Polish binocular reviews for links to Arek's work.

Edited by square_peg (10/08/09 12:13 AM)


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Surface Brightness of Extended Objects new [Re: EdZ]
      #874516 - 03/17/06 04:00 PM

Surface Brightness of Faint Extended Objects

A Preface on Surface Brightness

Finding book references for Observing of faint extended objects such as galaxies is complicated by the fact that books generally list the visual magnitude, but a better indicator of whether or not a faint extended object might be seen is Surface Brightness (Sb). Even that is not the best indicator of how easy it will be to see as you will see. But at least read this brief explanation to gain some understanding of how Surface Brightness works.

Visual magnitude of a star has all the light concentrated to a singular point. Not so for extended objects. Extended Objects have varying sizes, some can be very large. Visual magnitude of an extended object would be the magnitude you would see IF you could compress all the light of the object to a size of 1 arcminute area, about the size of M57, the Ring nebula. Surface Brightness of an object and size together gives an indication of how spread out the light is and how faint it will really appear. An object that has a a Sb = 12.0 with a diameter of 10 arcminutes is going to be much easier to see than an object that has a Sb = 12.0, but has a diameter of 25 arcminutes.

The formulas we use to find what limiting magnitude an instrument might reach do not always tell us how well an instrument will perform on all types of objects, especially faint entended objects, which have a whole different set of requirements. While total light gathering (usually measured by limiting magnitude of stars) is important, to differentiate a low surface brightness object from the background sky takes good contrast.

If you have an object that is mag 8.0 visually (in a 1 arcmin area) and you spread the light out over an area of 10x10 arcminutes, or an area of 100 arcmin sq, then the Surface Brightness would drop by a factor of 100x from the visual magnitude. That equates to a drop of 5 magnitudes. Therefore it would have an average Sb of mag 13.0.

Likewise, if an object surface brightness is given as Sb 15.0 and its area is given as 17'x15' or 255 square arcmin, we can figure its visual magnitude for an area of 1 sq arcmin. What magnitude corresponds to 255x brighter? Well its easy enough to get to 250x brighter. 100x is 5 magnitudes and it's 2.51x for each magnitude, so 251x is almost exactly 6 magnitudes. So 255x the area would be close to 6.0 magnitudes difference. Of course, you could never condense the object to a size of 1 arcmin, so it's not as useful to calculate Mv. It's much more useful to have Mmv given and know how to calculate the fainter Sb.


edz


See these threads for discussions of Surface brightness
Does aperture rule in bino land?

Actually no it does not. Dark Skies Rule. Here's Why
An offsite paper by Bill Ferris explaining contrast threshold
Lowering the Threshold


Deep Sky Observing with 70 , 80 and 100mm Binocs

Tonight's objects with 25 x 100 IF Oberwerks

Rain Delayed Observing


An Explanation of Contrast Ratio by Bill Ferris



Surface Brightness (Sb)

Visual magnitude of a deep sky "extended" object is almost always NOT the appropriate measure of how faint the object will appear. Observing faint extended objects such as galaxies is complicated by the fact that books generally list the visual magnitude, but a better indicator of whether or not the object might be seen is Surface Brightness (Sb), and even that can vary due to being brighter towards the middle and fainter towards the edges.

For an object like M101 that has a visual magnitude of mag 7.7, but an area of diameter 26 arcminutes, that light is spread out over 530 square arcminutes. Hence is has a very low Sb = 14.7. That is averaged. As you get out towards the extremities of the object, it is fainter, in towards the center it is generally brighter. So for instance a galaxy with a bright core might be visible, but it would appear much smaller than its full size because you can see the core but not the extension.

M101 has some brightening towards the core, so the core area actually has a little brighter Sb than 14.7, while the extremities are fainter than the average Sb of 14.7. Another example is M33 in Tri, at Sb 14.0 it's fairly easy. This one also has a broad brighter core, so in these cases we generally see just the brighter core area and it's generally brighter than the average Sb that's listed.


******************************************
Occasionally, someone comes along and asks, "Why can't I see this galaxy, the book says it is mag 9, that should be easy enough?" The answer lies in the definition of Surface Brightness. Surface brightness will be referred to as Sb.

The criteria we use to determine the limiting magnitude (faintest stars seen) of an instrument do not always give a good indication how well an instrument will perform on all types of objects, especially faint entended objects. These have an entirely different set of requirements. Total light gathering (aperture) is important, but, to differentiate a very low surface brightness object from the background sky takes good contrast. Lower surface brightness objects have very little contrast with the background sky, hence can be very difficult to see.

The magnitude scale works like this. A difference of 5 magnitudes (from mag1 to mag6) is a difference of 100x light, brighter or fainter. Therefore, each magnitude is 100 to the 5 root from the next. That is, one magnitude is approx 2.51x brighter or fainter. So 1 mag difference is 2.51x, a 2 mag difference is 2.51 x 2.51, and so on.

For extended objects, (any object that produces an image larger than the Airy disk of the aperture), the visual magnitude Mv, is given as the magnitude the object would appear if all of the light from the object could be condensed into an area 1 square arcminute. Almost all extended objects have a size much larger than that. For the purposes of figuring Sb, each increase in area of the object by 100 to the 5th root (or 2.51x) will result in a decrease in the apparent brightness of the object by 1 magnitude.

Let's use an example of a DSO listed as visual mag 9. If the object size is 2.5'x2.5' then it has an area of 6.25 sq arcmin. The light would be spread over an area 6.25x greater than the compressed area used to determine the Mv value. It would actually appear 2.5x2.5, or 6.25x fainter than the visual magnitude. From above, we know a light difference of 6.25x is equal to 2 magnitudes, so the Sb of this object would be Sb = 9 + 2 = Sb mag 11.0. BUT what if the object size is 10'x10', then it has an area of 100 sq arcmin. The light would be spread over an area 100x greater than the compressed area used to determine the visual magnitude measurement. It would actually appear 100x fainter than the visual magnitude. A light difference of 100x is equal to 5 magnitudes, so the Sb of this object would be Sb = 9 + 5 = Sb mag 14.0.


The second concept that must be considered is brightness gradients. Look at the photos of almost any galaxy or globular cluster. Often the central core is much brighter than the outer fringes. Our 10x10 example object might appear with the central 50 sq arcmin at Sb 13.0 and the outer edges 50 sq arcmin at Sb 15.0, for an "average" of Sb 14.0. What we would see is the brighter central area. We may not see the outer fringes at all.

Some example galaxies as observed in 25x100:

Using 25x100 binoculars, I have observed several faint extended galaxies that have little to no brightening of the core (meaning the core was not significantly brighter than the spiral extensions). Many of the faintest Surface Brightness galaxies are face-on. Under mag 5.4-5.7 skies, in approximate order of difficulty, some I was able to see were:

M 33 in Tri has a visual magnitude (Mv) of mag 5.7 but it has Sb = 14.0. Its size is a very large 62'x39'. The area of this galaxy makes its Sb about 9x fainter than its Mv value. But it's actually fairly easy to see! Why? because it has a broad brighter core and wispy faint extensions, so we only see the brighter core.

NGC 3628 in Leo near M65/M66, at Sb 13.5 was pretty easy, more edge-on than face-on, it measures 4'x15' and has a bright core.

M 95 in Leo is 7'x5' and has Mv about 9.6. About fout magnitude fainter its Sb 13.6 was not as easy, but a small 3' core is brighter, so makes the center easier to see..

M 101 in UMa is Mv 7.7, but has Sb 14.6 and it is not very easy. Its size is 27'x26', but it shows only about 15' dia. with a slight brightening to the core. This means the 15 arcmin diam. that we see is brighter and the outer fringes are much fainter than Sb 14.6.

M 74 in Psc at Sb 14.4 is difficult, weakly brighter center, size is 10'x10', so visual magnitude is Mv=9.0, but this is no indication of how difficult this is to see.

NGC 6946 in Cyg (near Cepheus) has Mv 8.9, but it's size 11'x10', and the fact it has no brighter core at all makes it a very even lit and difficult to see Sb 13.8.

IC 342 in Cam at Sb 15.0, with little brightening in the core, broad face-on wispy galaxy, difficult even in the best conditions. It's 18'x17' means it's Mv is labeled about 6.25m brighter than its Sb. Whereas Sb=15.0, Mv = 8.75.


For me, IC342 has been one of the most difficult galaxies in all the sky for my small instruments. It has a surface brightness of mag 15.0. As a comparison M74 has a surface brightness of mag 14.4. NGC 2403 has a surface brightness of 13.9, about the same as M33, easier than M74 and much easier than IC 342.

What can you roughly predict from this. In NELM mag 5.4 skies, with 100mm objectives I can gather enough light that I can see faint extended objects with surface brightness 8.0 to 9.0 magnitudes fainter than NELM. Using this instrument under this sky I gather enough light to get enough contrast to see about 9.0 mag fainter than sky. That is the limit of contrast detection I can get.

Either a smaller aperture or a brighter sky may not allow that limit. So, as far as NELM goes, if mine were let's say 4.9, a half magnitude brighter, it would be likely I would lose sight of probably all but NGC 3628.


So, What happens to faint Low Surface Brightness Objects as we vary aperture and magnification?

OK, let's try increasing magnification to darken sky background and increase contrast. This works great on stars since it doesn't decrease the brightness of the stars but it does decrease the brightness of the background sky, which is an extended object, so you get to see fainter stars. However, with an extended object such as a faint face-on galaxy, the problem you will have with trying to darken a bright background sky by increasing magnification is that you have a very narrow range where that will produce a darker sky and yet still provide a large enough exit pupil or enough brightness to the eye to keep the image bright enough for the eye to see the very faint object.

If you increase magnification in hopes of darkening the sky background, you reduce exit pupil and you will also darken the extended light of the galaxy. If you increase the aperture too much without increasing magnification, you increase exit pupil and you will brighten the entire image, both object and sky background, and you may get a washed out image. However if you increase aperture AND increase magnification, maintaining constant exit pupil, you may improve the contrast detection of the faint extended object because you have gathered more light. Of course this will only work when sky is dark enough to permit at least reaching the lower magnitude limit of contrast detection.

So then, 'under brighter local light pollution, magnification increases in importance relative to aperture' would always be true for viewing stellar targets and is usually true also for very bright extended objects but is may not help at all for very faint, extended, low surface brightness objects.

On the other hand 'under darker skies, there is more gain from increasing aperture relative to magnification' is probably always true, at least up to the limit of the eye pupil. Exceptions to this would be very small extended objects that require increased magnification to increase image scale or to reach ODM, optimum detection magnification. (see Binoc Web Links - Mel Bartels).

How are you supposed to know what works? I guess the answer to that is go out and observe as many objects as you can in all kinds of conditions with as many different instruments as you can get your hands on. You'll find out what works.

edz






Edited by EdZ (06/05/10 08:28 AM)


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Binoviewer - Scope - Binocular Equivalents new [Re: EdZ]
      #1384879 - 01/26/07 01:46 PM

It is necessary to understand all of this information to get a clear picture of the equivalents from binoculars compared to scopes and finally compared to scopes with binoviewers.

This thread gives data collected from three different models binoviewers and shows how clear aperture restricts field of view. A summary is given for lowest power acceptable field of view for binoviewers and then it is also given as a binocular equivalent. The comparison is made to show lowest power widest field of view available in stock bargain binoviewers as compared to binoculars primarily in the range 70mm to 100mm.
Binoviewers and Binoculars (equivalents)


See also the Best Of thread on Binocular Summation, the benefit of two eyes.
Binocular Vision Summation - Two Eyes vs One Eye

Binoviewers and Clear Aperture
If selecting one of the 20mm CA binoviewers on the market, not only is there a light loss at the outer edges of the field stops, but also the Maximum True Field of View that you can get will be restricted to eyepieces with field stops about 22-23mm max. You can purchase a more expensive binoviewer with a 26mm or more clear aperture to get wider BV field of view.

Is there a scope that's best for binoviewing?
This post I put in the Binoviewer forum starts out " A few things you should know about binoviewers and scopes". I notice people in discussions about their binoviewer equipment have a few misconceptions. What I try to do in this post is explain not only how clear aperture affects the field of view, but also how the various attachments to the binoviewer nose change from the specified magnification factor when used in different scope/diagonal configurations. It is my experience, some people that are using binoviewers with an SCT scope have not attempted to determine what magnification they are using or what they are getting for true field of view. It is not as simple as assuming all the stated nominal factors and focal lenghts control. This post helps explain some of the above.



edz

Edited by square_peg (10/07/09 11:44 PM)


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First Binocular Purchase? Questions? new [Re: EdZ]
      #1384880 - 01/26/07 01:47 PM

What do you recommend for a first binocular? What can I expect to see?

This is not an uncommon question at all, but one that usually should at least stir up another 10 questions. Before anyone can make any recommendations to you, YOU need to answer a lot more questions about yourself and your needs. For instance, What do you intend to See with this binocular? When you have developed some thoughts on each of these questions, and you begin to understand some of these basic things about binoculars, then we can reasonably recommend a binocular that will work for you.

Here’s some of what we don't know about you that would be helpful for making a recommendation:

Do you wear eyeglasses?
If so, will you always wear them when using the binocular? For eyeglasses, consider a binocular with about 14-16mm eye relief. 11-12mm is tight and you will lose some of the field of view. 8-10mm of eyerelief is extremely tight and if you have eyeglasses on, your eyes will be so far behind the proper eye relief point that you will not be able to see a large portion of the field of view.

Do you know your Inter-pupilary distance (IPD)?
Some binoculars are not made to fit people with narrow set eyes. If you have eye pupils that are set only 56mm apart, a binocular that has a minimum of 58mm is no good for you. The Swift Ultralite 8x42 gets down to 51mm, but the Orion Vista 8x42 only closes to 59mm. All the Nikon Action Extremes get down to 55mm. But some of the larger 20x80 and 25x100 binoculars have a smallest (closest) setting of only 60mm. Most children cannot use binoculars that don’t get down to 56-58mm.

Do you know how large your eye pupils are?
Under dark conditions, if your eye pupils open to 7mm, you would be able to use the full exit pupil from most all binoculars. BUT, if your eye pupils don't get any larger than 4mm or 5mm, it won't do you any good to carry around the extra weight of the glass needed to provide a very large exit pupil. 12x60, 10x50 and 8x40 are all examples of 5mm exit pupil binoculars. 20x80 has a 4mm exit pupil. 10x60 has a 6mm exit pupil. 10x70 has a 7mm exit pupil. 7x50 has a 7.1mm exit pupil. If you have maximum 5mm eye pupils and you use a 10x70 binocular that has a 7mm exit pupil, your smaller eye cuts the effective aperture to 50mm and eliminates all the light outside that. You can pretty easily have someone help you measure your eye pupils in a fairly dark room. An easy method is to use a strip of paper with a series of dot sizes, sliced thru the middle of all the dots.

Will you observe in very low light conditions?
A 10x50 has only a 5mm exit pupil, but an 10x70 has a 7mm exit pupil providing a far brighter image, and that would be useful IF your eye pupils open wide enough to take in all the light. Generally, binoculars with such large exit pupils are used by people who can view from very dark skies. Or for example for terrestrial observing the choice might be between a 8x42 or a 8x56. The 8x56 would give brighter images and be more useful under low-light conditions. Actually, I consider binoculars with 7mm exit pupils as specialty binoculars and I would rarely recommend them to a first time buyer. Pay attention to eye pupils here again. As far as light goes, you can only use an exit pupil as large as your eye pupil.

Do you demand a waterproof binocular, or simply a weatherproof binocular?
There are waterproof binoculars, water resistant binoculars and binoculars that have no resistance to water infiltration. If you plan often to use your binoculars down by the seaside, you will most certainly want the ability to wash off the salt spray. For that you need waterproof. For astronomy it may not be needed at all. However, it will keep moisture from ever fogging up the insides, and that’s a good thing.

Have you any experience hand-holding binoculars?
You need to give some consideration to how much weight you can hold for long periods or how much magnification you can hold for a steady view? My 7x35 Minolta Activa weigh only 24oz. The Swift Ultralite 8x42 weighs about 22 ounces. The Nikon Action Extreme 10x50 weighs in at 36 ounces. The Oberwerk Mariner 10x60 and the William Optic ED 7x50 each weigh over 48oz. Generally holding anything over 10x is not an issue with the weight as much as it is an issue holding 10x power steady enough to stop the image from swimming around in your view. Some 15x70 binoculars weigh only a little more than 3.5#, but at 15x, every little movement of your hands or arms or even your heartbeat, will show up in the magnified image. I’ve handheld my 4#12oz Fujinon 16x70 for brief periods, but I wouldn’t want to use them handheld for a full night. Some recommend the consideration of IS binoculars.

Have you any experience with wide-field versus narrow-field?
Things in motion put more demands on how much field of view you use. 15x70 binoculars usually have a little more than 4.0° field of view. The Nikon SE 12x50 has 5°. Many 10x50 binoculars have about a 6.0° field of view. The Nikon Action Extreme 8x40 has an 8.0° field of view. A 25x100 or 20x80 binocular will generally provide only 2.5° to 3.0°. If you don't know the differences between what the fields of view (fov) look like, then you need to try about three different sized pair with different fov. Put one edge of your view on the exact same spot for each binocular and make a note of how far across a wall it can see. Compare with the others. Every 1° field of view is 1.75 feet across at a distance of 100 feet. You need a 5-6° field of view to fit the Hyades. You need only 3° to fit the Pleiades with room to spare.

Here’s some of what people will talk about that you should know at least a little bit about:

What difference do multi coatings make?
Coatings are a very important product in the transmission of light. In this age of products, no one should purchase binoculars that have uncoated surfaces. An uncoated lens surface can reflect 4% of the light hitting it. Uncoated internal surfaces contibute to more internal reflections and lowered contrast. Magnesium Flouride (MgF) single coating can reduce reflected light to 1.5%. Properly applied multicoatings can reduce that reflectance to 0.5% or 0.25% per lens surface. A binocular may have as many as 14 lens surfaces. With the exception of extremely high level of performace of some superior coatings, even a properly muticoated binocular can transmit at best only about 93% to 96% of incoming light. The same binocular with all 14 surfaces only single coated with MgF may transmit only 79% of the light. Subtract a few tenths of a magnitude from the “how faint” numbers above for any binoculars that are not fully multi-coated.

What’s Chromatic Aberration?
Binoculars can suffer from a number of aberrations but this one is often discussed. Chromatic Aberration (CA) is the result of the various wavelengths of light not reaching focus at the same precise point in the image. CA is a function of refraction. Light from different wavelengths is refracted differently. Blue, yellow and red wavelengths of light reach focus at slightly different points along the focal length axis of the lens. The most important thing the user should understand is that it is impossible to completely eliminate CA from a lens system. It can be reduced, but cannot be eliminated altogether. In an astro binocular, it appears prominently in less than 1% of the objects viewed. So it should be one of the least critical aberrations on which to base a decision, unless of course you are buying your binoculars just to look at the moon. Judge your choice of binocular on all the features that make a difference in the view 99% of the time. Honestly, the planets are not binocular targets, so the moon is the only astro target that would be a consideration for judging whether one needs to consider CA in the choices of astro binocular. For terrestrial viewing, CA becomes an important factor. CA becomes a problem in extremely bright conditions, not in low light conditions.

What’s all this talk about sharp field of view?
Sharpness of field image is deteriorated in the outer field of view by a combination of other aberrations, the scope of which is beyond this discussion, but they are coma, spherical aberration, curvature and astigmatism. Generally (but not always), a wider Afov binocular will suffer from more aberrations in the outer portions of the field of view. Much of those aberrations are contributed by the eyepieces, and it takes a very high quality eyepiece to successfully eliminate the aberrations in a wide field. Think about the cost of the binoculars you have in mind, and then think about the cost of a pair of good 18mm to 22mm widefield eyepieces. Usually, binoculars don’t have the highest quality eyepieces. Therefore, somewhat narrower Afov binoculars, usually in the range of afov 60° and lower, have less aberrations in the outer field of view. Many Pentax binoculars use very narrow Afov eyepieces, resulting in a narrow but extremely well corrected and sharp field of view. It doesn’t do you much good to purchase a wide-field 20x80 with an Afov of 70° if the outer 30% is degraded. You may as well get a 20x80 with a 60° Afov with less aberrations.

Why do these binoculars look the same, but one is so much cheaper?
Probably the most important differences in any two binoculars that look the same but sell for much different prices is (A)the mechanical construction, workings and range of adjustment, and (B)(and very likely more important) the degree to which all the optical surfaces have been figured, polished and coated. There are other things that make a difference in the quality and most of them are not visible on the outside. Usually, cheaper is not just cheaper for no reason at all.

What should I consider for a mount?
Many times people ask, Why do you always say you can't mount an 8# binocular on a tripod that is rated for 8#. That is because the load rating for tripods is determined with the load weight directly over the tripod head and directly over the tripod column. Furthermore, load ratings are based on cameras with little to no magnification. With binocular viewing, we often have a heavy load hanging off of one side. That is like a cantilever or an eccentric load. In all things mechanical, it takes a beefier support to hold an eccentric load than it does to take a direct load. Add to that some 10x or 12x or 25x magnification and you can see the need for stability goes up exponentially. If the tripod is tall enough, you can mount a 2# to 4# binocular on most tripods from $90 to about $150. BUT people are often surprised to find out once they have spent $300 to $400 on an 8# 20x80 or 10# 25x100 binocular that they now must spend $350 to $500 on a substantial tripod and fluid head to hold such a large instrument.

Here's some idea about what you might be able to see with some different sizes of binoculars:

How faint are the stars you can see with binoculars?
First judge how dark are your skies naked eye. If you can only see 6 of the stars in the Little Dipper, then you have no better than mag 4.5 skies. If you have skies that allow you to see all seven main stars in the Little Dipper naked Eye, then you have mag 5.0 skies. If you are able to see 9 or 10 stars in the Pleiades naked eye, then you have mag 5.5 skies. That’s pretty decent. Under mag 5.5 skies you can see stars just fainter than mag 10 with a 10x50, stars to mag 10.5 with a 12x50, stars to mag 11 with a 15x70, stars to mag 11.5 with a 20x80 and stars to mag 12 with 25x100. It is very difficult even with the best 70mm binoculars to see stars beyond mag 10 when handheld. Seeing stars at mag 10 requires a completely quieted binocular on a stable mount, viewing without touching the eyepieces. For mag 4.5 skies subtract a full magnitude. For handheld binoculars subtract another full magnitude or even more.

What can some various sizes binoculars see?
Keep in mind, you will not see as much handheld as you will with mounted binoculars. Assuming at least mag 5.5 skies:

In an 8x40, many of the smaller open clusters or fainter globular clusters and nebula such as M76, M26, M9, M10, M14, M71, M18, M1 and M78 are barely seen as a smudge or cannot be seen at all. 8x is a bit low for astronomy and it could be seen readily when compared to 12x or 15x on clusters. However 8x did perform very well on some objects. I easily found M13, M27, M29, M11, M35, M36, M37 and many other open clusters, but M11 was barely a smudge. On M36 you will see the glow of the cluster, but no stars will be resolved. M38, M46 and M67 might be missed. Doubles 20” can be split, but none smaller. Even the smallest binoculars will see the 4 moons of Jupiter and can see bright Titan, although you would have difficulty even telling that Saturn is elongated.

10x50 binoculars can see many open clusters and in a good dark sky will find a large number of the brighter galaxies and nebula. Both M81 and M82 can be seen handheld in a 10x50, but M51 needs a mount. A few bright globular clusters can be seen, but they will be small, however they will appear distinctly non-stellar. M5 can be seen handheld, M10 is seen but very small and M12 was just barely seen. In the Nikon AE 10x50 held braced, I saw M15 as a small but obvious globular. Doubles can be resolved down to about 16 arcseconds. M11 is still just a faint patch. You will be able to see the Ring nebula, but only just barely be able to see that it is a non-stellar spot. The broad galaxy M33 can be seen, but a similarly broad galaxy M101 will not be seen as it is too faint for 10x50 in mag 5.5 skies. Using a 10x60, M78 was just barely detected. The beauty of binoculars like 10x50 with a 6° fov is that objects like the Hyades can be seen all in one view.


12x50 binoculars will capture nice views of M42, M45, M11, M27, M71, Alberio, Sagitta, Delphinus, CR399, and the Cygnus Milky Way. Bright globular clusters can be seen, but they will still be small, however more will begin to appear as obvious globular clusters. Doubles can be resolved down to about 13 arcseconds. You will be able to see the Ring nebula distinctly as a non-stellar spot. 12x50 is still not enough to see M101 in mag 5.5 skies, but M1 easily and M78 just barely were detected handheld using a Nikon SE 12x50.

In 15x70s and 16x70s, objects like the galaxies M65 /M66 can be seen. However M65 is difficult in a 15x70 and just a bit easier in the Fujinon 16x70. The companion NGC 3628 is not be seen in either. Portions of the North America nebula are visible. You can split doubles down to 12", and sometimes 10" with difficulty. M11 takes on the appearance of a glow with a faint star. On the steadiest nights, although you might suspect resolution of all four components in the Trapezium, most people can only positively see three components. On M36, a 15x70 can separate only 4 to 6 stars, while Fuji 16x70 saw about 8 stars resolved. When small and faint M78 was seen with difficulty in a fine handheld 12x50, it was found quickly and easily in the 16x70. M101 can be seen under the best conditions, mag 5.5+ and excellent transparency. Saturn can be seen with a little black space between the rings and the disk.

20x80s are solidly into the range of giant binoculars. Image scale grows. The field of view narrows to about 3°. You see more stars in clusters just due to the increase in magnification. In clusters like M44 the Beehive, an 8x40 will see only about 40 stars, in a 10x50 you might see 50 stars, in a 15x70 maybe 80 stars, but in a 20x80 over 100 stars. On M36, a 20x80 can resolve about 6-8 stars. You can sometimes pick out all four stars in the Trapezium, the closest being 8.7". You can see magnitude as deep as 11.2 to 11.5 and occasionally elongate some not-so-bright equal doubles in the 7" range. Some of the fainter galaxies such as M95 and M101 can be seen on good nights. On a night of mag 5.0 skies, M76, the Little Dumbell nebula in Perseus was not seen in a 16x70 but in a 20x80 it was very faint and obviously not star-like.

In a 25x100 binocular the field narrows to 2.4°. These binocular see stars at mag 12.0. When you view faint clusters in these binoculars you see stars that just were not there in any smaller binocular. On M36, a 25x100 can see about 20 stars. In M44 I’ve counted over 150 stars in a 25x100. Doubles of 7" are clearly separated. M105 and its companion NGC 3384 make a nice pair. M57 is an obvious torus. M81 and M82 were both very easy and bright and both show extension beyond a much brighter core. Fainter galaxies seem to be easy pickings for these 100mm binoculars. While M66 is seen bright, and M65 is difficult in 16x70s, both are readily seen in the 25x100s. In addition, the companion NGC 3628, not seen in any smaller binocular, was visible several times in the 25x100. 25x100s make globular cluster M12 look like it is on the verge of resolution in the outer edges. 16x70s could see but could not resolve M12 at all.

Now then, coming around to what might help you make your decision:

So what is your goal?
Do you want to scan around and see the sky in general? Do you still need to learn your way around the constellations? If so, get a low power wide field binocular. You might be content with an 8x40, but I’d go for a 10x50.

Do you want to observe mostly open clusters and some of the brighter deep sky objects? Maybe you have no desire to lug around a 8#-10# binocular mounted on a 10# tripod, and sometimes you might prefer to just ahndhold your binocular for a few minutes. A low to moderate power and light weight 12x50 up to a 15x70 is a great choice for this.

Do you want to see both large and small clusters, hunt down faint objects and see extension in galaxies? A 15x70 might do it for you. But if you want the most out of deep sky viewing and you will consider investing in a good mount, then you should be looking for a 20x80 or 25x100 size.

If you're looking for a handheld binocular, then consider this; If you don't like the way a binocular feels in your hands, it probably isn't a good choice for you no matter what the specs indicate. One of the primary advantages of binoculars over telescopes is comfort and ease of use. No matter how outstanding a binocular is optically, if it isn't comfortable for YOU, it's probably not a good choice. If your looking for a large mounted binocular, you must consider whether you currently have enough of a mount or will you invest in a proper mount.

Don't rush into accepting recommendations because someone thinks this or that is great. Consider all the information provided to you, but get a binocular that fits you like a good pair of shoes. When you wear them, they get the job done right, and you can't even tell they are there.

These models mentioned here are not necessarily recommended choices, but in the context of getting to the questions that need answers, they help make the point.


Some other threads that will be helpful in your quest
I would also suggest all beginners read these two threads
Testing Binoculars in the Store Before Buying

and

These Look The Same, are they?
This post summarizes a lot of the quality differences that might exist among various brands and price levels of binoculars, most of which would never be evident by looking at the outside of the binocular. With this post we try to do our best to provide you the information you need to dispense with the often heard internet myth that they are all the same. It's just not so.

See more on this subject thru this Best Of link
If They Look the Same, What Could be Different?


Read about Exit Pupil vs Eye Pupil here
Affect of Eye Pupil on Binocular Aperture THREAD

Affect of Eye Pupil on Binocular Aperture CN REPORT

What makes a particular binocular good for astronomy?





edz


Edited by EdZ (12/15/10 02:48 PM)


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EdZ
Professor EdZ
*****

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
GOOD STUFF FOR BEGINNERS new [Re: EdZ]
      #1384884 - 01/26/07 01:48 PM

Welcome. Some posts have been assembled here that will help the beginner get going on the right path. For the most part, this post is no different than every other post here in the Best Of thread. It provides you with links to all the relevant information on this specific topic. As you progress in your quest for knowledge, you can go to each of the specific topics in this Best Of section and read much more related to each specific topic.

Thanks to Steve Napier for suggesting this topic.

Thanks also to Stephen Saber for getting us started with this post.
Beginners and First Time Buyers Start Here for links to offsite sources with lists of definitions

I can't tell you how often someone comes new into this forum and asks, "What do you recommend for an all-around astro/terrestrial binocular?" It is our collective experience here that there are questions you need to ask yourself before people can make good recommendations for you. This list of questions has evolved into a brief article that will help the "first time" buyer answer some questions about themselves, their needs and their goals and will help them understand what can be expected from some various sizes of binoculars. See the "Best Of" post here titled
First Binocular Purchase? things to consider
for some ideas about things you should consider and what you might expect to see.


This offsite link takes you to a very well written and illustrated article
Binoculars - A Basic Guide for Astronomy
by Dennis Simmons

I would also suggest all beginners read these two threads
Testing Binoculars in the Store Before Buying

and

These Look The Same, are they?
This post summarizes a lot of the quality differences that might exist among various brands and price levels of binoculars, most of which would never be evident by looking at the outside of the binocular. With this post we try to do our best to provide you the information you need to dispense with the often heard internet myth that they are all the same. It's just not so.

See more on this subject thru this Best Of link
If They Look the Same, What Could be Different?


One question that a beginner often asks about is exit pupils. There is so much talk about exit pupils that it can be thoroughly mind-boggling. This primer will set you on the right path. When you begin to yearn for more information visit the Best Of links dedicated to Exit Pupil and Affect of Exit Pupil on Binocular Aperture.
Binocular Primer - An explanation of Exit Pupil, Eye relief and Field of View


Exit Pupils 5mm vs. 7mm, or Should I get a 7x50 or a 10x50?
this will help explain why a large 7mm exit pupil is good only in certain conditions.

What are the Issues with Handheld Binoculars?
Handheld Binocular Observing Issues
not only weight, but magnification is a major issue


Advertised Eye Relief versus Effective Eye Relief
the depth of the recess to the lens affects how much eye relief you really get to use. Usable eye relief is often a lot less than advertised.

Sometimes eyerelief is a little too long, especially for eyeglass wearers when the eyecups are folded down. This may cause blackouts. There are some simple fixes; Here's one shown with pictures.
Solution to the Nikon 10x42 SE blackout problem


The best place we can direct you to understand more about the importance of COATINGS is the Best Of thread dedicated to the topic of coatings. There is a very good summary right in that single post that should help you understand the importance of coatings. If you wish, there are links in that post that will take you into more involved discussion.
See all about Coatings here




Looking for a good book to get started?
This discussion will help you sort out which guidebook would be most helpful for you
single best book for a binocular astronomy beginner
there probably isn't just one best book, but this thread will help you by asking what are your needs and will highlight a few books depending on what they are, learning the sky, deep sky, science, technical aspects or repair.

Binocular observing books? this thread is a goldmine of contibutions by many members of the forum. Books and Charts for observing.




Here is a post that has some good recommendations of binoculars for a first time buyer. Of course this assumes you've at least visited several of the links above here and read the primers and have answered some questions for yourself. In this link you will find a well organized presentation of suggested binoculars put together by Mike Swaim. While originally prepared for the purpose of recommending to beginners various binoculars for specified use or price ranges, Mike's gathering and organization of information leads us to a collection of short mini-reviews within product lines. Mike touches on over 30 different binoculars in this very worth-while post that groups binoculars by power and by price ranges. Along the way, he explains a few simple things the beginner needs to know when shopping for a good first binocular.
Light Trap's beginning binocular suggestions


TAKE A POLL
Binocular Forum Polls Page
take about 30 seconds each or less to answer and see what everybody else says


Small binoculars spreadsheet
manufacturer specifications in the spreadsheet for about 20-30 binoculars

edz

Edited by square_peg (10/07/09 11:39 PM)


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EdZ
Professor EdZ
*****

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
Binocular Telescopes new [Re: EdZ]
      #5236768 - 05/24/12 06:39 AM

--Binocular Telescope Beginnings

The basic concept of a “binocular telescope” goes back in history to around 1608 when Hans Lippershey, a maker of eyeglasses, combined two small telescopes of his own original design into a binocular configuration. It wasn’t until the 19th century, though, that the aperture of these instruments and prismatic design approached what we now associate with large astronomical binoculars.

While larger aperture binoculars are relatively new to the modern amateur astronomy scene, there have been a number of “giant” or “big eye” binoculars developed for use by military forces over the years for battle front and naval applications. These giant binoculars used large aperture objectives from 80mm to 250mm at magnifications from around 10x to as high as 50x. Because of limited available light and/or the rolling motion on deck, these binoculars featured large exit pupils that made it easier to locate targets under adverse conditions and keep them in view once located. Many of these binoculars also featured angled eyepieces to make sweeping the skies for aircraft more comfortable.

Over the years, a few of these giant binoculars remained in production for civilian use; it was only logical that someone would turn them up to the sky and realize that they gave wonderful views of the heavens as well. Probably the most well known of these today are the Fujinon 25x and 40x150 giant binoculars. Available in straight-through as well as angled designs over the years, these single magnification binoculars have become the gold standard of giant binoculars used for astronomy.

In the 1990s, a Japanese optical company called Miyauchi developed large, lightweight binoculars specifically for astronomical viewing. They featured both 45° and 90° viewing angle models to alleviate the neck strain caused by looking up at high angles with straight-through designs. These angled binoculars were made as small as 60mm and as large as 141mm. All provided the non-reversed, correct view that we have come to expect from binoculars. What really set these Miyauchis apart from the crowd was their provision of several interchangeable proprietary eyepiece pairs rather than fixed eyepieces so that users could change magnifications with these binoculars just like they were already accustomed to doing with their telescopes. Vixen Optics of Japan also brought out their BT80 and BT125 45° binoculars, first with fixed eyepieces and later using interchangeable 1-1/4” eyepieces. By definition, at least in our circle here at Cloudy Nights, this binocular form has become known as a Binocular Telescope (BT). While not intended for high magnification use, BTs can be used comfortably up to around 75x and can give astounding views of Milky Way starfields, dark nebula as well as many DSOs.

While Miyauchi may have developed the modern Binocular Telescope, they never had a large market due to high costs and limited production runs. Their mechanical and optical quality was held quite high but because of that they were never able to break into the mass optical market that has become increasingly more cost conscious. Sadly, of late, Miyauchi no longer produces BTs. Vixen still makes their 80mm and 125mm BTs. The Japanese firm Kowa, of camera and spotting scope fame, makes an ultra- premium BT of similar design to the Miyauchi but suffers similarly with proprietary eyepieces and even higher cost. It’s a great performer if you can afford it.

In the last decade, larger Chinese manufacturers copied the Miyauchi design and, while having to make some compromises to save cost, have hammered out most of their early problems and now produce a pretty solid product. As a plus, they have adapted the design to accept standard 1-1/4” eyepieces which has made it easier to appeal to every viewer’s personal needs. These Miyauchi “clone” BTs are now available from dealers such as Garrett, Telescope Service and APM in apertures ranging from 70mm to 150mm. A 100mm BT of this type is a relatively lightweight 13-15 lbs and mounts easily on a sturdy photo tripod and video head.

Not to be omitted here, another popular BT offering the same abilities but of a slightly different, heavier but likely more robust “unibody” design is based on Chinese military border binoculars. This design has now evolved into the Oberwerk BT100/45°. It’s about twice the weight of the competition so needs a sturdier tripod and head to support it. Many CNers use this BT and are quite happy with its performance.

Expect a maximum 2.5° FOV at around 25x in the 100mm versions of any of these BTs.

--What Is The Advantage of a Binocular Telescope ?

Any binocular, due to the summation of two eyes instead of one, will give you a view with greater brightness and contrast than a single objective/eye. There are a number of informative posts in the Binoculars “Best Of” section on the particulars of binocular summation. Comparing a binocular telescope view to that of a telescope/binoviewer combo, the BT will be equivalent to a telescope of 1.4x greater aperture. This means that a 100mm BT will deliver the same amount of light to each eye as a 140mm scope/BV combo.

You may ask “why should I get a binocular telescope when I can just put a binoviewer on my telescope?” The simple answer is this; a binocular telescope using two 100mm objectives will have a shorter focal length than an equivalent 140mm refractor used with a binoviewer. Since most BVs are in the 1-1/4” format, you cannot use wide field 2” eyepieces to make up for this longer focal length. The shorter focal length of the BT obviously results in a lower magnification, wider field view than with the scope/BV combo. For wide field Milky Way sweeping it’s hard to beat the binocular telescope. The two-eyed wide field vistas we see are oriented in the sky exactly as we see them naked eye or on our charts; it’s as if suddenly you are thrust deep into space where you are immersed in the area you are studying. Using two eyes stimulates both hemispheres of your brain and you can’t help thinking you are there among the stars! You can sit comfortably in a chair and the angled, interchangeable eyepieces of a BT allow you to view at high angles with a simple, light mount that needn’t weigh any more than the BT alone.

Try looking through a binocular telescope if you have the opportunity; I think you will be pleasantly surprised by what you see!

Rich Vadenais


Vondragonnoggin's mega thread - 12/03/10

Garrett BT70-90 MK II's arrived!

curiosdad's thread discussing 45 vs. 90 degree models - 5/16/12

Convenience, 45 ° or 90 °?

Mr. Bill's recent DIY project - 6/8/12

127mm f/5.5 binocular

Edited by Zdee (07/30/12 01:48 PM)


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