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Equipment Discussions >> Binoculars

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Professor EdZ

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
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

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.


Edited by square_peg (10/08/09 12:23 AM)

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Professor EdZ

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
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


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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Professor EdZ

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
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.


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.


Edited by EdZ (06/05/10 08:28 AM)

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Professor EdZ

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
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.


Edited by square_peg (10/07/09 11:44 PM)

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Professor EdZ

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
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


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?


Edited by EdZ (12/15/10 02:48 PM)

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Professor EdZ

Reged: 02/15/02

Loc: Cumberland, R I , USA42N71.4W
      #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


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

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


Edited by square_peg (10/07/09 11:39 PM)

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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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