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nemo
sage
Reged: 06/09/03
Posts: 388
Loc: Eugene,Oregon
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Friends,
I was thinking about contrast versus resolution the other day and realized that my understanding as to what
Constitutes each as well as the possible differences and similarities between the two is more than a little fuzzy:) I guess this is one of those compare, contrast and define questions. I know that signal to noise ratio comes in here but as I say my comprehension is not that good. I always thought that I knew the difference but as I examined the two concepts I realizes that I do not. Would there be some one out there who could enlighten me? I know that an object could easily be very contrasty and still not be clear or well resolved but that is as far as I get. Can something be in good resolution but have very poor contrast?
R/S,
Dan
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"Humility is not thinking less of your self-it is about thinking of yourself less."
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KennyJ
Reged: 04/27/03
Posts: 10163
Loc: Lancashire UK
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Dan,
Your question is a most valid and interesting one that I hope attracts a few responses from the "technical heirarchy" in our midst ( self most definitely EXCLUDED :-)
Our "resident guru" Ed Zarenski touches upon the subject in his admirable "Best Of" section , but I know he has a far deeper understanding of the relationship between contrast and resolution than might be assumed by the casual reader of THAT particular reference.
I would also add that there is in my opinion a difference between the application , utilisation and significance of these definitions and their relationship as applied to ASTRONOMY when compared with TERRESTRIAL viewing , due entirely to the differences in natural light in which the objects are being viewed and the differences in the nature of the physics of light with regard to objects seen in the night sky and objects seen on planet earth in daylight.
It is a very complicated subject -- even without the added complication of the complexities of the human eye and differences from individual to individual in visual acuity, and even how the acuity of an individual person can alter quite dramatically over the course of time.
The "article" I promised a month ago as " might appear soon on the "freeview" section of CN articles" unfortunately got lost in cyberspace and has just been re -posted in it's complex entirety following an almost equally complex one hour exchange of communications with our webmaster.
This article , whilst not specifically addressing your question , might go some way to clarifying certain apsects surrounding the topic , if and when it eventually appears for communal perusal.
As far as your initial question is concerned Dan , to summarise , I believe it IS possible for an image to have
good contrast per se , without necessarily having good resolution, but not vice -versa.
I could expand upon this assertion quite a lot ,but would hate to give the impression that it was ME who deserved any credit for the explanation.
I look forward to seeing responses to this question from members better qualified to answer it.
Regards -- Kenny.
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If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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lighttrap
Reged: 02/06/04
Posts: 3833
Loc: cloudy, foggy, humid NC, US
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Here's my fuzzy-headed 1st reaction to this topic:
Because resolution is wavelength dependent, I'm not sure that it's particularly practical to try too terribly hard to explore the differences between contrast and resolution. Usually, those two functions are described on a modulation transfer curve (MTF). To generate such a curve, contrast is plotted at various frequencies. Depending on the application, the highest resolution portion of the curve, may or may not be as relevant to the end user as sections of the curve that feature lower resolution at higher contrast. It really depends on what you're trying to do. For purposes of binocular astronomy, one could think of the difference between splitting close doubles, (which requires high resolution and magnification), and attempting to define a difuse light source such as a nebula.
Interestingly enough, the user's ability to perceive either, can be enhanced by limiting out select wavelengths via frequency blocking filters. Arguably, these filters limit resolution, (by blocking or limiting frequencies transmitted), but enhance contrast, and thus the users ability to discern detail.
In a nutshell, you need contrast for any resolution to occur, and you need resolution for contrast to be noticed. That's before we even get into a discussion about how the cones are best for sensing resolution, while the rods that we use for nightvision are better at sensing contrast and movement. The more I learn about all this stuff, the less I feel that I know. One thing I'm fairly confident about, though, is that all of the various components that go into binocular optics work together as a whole, and there is no one aspect that can really be regarded independently of the others.
Mike Swaim
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18" Starsplitter II f/4.5
8" Hardin Dob f/6
C5 workhorse mini SCT f/10 or f/6.3
70mm TV Ranger dual purpose birding/astro
77mm Leica Televid APO
16x70 Fujinons on UA Deluxe Mt.
12x50 Nikon SE
8x30 Nikon E2s
and many others
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lighttrap
Reged: 02/06/04
Posts: 3833
Loc: cloudy, foggy, humid NC, US
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These links may serve to illuminate or befuddle. Most of these articles relate more to microscopy and imaging, but many concepts herein may help illustrate why I currently am of the belief that contrast and resolution cannot meaningfully be separated by amateur astronomers discussing practical optical systems. I would suggest glancing through the first two articles to decide if they are of any help. The others get progressively more esoteric, and pretty much say the same thing.
http://www.edmundoptics.com/techsupport/DisplayArticle.cfm?articleid=289
http://www.licha.de/AstroWeb/articles_fullsize.php3?iHowTo=20
http://www.tvtechnology.com/features/Tech-Corner/f_RF_WhAT_IS_MOD.shtml
http://www.findarticles.com/cf_dls/m3125/8_72/62967906/p1/article.jhtml?term=
http://micro.magnet.fsu.edu/primer/java/mtf/spatialvariation/index.html
http://micro.magnet.fsu.edu/primer/java/mtf/airydisksize/index.html
The last 2 have interactive Java components which may or may not help or confuse.
Mike Swaim
--------------------
18" Starsplitter II f/4.5
8" Hardin Dob f/6
C5 workhorse mini SCT f/10 or f/6.3
70mm TV Ranger dual purpose birding/astro
77mm Leica Televid APO
16x70 Fujinons on UA Deluxe Mt.
12x50 Nikon SE
8x30 Nikon E2s
and many others
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nemo
sage
Reged: 06/09/03
Posts: 388
Loc: Eugene,Oregon
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Mike,
I can see that what I initially thought was a simple question was not. Obviously to give a detailed answer requires a more complex response. You have given me plenty to study. I am appreciative and as usual amazed at the level of expertise that this forum has.
R/S,
Dan
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"Humility is not thinking less of your self-it is about thinking of yourself less."
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lighttrap
Reged: 02/06/04
Posts: 3833
Loc: cloudy, foggy, humid NC, US
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Dan, when it comes to optics theory, nothing is simple. But, don't get bogged down in it. (This is supposed to be fun, remember? ;-) The more I learn about this stuff, the less I think I really "know". I'm still waiting for the time when I realize that I know nothing at all, including the fact that I know not even that!
Speaking of waiting on things, ... I'd love to read a very detailed report of those Miyauchi 22x71 "Saturns". Don't you also have some extra eye pieces for those?
Mike Swaim
--------------------
18" Starsplitter II f/4.5
8" Hardin Dob f/6
C5 workhorse mini SCT f/10 or f/6.3
70mm TV Ranger dual purpose birding/astro
77mm Leica Televid APO
16x70 Fujinons on UA Deluxe Mt.
12x50 Nikon SE
8x30 Nikon E2s
and many others
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brocknroller
Carpal Tunnel
Reged: 10/16/03
Posts: 1517
Loc: Liberal, Kansas
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Dan,
My approach is more experiential than technical. I've found that published resolution and contrast of a bin during the day or under ideal sky conditions has little to do with what I actually see under typical sky conditions where I live, which is close to a major university (with a google # of lights). A little moisture in the air, and the light dome grows and significantly decreases contrast, as if a bright moon were out that night.
For example, I've compared a nikon 10X35E2 to an Eagle Optics 10X50 Voyager ED, under less than ideal conditions (which is the rule rather than exception), and I can see asterisms and brighter messiers better with the smaller aperture bins than with the larger bins (I've also tested three other 10X50s against the 10X35s, but the EDs are the sharpest I've owned).
Since, in theory, a 50mm bin will out resolve a 35mm bin of comparable quality, the difference has to be in the exit pupil, which darkens the background sky and brings out stars and nebulae. So I agree with Mike, there is an important relationship between resolution and contrast that cannot be separated. It's similar to using filters for Mars. I have an 85mm APO refractor, and the views of Mars were pretty dismal until I bought some filters and was able to resolve features that I'd never seen before, because I increased the contrast.
The small exit pupil on the E2 (3.5mm) also corrects for my astigmatism, but I use my glasses with the EDs, so that should even out. I've recently compared the 10X50 EDs to Nikon 10X42 SEs, and they compare favorably. So it's not because the E2s have sharper optics or better coatings. I've also noticed a similar effect when using FMC 20X80s and 20X60s (4mm vs. 3mm).
Theoretical considerations aside, in practice I find the most important issue, other than good optics/coatings, in bin astronomy from my location, is the exit pupil of the bin. I would certainly prefer the 10X50 at a dark site, but from my backyard, the better view is from a smaller exit pupil bin.
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Oscar Zoroaster Diggs
"O.Z."
#########################################
"And remember, my sentimental friend....a heart is not judged by how much you love,
but by how much you are loved by others."
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KennyJ
Reged: 04/27/03
Posts: 10163
Loc: Lancashire UK
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Although no-one can disagree with the fact that all aspects of optical theory are very complex , I still think that many questions such as this one addressing the difference between Contrast and Resolution COULD be translated , diluted and simplified into layman's terms without losing the general gist of the matter.
What annoys me slightly is the fact that as soon as "optical theory" gets mentioned, the few people who really know about the subject instinctively dive in with complicated graphs and equations , advanced physics and mathematics , and a general assumption that the topic only applies to Telescopes and ASTRONOMY and those interested in those hobbies.
I am concerned with binoculars and DAYLIGHT TERRESTRIAL applications and I think MUCH could be explained by imagining hypothetical chess boards in a wide variety of contrasting squares ranging from black and white to two very similar tones or shades of grey ,placed at increasing distances from a binocular until the images gets so undefined as to be rendered NOT RESOLVED as a chess -board.
As such a test was carried out , as distance was increased one by one ,each binocular would be gradually eliminated from the test until we had the one that performs best in terms of contrast and resolution.
As each one is dropped out of the competition , it is logged as to it's maximum distance at which it was capable of resolving the object and eventually we end up with "league table" of the binocular performances.
So very simple , so very "un -scientific" , but so much more useful to laymen like me than a futile lesson in advanced physics and astronomy.
To me this presents another good example of the "mad scientist" syndrome --I meet them everyday in the universities I work in , the kind of guy who can quote and write nuclear equations blindfold , but cannot change a wheel,tighten a screw ,spell the name of the building he is lecturing in , or apparantly realise that his clothes and hairstyle went out of fashion before the majority of his students were even born.
I don't want to appear "boastful " but I'm very seriously and absolutely convinced that IF I really knew everything there is to know about the subject ,I could explain it in more easily understandable terms than any I've seen thus far
Regards -- Kenny.
--------------------
If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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Erik D
Carpal Tunnel
Reged: 04/28/03
Posts: 2570
Loc: Central New Jersey, USA
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Kenney,
I recall reading a Consumer Report comparsion of non-premium binos quite a few years back. I think 20+ binos under uner $500 were tested. The test methodology involved several testers reading newspaper prints at varying distance. The bino that could resolve news print at the longest distance received the highest rating. Consumer Reporters are not optical experts but to me that methond seemed to be ONE simple, logical, and measurable way of judging binocular resolution.
I believe an inexpensive pair of Nikon Verture(?) 8X23 received the highest rating using the test method above. Out scoring binos costing 2 to three times the price.
You may recall a gentleman posted test results on Astromart birding forum using the airforce test chart and 5 pair of binos in his collection late last year. Again a low cost model scored well. I don't remember the exact rankings but I think a pair of Leupold Winder River RP did very well. Do you recall the details?
Erik D
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KennyJ
Reged: 04/27/03
Posts: 10163
Loc: Lancashire UK
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Hi Erik,
As you know better than most , last year was a very busy one for me on the Astromart forums.
I really enjoyed the "buzz" of novelty surrounding the forum when we first got it separated from the photo forums , and an incredible number of varied discussions occupied my every thought for hours , days and weeks on end.
I have a vague memory of the post to which you refer but cannot recall the details.
What I can recall was becoming aware of the fact that the "resolution test cards" in question were probably no more useful when applied to the REAL world of binocular viewing than the newspaper print or my suggested "chess board".
And I also recall the cards being first published in 1959 or sometime around then, and feeling amazed that no further alternative testing devices nor serious research
on the subject seemed to have been carried out since.
By the way , on a related subject , the ( already controversial) article I promised is now available for criticism on the main CN articles page.
Regards , Kenny.
--------------------
If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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lighttrap
Reged: 02/06/04
Posts: 3833
Loc: cloudy, foggy, humid NC, US
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Kenny, if you want it all gelled and distilled, then consider this as one possible outcome:
Contrast defines how little resolution is necessary. While resolution defines how little contrast is perceptible. Magnification can, up to a point, increase both contrast and resolution.
I'm still considering whether that's entirely and always accurate. Likely not. Keep in mind that as with all things rendered gelatinous, there are some sticking points that get lost in the conversion.
Mike Swaim
--------------------
18" Starsplitter II f/4.5
8" Hardin Dob f/6
C5 workhorse mini SCT f/10 or f/6.3
70mm TV Ranger dual purpose birding/astro
77mm Leica Televid APO
16x70 Fujinons on UA Deluxe Mt.
12x50 Nikon SE
8x30 Nikon E2s
and many others
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KennyJ
Reged: 04/27/03
Posts: 10163
Loc: Lancashire UK
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Mike,
Perfectly accurate or not , I like it :-)
Just the kind of summary statement was looking for.
Regards --Kenny.
--------------------
If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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KennyJ
Reged: 04/27/03
Posts: 10163
Loc: Lancashire UK
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Mike,
Perfectly accurate or not , I like it :-)
Just the kind of concise statement I was looking for.
Regards --Kenny.
--------------------
If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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Resolution and contrast are not the same. An optical system can be optimized for one or the other, but not both at the same time.
Resolution is how small an image detail can be. Contrast is the degree of difference between two tones. Many people like MTF curves but are confused by what they represent. If you take a test target of black and white bars, resolution is how close those bars can be together and still be seen. Usually this is shown by a sine wave - the closer the peaks, the higher the resolution. Contrast is how black the black bars are and how white the white bars are. Using the sine wave again, the greater the distance between the peaks and troughs (the taller the wave), the greater the contrast.
Resolution comes in two flavors - angular resolution and resolving power. Angular resolution is applies to the object viewed and is a little tricky. It means nothing smaller than the angular resolution can be seen. However, bright objects like stars, if resolved, are the same size as the angular resolution. The Angular resolution is calculated by the aperture of the optics.
Resolving power is how many lines per millimeter can be resolved at the image plane. The image details cannot be any smaller than this. Resolving power is usually only applied to photographic systems. The resolving power is related to the effective focal ratio.
Angular resolution and resolving power is calculated based of the prime optical componant. It has nothing to do with eyepieces or anything else placed in the optical system.
The problem with resolution is that it changes with target contrast and brightness. It is not an absolute description for all conditions. The lower the target contrast, the lower the resolution of the system. Which means the Dawes limit is only applicable to bright stars, resolution of the scope is lower with nebula. The other problem with resolution is the subjective nature of most resolution tests - the results vary between testers. The non-subjective test, MTF, gives no information on image quality, but then the interpretation of the curve can lead back to a subjective judgement.
Magnification does not increase contrast or resolution of the OTA. Magnification can allow you to see image details below the resolution of your eye, but it always has a negative affect on both contrast and resolution. No free lunches in optics. 
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Anonymous
Unregistered
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Quote:
Kenney,
I recall reading a Consumer Report comparsion of non-premium binos quite a few years back. I think 20+ binos under uner $500 were tested. The test methodology involved several testers reading newspaper prints at varying distance. The bino that could resolve news print at the longest distance received the highest rating. Consumer Reporters are not optical experts but to me that methond seemed to be ONE simple, logical, and measurable way of judging binocular resolution.
I believe an inexpensive pair of Nikon Verture(?) 8X23 received the highest rating using the test method above. Out scoring binos costing 2 to three times the price.
You may recall a gentleman posted test results on Astromart birding forum using the airforce test chart and 5 pair of binos in his collection late last year. Again a low cost model scored well. I don't remember the exact rankings but I think a pair of Leupold Winder River RP did very well. Do you recall the details?
Erik D
I kind of agree, but there are two problems with the above. Firstly, as pointed out by Wilash, resolution varies with target contrast. High quality optics maintain resolution in low contrast situations e.g. at dusk, whereas cheap ones go to pot. Secondly resolution varies with distance, often quite dramatically. My Nikon 8x32 SE is not especially sharp at distances of ~4m, whereas it is awesome at distance of ~100m and greater. In my opinion sharpness is most important at large distances as then the bird will be small. Sharpness is less important at close distances, when the bird pretty much fills the field anyway.
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lighttrap
Reged: 02/06/04
Posts: 3833
Loc: cloudy, foggy, humid NC, US
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Quote:
Magnification does not increase contrast or resolution of the OTA. Magnification can allow you to see image details below the resolution of your eye, but it always has a negative affect on both contrast and resolution.
In a vacuum, or in a sterile and largely irrelevant theoretical sense, there may be a point there, somewhere. But, as for real world binocular (or telescopic) Earth bound astronomy, magnification (up to a point) very definitely does increase apparent contrast.
Try it yourself. Do a detailed comparison of a 7x50 and 10x50 for astronomy. In any environment other than extremely dark skies, the 10x50 will in fact show much more background contrast and will allow you to resolve more.
Mike Swaim
--------------------
18" Starsplitter II f/4.5
8" Hardin Dob f/6
C5 workhorse mini SCT f/10 or f/6.3
70mm TV Ranger dual purpose birding/astro
77mm Leica Televid APO
16x70 Fujinons on UA Deluxe Mt.
12x50 Nikon SE
8x30 Nikon E2s
and many others
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nemo
sage
Reged: 06/09/03
Posts: 388
Loc: Eugene,Oregon
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Mike,
In regard to the Saturn Miyauchi 22x71's the weather has not been cooperating. Since I received them there have been only about 2 nights where the atmosphere has been even close to decent and on those occasions I was other wise disposed. Here in the Pacific Northwest we have been having lots of rain, which is normal. As we get into the Spring time patterns there should be little envelopes of clarity between storm systems which I hope to take advantage of. I have had a chance to do a little daytime observing and what has impressed me so far is that these bino's seem to just "Snap in to focus". I am anxious to try these things out .Will try to post something when I do.
Take care,
Dan
--------------------
"Humility is not thinking less of your self-it is about thinking of yourself less."
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KennyJ
Reged: 04/27/03
Posts: 10163
Loc: Lancashire UK
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As I had hoped it would , this debate is getting more interesting (to me at least) every day.
The previous three posts from Wilash , Mouse and Swaim (which has the ring about it of a rather eccentric partnership of solicitors :-)) -- whilst slightly conflicting ,have each in their own ways contained points of great value and relevance to the discussion.
Much as I admired most of Wilash's informative post ,I almost join forces with Mike Swaim with regard to the assertion by the former that "magnification always has a negative effect on both contrast and resolution"
Whereas Mike S expressed disagreement specifically with the assertion that magnification negatively affects CONTRAST
( at least in practical / reality situations ), I take issue with the statement in it's entirety ,as far as my own practical experience has shown.
Specifically as a direct result of reading these three posts
some four hours ago from the time of writing , when it was very conveniently "twilight" here in Northern England, I grabbed four pairs of binoculars and went out in the back yard to try a few things out ( and ended up out there for over two hours with telescope added to the four binos to enjoy the clearest night sky I've had the pleasure of being under since New Year ! )
But before it turned completely dark I carried out numerous tests comparing what I could see naked eye and what I could see through each of the four binoculars , which were Swarovski 8 x 20 , Zeiss 7 x 42 ,Swift 10 x 50 and Helios 15 x 70.
Without a shadow of doubt , each and every one of these binoculars greatly improved details ( in terms of contrast and resolution )over what I could see with naked eye.
The easiest example to quantify was what appeared with naked eye to be a vaguely off - white oblong shape about 7 feet above ground level against a nondescript brown wall roughly 40 yards away.
When viewed through ANY of the binoculars, this proved to be a sign bearing the words "DANGER Of DEATH above a triangle shape containing a symbol of sorts below which were the words KEEP OUT.
Through all of the binoculars the wall to which this sign was attached was clearly discernible as being of brick construction. Not so through naked eye.
The Zeiss 7 x 42 clearly showed the sign to be YELLOW in colour with BLACK wording , the Swarovski 8 x 20 not so.
The 10 x 50s and 15 x 70s showed the sign to be yellow in colour , but not as obviously so as the Zeiss.
The 10 x 50s showed the symbol in the triangle to contain, along with some other indefineable shape, the zig -line of a LIVE VOLTAGE warning symbol, which was visible but mistakeble through the Zeiss 7 x 42s and which was visible through the 8 x 20s whilst being indiscernible as a separate item from the rest of the "squiggly shapes" inside the triangle.
Only through the 15 x 70s could I also make out that within this triangle, below this zig -zag symbol, was a rather Lowry -like artistic impression of a human-being in the process of being electrocuted.
About 15 minutes later , only the Zeiss 7 x 42s appeared to present an image comparable to what had been presented earlier through respectively speaking.
This is to suggest that the apparnt "advantages" described above of both magnification and increased objective size, seemed to wither almost in direct proportion to the fading of natural light.
As the natural light reduced I got the impression that the 6mm exit -pupil at 7x magnification was , for some reason providing an image much brighter and more easily discernible than both the 5mm exit -pupil at 10x and the 4mm exit -pupil at 15x -- and this was much more marked than I had expected, and arguably quite contrary to accepted theory applying to "twilight factor" as I understand it.
The bottom line is that if these binocular observations do NOT represent an improvement in terms of both resolution AND contrast , then I am clearly misunderstanding the definitions of BOTH.
Regards -- Kenny.
--------------------
If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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KennyJ
Reged: 04/27/03
Posts: 10163
Loc: Lancashire UK
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Mickey wrote :
<Secondly resolution varies with distance>
This is something I also claimed to be evident from my own "practical tests "in more than one post over on the Astromart "birding optics" forum several months ago , but another one of my claims that received little more than ridicule from the "properly educated" factions of that place so strangely inactive of late.
Almost all "explanations from above" on those occasions revolved around the very real factor of "mirage".
But I maintain there are other factors involved here , one of which I am becoming increasingly convinced is "aperture" or objective size.
I am almost certain that the improvement I perceive in an image , for example with a 10 x 50 as compared with a 10 x 25, becomes increasingly pronounced as distance between viewer and viewed object is increased.
Both "Birders" and "Astronomers" tend to carry out most of their binocular observations at distances from their intended visual targets that are actually quite different from many of those of my own.
Somewhere between the Robin at ten feet, the Heron at 500 yards and M31 at 2000 Light Years is a rarely mentioned type of binocular user who is looking for the best image obtainable of objects which lie quite distinctly somewhere within the 500 yards and millions of miles.
Medium to long distance buildings ,boats and landscapes, aircraft and satellites are three very good examples which spring to mind, and which are just as interesting to observe for me personally as are birds, stars or faint fuzzies.
Whilst my wife's Swarovski 8 x 20 can, in certain conditions, provide remarkably sharp , bright and clear images for such a pocket -sized instrument,both for "birding" and "astro" distances , for a reason which I can only contemplate MUST be related to it's diminuitive aperture ,it just does NOT perform as well as does my Zeiss 7 x 42 when used for these "medium to long range" purposes.
I seek opinions on two possible causes here.
1. Is this REALLY because of the small objectives per se ?
2. Is it related to EXIT -PUPIL ?
And of course -- if so -- WHY ?
Regards -- Kenny.
--------------------
If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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KennyJ,
First about resolution. Resolution is the main optics ability to differentiate between object details. It has nothing to do with what you can see or the eyepiece. The problem with the word "resolution" is that it has different means in optics and in observing. For example the following two sentences are not the same:
A XX" scope can resolve XXarc seconds
I could resolve a double star at 100X.
The equations for optical resolution are not related to magnification and therefore it has nothing to do with eyepieces. The resolution is what the main objective can acheive, whether we can see it or not. The eyepiece magnifies the aerial image, but if the detail is not in the aerial image, the eyepiece cannot add any. The resolution of the aerial image is fixed. So when I look at the moon at 25X with my telescope I can only see large details - a limitation in my eye. If I increase the magnification, I can see more, but I have not changed the detail in the aerial image, I have simply magnified it to the point that my eye can resolve the details.
The resolving power of a system (here again it has nothing to do with magnification or what you can see) can be calculated. Simply add the reciprocal resolving power of each componant to find the reciprocal resolving power of the system. This means the resolving power of a system is always lower than the resolving power of any of its componants. So when you add eyepieces and barlows and diagonals to the objective, the resolving power of the system decreases. Here are again, this has nothing to do with visual response.
Now this is what gets me into trouble with visual observers. As magnification increases, contrast and resolving power decrease. This has to do with the effect of increasing the effective focal length and effective focal ratio of the system. You can actually see the effect with a telesope. Look at the moon with increasingly higher magnification. The difference in luminance between the bright areas and dark areas get closer. Sharp lines of craters become thicker and softer. But I will leave this subject for now because I'm sure someone will object and then I will got into some of the ways to explain it. Also this post is getting long.
Now for "resolution" as a term for visual response and your second post. As long as the resolution of the optical system is great than the resolution of the eye, the images should APPEAR sharp. Binoculars rarely work at powers where the limits or resolution can be seen. The quality of the optics withstanding. Also the effect of magnification to increase image size, means you can see more detail, but it has nothing to do with resolution in an optical sense. Magnification is important for our visual response. And so here is the problem of taking optics as an absolute statement and always comes down to a subjective judgement. What compromises will we make to create an image that is pleasing to the eye?
The distance question is a little more complex. The resolution of an optical system does change because the effective focal length and focal ratio increase as you focus closer. But at the distances you are talking about, this will have very little effect. The other reason would be the atmosphere. The more air you look through, the lower the resolution - the atmosphere can be thought of as an extention of the optical system, zero power, but impacts resolving power (see above about calculating the resolving power of a system). Since the larger optics have greater resolution than small ones, the loss of resolution because of the atmosphere accentuate the limits of the smaller binos.
The comment that resolution decreases with distance is difficult to explain. I would want to see the binos to see if it is another problem relating to abberations or something else.
I think we need a 25-word limit on questions and answers. 
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