Importance of size of exit pupil

[gunvald]

Dear all!

One thing that surprises me with this excellent forum is the little amount of discussions about the need of a large exit pupil. This is always pointed out in theory and advertisments.

I am to buy a pair of good binos and have looked through binoculars mainly in shops and on photo exhibitions, that is, in good light and, of course, at a steady ground and with no wind. I have looked mainly at 8x30 and 8x42 binoculars from Zeiss, Swarovski and also Leica. Everything looks good in those conditions due to the forgiving conditions where the pupils of the eye are small.

What are your thoughts on this matter when using binoculars in practice, especially at dawn and dusk? I exclude usage in a boot at sea and in strong winds where it is difficult to hold the binoculars steady. I am mainly talking about "good" viewing conditions when you can place and keep the eye in a good position relative to the eye pieces of the binoculars.

To clarify what I mean, I have read some posts about the Nikon SE-s (with 4 mm exit pupil) where several people concluded that they in low light can see as much with a pair of SE-s as with a pair of top notch 8x40/8x42/8.5x42 binoculars (with around 25 % larger exit pupil which equals about 50 % more light transmission). Most comments are about differencies in physical appearance between the porros and the roof binos, but very few seem to care about the differencies in exit pupil.

According to several sources, the pupil in the human eye dilates to a maximum of about 6 mm in diameter in low light for "younger" persons (perhaps under 30), while for people over 50, the dilation tends to stop at around 4 mm.

I have come to think that people over 50 may not care about if they look through a pair of 8x32-s or a pair of 8x42-s in terms of exit pupil. Perhaps those who are now selling their 7x42-s to buy e.g. 8x42-s or 8x32-s instead have become older and no longer really need more than 4-5 mm in exit pupil?

One conclusion is then that the Nikon SE binos are better suited for those over about 40 and to a lesser degree for me (who is 34) if the intention is to find binos for low light usage.

Any thought on this? Is there anyone with deeper insights in human vision who might share their expertise?

[mpedris]

An excellent question, gunvald. I am planning to buy a pair of 8x32 SEs. I'm 33. I wonder if I'll have problems with its exit pupil diameter in low light situations.

I sincerely hope a knowledgable somebody will shed some light on this!

[Leif]

Dear all!

One thing that surprises me with this excellent forum is the little amount of discussions about the need of a large exit pupil. This is always pointed out in theory and advertisments.

I am to buy a pair of good binos and have looked through binoculars mainly in shops and on photo exhibitions, that is, in good light and, of course, at a steady ground and with no wind. I have looked mainly at 8x30 and 8x42 binoculars from Zeiss, Swarovski and also Leica. Everything looks good in those conditions due to the forgiving conditions where the pupils of the eye are small.

What are your thoughts on this matter when using binoculars in practice, especially at dawn and dusk? I exclude usage in a boot at sea and in strong winds where it is difficult to hold the binoculars steady. I am mainly talking about "good" viewing conditions when you can place and keep the eye in a good position relative to the eye pieces of the binoculars.

To clarify what I mean, I have read some posts about the Nikon SE-s (with 4 mm exit pupil) where several people concluded that they in low light can see as much with a pair of SE-s as with a pair of top notch 8x40/8x42/8.5x42 binoculars (with around 25 % larger exit pupil which equals about 50 % more light transmission). Most comments are about differencies in physical appearance between the porros and the roof binos, but very few seem to care about the differencies in exit pupil.

According to several sources, the pupil in the human eye dilates to a maximum of about 6 mm in diameter in low light for "younger" persons (perhaps under 30), while for people over 50, the dilation tends to stop at around 4 mm.

I have come to think that people over 50 may not care about if they look through a pair of 8x32-s or a pair of 8x42-s in terms of exit pupil. Perhaps those who are now selling their 7x42-s to buy e.g. 8x42-s or 8x32-s instead have become older and no longer really need more than 4-5 mm in exit pupil?

One conclusion is then that the Nikon SE binos are better suited for those over about 40 and to a lesser degree for me (who is 34) if the intention is to find binos for low light usage.

Any thought on this? Is there anyone with deeper insights in human vision who might share their expertise?

Maybe others are too busy birding to discuss this, but you make interesting points. There were some discussions about this on the Astromart forum. Apparently it is not a foregone conclusion that old people have small dilated pupils, and 7mm or more is not uncommon. Similarly young people can have small dilated pupils. I will try and find a link to the graph that I once saw.

I compared the Nikon 8x32 SE with the Swaro 8.5x42 EL and cannot distinguish between them in terms of brightness at dusk and on the night sky. However, I am 40 years of age, and I have not had my pupils measured, so it is possible that I have pupils that do not dilate more than 4mm.

I do find that I prefer to use the Swaros in low light, not because they show more - they don't - but because the larger exit pupil makes it easier to align the binoculars with my eyes. I suspect that a 7x42 binocular would be even better though these seem to be not so popular these days.

I suspect if you ask Scampo what size his pupils are he will say "between 5 foot and 6 foot 5 inches". That's Slough humour. (Scampo is a teacher.)

[Leif]

There's a nice graph on page 7 of the following PDF:

http://www.btow.com.au/pdf/agwa/agwa-September-2003.pdf

It confirms that as you say the tendency is for the dilated pupil size to shrink with age, but there is also a large spread.

[mak]

If you use your binocular at dawn and dusk, I would say that you require a minimum of 4mm exit pupil diametre from your binoculars.

7mm is the maximum size that the human pupil will achieve and this is found (as a general rule) in younger people. So if you are for instance in your mid 50s (I just picked an age, so lets not make an issue) and that person has an eye pupil of 5.6mm, you would not receive the full benefit if you owned say an 8x56 binocular (exit pupil of 7mm).

You would receive the full benefit if you owned a 10x56 (exit pupil of 5.6mm). If the person had a pupil of + 6mm then the 8x56 might be a better option.

As a guide, should you wish to purshase binoculars for use at dawn and dusk then look at these two parameters.
1: Geometric light gathering of no less than 16 (exit pupil of 4mm x 4mm = 16) and
2 An objective lens of no less than 40mm.

This is only a guide as it does not say anything about the manufacture, prism system, coatings or glass types.

[scampo]

It all sounds very interesting. It is in woodland at dusk that this is most likely to be of any importance - and I cannot say that I have noticed much difference between high quality bins in those conditions. The Nikon 8x42, Swaro 8.5x42 and Optolyth 10x40s all seem to my now 50-year-old eyes to give a similarly bright view - even thought the Optolyths shouldn't. Odds bodikins!

I doubt that the pupils in the eyes reach their maximum size until it is far too dark to watch for birds, though.

An interesting thing, Leif - the Nikon scope and the Nikon HGs are surprisingly similar in the qualities of their images - as are the Swaro bins and my son's Swaro 65 scope. The manufacturers must work hard on this, I should think.

[mak]

I doubt that the eyes pupils reach their maxima until it is too dark to watch for birds, though.

Most probably.

[Carson]

It's a very important point, but I think the reason you may have heard little about it, is, as this thread suggests, that the variables have become incalculable. I say "become" because exit pupils were relatively easy to factor in through the 1970s, at least.

The math and physics haven't changed, but the technology has.

By the time you purchase any very good optics now--and I am speaking here of only the best--you realize there's a point you step across where you simply believe that this manufacturer does indeed produce the "sharpest" optics--and that is a combination of trust and subjective impression.

As far as I know, the only way to test for your own personal benefit from the light-gathering virtues of various binoculars or telescopes is to actually test them in end-of-day lighting conditions.

That is not easy, but neither is it impossible, as a small birding group of fairly elite birders might well be equipped with a pretty impressive group of fairly elite optics. I was able to borrow a companion's binoculars for half an hour in the field before I bought the same model.

Might I suggest an outing with others interested, just to compare equipment? I would think there are as many people willing to show off their optics as there are people interested in purchasing very good optics. Naturally, some people prefer never to lend; and that must be respected.

But also, if you do happen to drop a pair of borrowed binoculars worth as much as your new car, this might be an excellent moment to remember the debt your best friend never repaid you, and give his name as yours while promising to pay for all damages.

If you stick with theory, though, I'm afraid you might cover several sheets of paper with figures, and you WILL become very knowledgeable, but, really, your conclusions will be as blurry as a pair of bad binoculars.

[scampo]

Meet up? Leif suggested the same - gosh Leif and you could meet half way - say, Iceland. Can I come, too? Could be a good day out!!

(-:

[Leif]

An interesting thing, Leif - the Nikon scope and the Nikon HGs are surprisingly similar in the qualities of their images - as are the Swaro bins and my son's Swaro 65 scope. The manufacturers must work hard on this, I should think.

I know what you mean. When I tried the Nikon scope I was struck by the similarity of the image in terms of its 'feel' to that produced by the 8x42 HG. I noticed a similar thing for Swaro and Leica. It could simpy be the use of the same coating technologies and glass types, or maybe they each have their own idea of what constitutes an ideal image?


gosh Leif and you could meet half way - say, Iceland. Can I come, too?


I think I'll stick to the local RSPB reserve, and InFocus field days if that's alright with you!


If you stick with theory, though, I'm afraid you might cover several sheets of paper with figures, and you WILL become very knowledgeable, but, really, your conclusions will be as blurry as a pair of bad binoculars.


Very true. I don't think it's hard for most people in the UK to find a suitable place to test and compare a couple of pair of bins or scopes. Many shops - for example LCE, Kay Optical, InFocus, Cley Spy, RSPB spring to mind - provide field days and/or excellent viewing facilities. I don't think it's too hard to buy in Winter, and try the items at both mid-day and sunset, though the salesmen at some shops might be a little puzzled. They will be smiling if and when you walk out the door with a new toy.

[gunvald]

Thanks for your thoughts and thanks to Leif for the interesting pdf file you supplied.



As far as I know, the only way to test for your own personal benefit from the light-gathering virtues of various binoculars or telescopes is to actually test them in end-of-day lighting conditions.

I prefer to make my decisions in a two-step manner, with one somewhat theoretical first step (this puts some people off) where information is collected and my candidates are selected. Then a practical hands-on assessment comes next, where I know better what to look for, this is also when the subjective "feel" factor comes in. In my point of view this strategy takes patience and time, but I find it to be a good way to a good decision, since first or even second impressions might lead you wrong. At least this is the case in selection of, say, a medium format camera system if you are used to 35 mm cameras.

Anyway, now time has come to act. A pair of used Zeiss 7x42-s are on their way. I am also going to order a pair of Nikon SE 8x32-s. I have the right to return within a week and should be able to do some good comparative tests. Yes, these binos are indeed different, and I migh end up keeping both, one pair rather light-weight for my camera bag and one for good viewing in low light. At first, I planned to buy a pair of 8x42-s and even had a pair of Nikon HG-s on order, but then started to think in new directions.

[Jonathan B.]

I have read about eye dilation decreasing with age, usefulness of large exit pupil consequently being wasted on older eyes, etc., for years. As Leif says, there has been much discussion of this on the Astromart forums, specifically on the forum, "Birding Optics, No Pictures." That forum should actually be called, "Birding Optics, No Birding," because it is predominantly written by people who stargaze and tends to be more theoretical than practical. After months of finding no useful information on it I quit reading it.

In situations where one is using binoculars in open sunlight, notably birding, how could one expect their eyes to be fully dilated? I have to believe that focusing a light source on the eye causes the pupil to constrict. Stephen Ingraham has mentioned this indirectly in several reviews--that a 4mm exit pupil will provide a sort of optimum daytime light level. I don't know if he has scientific reasons to propose this; I suspect he learned it from experience. I find this to be true using various binoculars. An 8x20 definitely provides a dimmer image in open sunlight than an 8x32, but a 7x42 does not provide a brighter image than an 8x32. My eyes dilate to at least 6mm in dim light, so they are capable of using the larger exit pupil.

It seems to me that the usable exit pupil concept derives from astronomical use of optics, and not from daytime use. I welcome any clarification.

[Carson]

Yes, Jonathan, a local astronomer told me he is quite sure it takes the human pupil a good half hour to open fully. He suggested it opens gradually, but closes, or begins to close, quickly in reaction to a sudden blast of light ("light pollution"--such as headlights--to astronomers).

Similarly, traditional slide shows, clicking from one slide to the next, cause the audience's pupils to do pushups (!) as they continually begin to open and close in response to the dark-light-dark-light changing of the slides. Your audience's sleepiness is not just because you've shown too many pictures of Aunt Bertha's children--it's also because of all this wearisome eye exercise.

-- If you would like to improve your slide show, you need two projectors and a dissolve unit. The slides alternate, projector A-B-A-B, via the dissolve. There is no half-second of blackness between pictures. Dissolve times can be set by the projectionist, but the point is that each slide dissolves into the next without undue change of illumination on the screen. This is a MUCH more pleasing slide-show, and your audience stays much more awake. --Um, unless you insist on still showing too much of Aunt Bertha and the kids.

A cheap pair of 7x35 binoculars, despite their 1:5 power:objective lens ratio, will admit way less light than very fine optics in, say, an expensive pair of 10x42 binoculars. You could actually drop to a 1:4 ratio or worse, and, if the glass were very high quality, you would still have more light. This confounds the numerical comparison.

People reading this thread, who have both cheap and high quality binoculars, may find this interesting: hold your binoculars in the usual position, but about 2 feet out from your eyes, in good light. Your expensive binoculars will show, within the eyepieces, exit pupils that are perfect, brilliant, uninterrupted circles.

-- Now do the same thing with your cheap binoculars. The inside edges of your exit pupils will be interrupted by a very pale gray straight-line "cut" representing a triangle. Look carefully, and you will see it. This is the relatively small prism disallowing the exit pupil its true, theoretical size.

Because the prisms are smaller, the binoculars are cheaper, and they also weigh less. Larger prisms make good binoculars somewhat heavier.

We have been discussing high-priced optics in this thread. If, however, you are quietly reading this and lamenting your modest budget, take heart: an older pair of 8x40 binoculars will still let you become an expert birder, and will give you beautiful views. But DO test out the focus wheel (knob) carefully: in cold weather, if the focus becomes very stiff, your binoculars will work against you. You may also find a good buy second-hand, but you must look for binoculars that have either been used very seldom or else have been pampered. If they are dirty or their exterior indicates rough use, they may have been knocked or dropped. Once the alignment of the lenses inside has been jolted out of true, these binoculars will never be the same again--and, after repairs, they will no longer be a cheap pair of binoculars. If you are buying on a low budget, take your time. I have seen fabulous buys made by people who haunted thrift sales and such for perhaps a year or so.

Apologies for my too-lengthy postings. Someone else may wish to explain the Interesting Case of the More Distant Duck, in which a wonderful principle of physics makes the far end of a picnic bench, viewed through binoculars, flare out wider--or the same-sized bird BEHIND seem to be larger than the one in front! (But I'm bowing out. Thank you.)

[Leif]

I've found optical quality to be far more important than exit pupil size, although as mentioned, I certainly would not go below a 4mm exit pupil.

I bird a lot after work, and so prefer binoculars that can be used at dusk up to the point where I go home because I can no longer see clearly with the naked eye. Cheap 8x40 binoculars are just not up to the job and give up the ghost long before my eyes. Most 8x32 binoculars aren't up to the job either. The Nikon 8x32 SE and 8x32 HG are the exceptions. My preference for low light use is a high quality 8x42 binocular with its 5mm exit pupil that makes for comfortable viewing. However, as with all things, there's a lot of subjective judgements here, and some people will come to different conclusions, prefering perhaps the Leica 8x32 BN or the Zeiss 8x56 Victory!

Low light is when you realise that there is a reason why you paid a small fortune for a pair of binoculars.

[Jane Turner]

The factor which I find most important in exit pupil size is the degree of shake/wind vibration etc you can take without reducing the quality of the image...

I have Leica 8 x 20's and 8x42's In good light and with the bins resting on a surface you'd be hard pushed to tell them apart..... but in a NW10, looking for petrels out of a wind buffeted car its blindingly obvious!

[Swissboy]

The factor which I find most important in exit pupil size is the degree of shake/wind vibration etc you can take without reducing the quality of the image...

I have Leica 8 x 20's and 8x42's In good light and with the bins resting on a surface you'd be hard pushed to tell them apart..... but in a NW10, looking for petrels out of a wind buffeted car its blindingly obvious!

I agree. And the reason why this is important is because a larger exit pupil allows for some movement between yourself and your optical device (binoculars or scope) without losing sight of that magnified image. For this reason, a large exit pupil even helps when your own eyes' pupils can't open up that much any more.

[scampo]

But with a dilated pupil, the eye's ability to see detail falls dramatically. The retina gives of its best only when the pupil is small.

[Carson]

Scampo, I didn't know that, and I find it fascinating. The smaller the aperture (ie. f-stop) in a camera lens, the greater the depth of field. In wildflower photography, a flash is often used in daylight to allow for f16 or f22, and hence a very detailed picture for technical botany use. If the same picture were taken at f8 (at which the lens is much more "open"), much less of the flower would be in critical focus.

Scampo, are you saying, then, that our eyes work along exactly this same principle? Is it simply a dictate of physics?

[scampo]

I think it fair to view the eyes as simply a lens with a diaphragm (i.e. the iris), so all the rules apply.

[Leif]

I think it fair to view the eyes as simply a lens with a diaphragm (i.e. the iris), so all the rules apply.

I heard that when the iris dilates irregularities in the shape of the cornea become more apparent. I know from first hand experience that the cornea is remarkably sensitive. A year ago I got some small splinters in one cornea, that caused it to swell, producing marked astigmatism.

I seem to recall that when the eye dark adapts, it produces a chemical that aids light detection. Exposure to bright light destroys the chemical and hence dark adaptation is lost. I guess this level of low light sensitivity is not that relevant to birding, though last night well after sunset I was surprised to hear a swan fly past. Goodness knows how it sees pylons and HT cables.

[Jay Turberville]

I think it fair to view the eyes as simply a lens with a diaphragm (i.e. the iris), so all the rules apply.

Yep. But that means you have to get down to the nitty gritty and work out the details of what is the optimal f-number for the human eye. There may be a point where an even smaller sized iris begins to hurt image sharpness. This will depend on the spacing of rods and cones and how well the eye's lens is corrected. If we know the density of the sensors on the retina, we could compute the iris size where our eye would become by diffraction from the iris. Optimal would probably be an iris size somewhat large than that depending on how well corrected the person's particular vision is.

The optimal f-number for a camera or camera-like imaging system will vary depending on factors such as these. Most 35mm camera lenses will not stop down past f22 because they are diffraction limited at around that point. Most give optimal resolution and sharpness at between f5.6 and f11. Shooting at f22 may give a greater DOF, but it does so at the cost of image sharpness. The "sweet spot" varies depending on the quality of the lens.

Typical digital cameras don't stop down further than f10. This is because they become diffraction limited at around f10 - a different f-number than for 35mm cameras. For instance, my CP5000 won't stop down further than f8. Digicams have a very much narrower "sweet" spot for optimal sharpness. Probably around f5.6.

http://www.jayandwanda.com/digiscope/digiscope_calc.html
If you plug in 1X on the calculator, you can calculate optimal f-numbers for the camera by itself. We can see that a CP4500 becomes diffraction limited at around f10. Optimal will be somewhat below f10.

The typical focal length of a human eye is 17mm. So a 4mm iris is a bit wider than f-4. If it is 2mm in bright light, then we typically see at around f8. If we knew the density of the eye's receptors, we should be able to enter the eye as a camera in the calculator and figure out when it is diffraction limited. Our optimal iris size should be a bit larger than it size when diffraction limited.

[mpedris]

WOW! A whole new dimension of thinking...

[mak]

[QUOTE=Carson]
People reading this thread, who have both cheap and high quality binoculars, may find this interesting: hold your binoculars in the usual position, but about 2 feet out from your eyes, in good light. Your expensive binoculars will show, within the eyepieces, exit pupils that are perfect, brilliant, uninterrupted circles.

-- Now do the same thing with your cheap binoculars. The inside edges of your exit pupils will be interrupted by a very pale gray straight-line "cut" representing a triangle. Look carefully, and you will see it. This is the relatively small prism disallowing the exit pupil its true, theoretical size.[QUOTE=]

I dont know about cheap, but I have seen a £300+ pair of binoculars, with this feature, even a diamond shape within the exit pupil. A classic case of "shaved" prisms, and it is a sign of poor manufacture. £300, not worth £25.

[Jay Turberville]

I think it fair to view the eyes as simply a lens with a diaphragm (i.e. the iris), so all the rules apply.

I found this as a follow-up.
http://www.spie.org/web/oer/october/oct97/eye.html

Using the supplied spacing for cones, I entered the info in my calculator and the typical human eye does become diffraction limited at around a 2mm iris or f8. This would be 200 lp/mm or almost twice what the above author shows for a 3.5mm iris in his model. So it seems that the optics of our eyes is the main limiter and that "stopping down" further - probably all the way to f8 will continue to improve perceived sharpness and resolution.

[Swissboy]

IGoodness knows how it sees pylons and HT cables.

Well, they often don't. Even owls get caught by cables. These kinds of things - just like window glass - are not part of the original nature. And thus, no adaptations have been able to occur.

[Jay Turberville]

A cheap pair of 7x35 binoculars, despite their 1:5 power:objective lens ratio, will admit way less light than very fine optics in, say, an expensive pair of 10x42 binoculars. You could actually drop to a 1:4 ratio or worse, and, if the glass were very high quality, you would still have more light. This confounds the numerical comparison.

The 1:4 ratio seems just incredibly unlikely to me. Do you have any kind of reference for this?


Your expensive binoculars will show, within the eyepieces, exit pupils that are perfect, brilliant, uninterrupted circles.

-- Now do the same thing with your cheap binoculars. The inside edges of your exit pupils will be interrupted by a very pale gray straight-line "cut" representing a triangle. Look carefully, and you will see it. This is the relatively small prism disallowing the exit pupil its true, theoretical size.

Because the prisms are smaller, the binoculars are cheaper, and they also weigh less. Larger prisms make good binoculars somewhat heavier.


I have three pairs of binoculars (pairs?). None would be considered very good birding binoculars. I have a Nikon 9x25, a pair of "zoom" binoculars from Sharper Image 7-15x25, and a pair of super cheap 10x25 Vanguard binoculars (purchased from Fry's electronics so I have something to hand kids when they visit).

The Nikons have perfect circular pupils. The zoom pair has squarish exit pupils. And surprisingly, the supercheap 10x25s also had perfect circles for exit pupils.
I found this site that explains the squarish exit pupils as an artifact, not of a small prism, but of the use of BK7 glass in the prism as opposed to the better BAK4 glass.
http://www.monkoptics.co.uk/General/binocularterms.html

But I looked backwards through the Sharper Image binoculars and noticed physical structures that also contributed to the some of the aperture blockage along the bottom of the light path.

The sun was setting, so I decided to do some side-by-side comparisons of these three binoculars in failing light. I came to some rather interesting conclusions. The Nikons seemed to be the brightest, the Vanguards next and the Sharper Image pair seemed quite a bit dimmer. So my first conclusion was that yes, the occluded exit pupil had a real and noticable effect.

But I further noticed that the SI (Sharper Image) pair had a distinctly unnatural color cast. We had a bright purple pink color in the sky as the sun was setting and the SI pair almost completely neutralized it. Big surprise - I looked at the front objective and their coating was distinctly ruby-red. The color cast in an antireflective coating must come from somewhere. In this case, it is very strong and apparently comes from the coating rejecting red light. This results in a very cyan colored image.

I then put one side of the SI pair to one eye and the Nikons up to the other and compared the brightness by alternately closing and opening my eyes. Hmmm... There really wasn't that much apparent brightness difference when viewed side by side. But there was a huge FOV difference. The Nikons seemed to give a pretty wide view while the SI pair was like looking down a tunnel. The pink sky looked brilliant and natural through the Nikons, but the SIs made the sky dull since they were acting like a red filter - just the opposite of looking at the world through rose colored glasses. This was probably the worst kind of light for these binoculars.

The AFOV of the Vanguards was actually wider than the Nikons. Subjectively, they seemed to be brighter than the SI pair. But objectively, there was little difference in the brightness of non-reddish colors. But that large AFOV really made them open up the view and there was a clear psychological impression of a brighter view.

So in the end, it seems to me that FOV has a lot do do with the impression of brightness. And strong color casts may very well have a similar phsychological effect in addition to the actual light loss that such a strong cast implies. Wide views are just more pleasant to my eyes.

I've always automatically just grabbed the Nikons when going out digiscoping, but I never bothered to compare them to the other two pairs. I'll keep grabbing them until I can justify purchasing a good birding pair. I think I'll let visiting children use the Sharper Image binocs from now on (they should enjoy the zoom) and I'll put the super cheap Vanguard's in the glove box where they will certainly be abused but might be handy to have available from time to time. Their view is far nicer than the Sharper Image pair and not that far off of the Nikons.

[henry link]

This reply is to post #24 in this thread.

Eyesight resolution can also be specified in the way same way as telescope resolution, as seconds of arc. The usual figure given is 60 arc seconds which corresponds to a diffraction limited aperture of 2mm.

This has some implications when trying to judge the true resolution of a scope or binocular. The arc second resolution of the optic multiplied by the magnification must be equal to or greater than 60 arc seconds or the eye will be the limiting factor. For example, 2 arc-seconds of resolution requires at least 30x.

An 8x binocular with 3 arc-seconds of resolution presents the eye with an image of 24 arc-seconds of resolution, more than twice as good as eyesight resolution. The only way to see the true resolution of this binocular is to place a small telescope of at least 2.5x behind the eyepiece to boost the magnification.

[laika]

I have three binos Fujinon 7x50FMTR-SX2,Zeiss Victory II 8x40 and Leica Ultravid 10x42BR. Fujinon is brightest,Zeiss next and Leica is the darkest one.
When testing them at night i can see most details with my Leica and fewest with Fujinon.So i wonder is the word brightness a bit overrated ?

[scampo]

Quite clearly, brightness in itself is not the be all and end all, as your experience has determined. What a shame you don't have the Fuji's brightness with the Leica's clarity...

[gunvald]

Hi Laika!

Which binoculars let you see colour and colour hues with the greatest ease? Is it still with the Leicas or do the Fujinons and Zeiss Victorys perform better?

I have on test a pair of Nikon SE 8x32s and a pair of Zeiss 7x42s (old ones without P-coating). The Zeiss binos are with no doubt brighter than the Nikon SEs and let me see colours and colour hues with very good rendition in very low light where the Nikon "just" shows the details. Some very fine details almost get lost with the Nikons.

Perhaps it is stupid to compare the Nikon SEs with the Zeisses, especially with the reputation the Zeisses have for brightness. They are also different in magnification and objective lens diameter that should put the Zeiss on top.

Still, I feel a little disappointed with the Nikons. I thought they would be less bright but with a little more punch in contrast to compensate. I also find it hard to really see the difference in magnification between the two. The Zeisses are not faultless, they distort the image at the edges and the sharpness drops towards the edges. They also give the image a disgusting slight green colour cast. The Nikons have a much better colour rendition.

My problem is that I have no any other 8x binoculars at hand and cannot compare the SEs with other binoculars of the same magnification. If I could, I might praise them. On the other hand, judging from my tests I should be able to cope with 7x as well as 8x.

How many of you have tested the Nikon SE 8x32 side-by-side with Leica Ultravid 7x42 and found the Leicas markedly better in terms of contrast and brightness than the Nikon SEs? The Norwegian site kikkertspesialisten have tested both the Leica Ultravid 7x42s and Zeiss 7x42s, where Leica got higher score for both sharpness, contrast and brightness: http://www.kikkertspesialisten.no/pdf/test7x.pdf

This should indicate that Leica Ultravid 7x42 would be even more superior than the SEs in low-light.

[scampo]

I was looking through a pair of Nikon 8x42HGs this morning and was astonished at just how bright and utterly faithful a view they provided: an extension of your own vision, it seemed. I felt that the view was even a shade better (crisper, more lifelike and restful) than my own Swaro 8.5x42ELs. However, my brother, using my Swaros, felt they had a "bit more edge"; but - what he didn't realise was the Swaros offer a touch more magnification. This had fooled his senses and swayed his opinion wrongly as he later agreed.

I feel you are falling into a similar trap: one of forgetting or dismissing the obvious - that you are not comparing like with like. The next trap is to develop a conclusion based on these false observations - one that has nothing whatever to do with the binoculars concerned.

To put a 7x42 binocular (any good make) against an 8x32 binocular (any good make) and then to conclude that the less bright image provided by the 8x32 means it is a less worthy binocular is, to be kind, an odd conclusion to reach.

The Nikon 8x32SE is regarded by many folk as being amongst the very best in its class.

[marcus]

Gunvald, I sure wish that site was in English. What can you get me?
marcus

[gunvald]

Hi Scampo,

No I am not trying to compare apples with oranges.

I just expected to see a little more contrast in the SEs given their reputation. I also expected a little more visible difference in magnification between the two, so that I would see a loss of magnification in the Zeiss 7x42s but on the other hand, this would then be outweighed by a greater brightness. Perhaps I see what has been discussed earlier, that porro prism binos seems to magnify less than roof prism binos of the same nominal magnification. In this case, the Zeiss 7x42s give almost the same sense of presence as the SEs.

Thus my conclusion that a 7x roof prism might be comparable to a porro 8x.

[Leif]

Hi Scampo,

No I am not trying to compare apples with oranges.

I just expected to see a little more contrast in the SEs given their reputation. I also expected a little more visible difference in magnification between the two, so that I would see a loss of magnification in the Zeiss 7x42s but on the other hand, this would then be outweighed by a greater brightness. Perhaps I see what has been discussed earlier, that porro prism binos seems to magnify less than roof prism binos of the same nominal magnification. In this case, the Zeiss 7x42s give almost the same sense of presence as the SEs.

Thus my conclusion that a 7x roof prism might be comparable to a porro 8x.

The 7x will be brighter due to lower magnification. Why not try using a resolution chart to determine sharpness? In the absence of a resolution chart, a bank note will do. Work out at what distance you can read some of the text with each binocular. The Nikon should win. (I haven't performed the test for myself, so cannot say for sure.) The Nikons compare well with my Swarovski 8.5x42 (as bright, almost as sharp).

I very briefly compared the Zeiss 7x42 BGAT to the Swarovski 8.5x42 EL, Leica 8x32 BN and Zeiss 8x40 Victory and was struck in all cases by how much brighter the 7x42 seemed. It was quite phenomenal!

[gunvald]

Yes, 7x will put more light through the exit pupil, that is an advantage. The Zeiss 7x42 also uses very bright prisms as was discussed in another thread. In the light(!) of this, perhaps I do not realise how good the SEs are, even though their apparent magnification for me seem very close to the Zeiss 7x42s.

I have done some simple resolution tests and prefer the Nikons for their sharpness, both for center and edge sharpness. But, just as with camera lenses, sharpness is good, but contrast is equally important.

Leif, do you find me too demanding if I express slight and moderated, but still, doubts about the contrast of the Nikon SEs? If I had experienced the same as Laika who can see most details with his darkest binocular due what has to be excellent contrast, I would have celebrated the whole weekend after getting my hands on a pair of Nikon SEs.

Now, I perhaps should try the 7x Leica Ultravids as well.

The 7x will be brighter due to lower magnification. Why not try using a resolution chart to determine sharpness? In the absence of a resolution chart, a bank note will do. Work out at what distance you can read some of the text with each binocular. The Nikon should win. (I haven't performed the test for myself, so cannot say for sure.) The Nikons compare well with my Swarovski 8.5x42 (as bright, almost as sharp).

I very briefly compared the Zeiss 7x42 BGAT to the Swarovski 8.5x42 EL, Leica 8x32 BN and Zeiss 8x40 Victory and was struck in all cases by how much brighter the 7x42 seemed. It was quite phenomenal!

[Leif]

Leif, do you find me too demanding if I express slight and moderated, but still, doubts about the contrast of the Nikon SEs? If I had experienced the same as Laika who can see most details with his darkest binocular due what has to be excellent contrast, I would have celebrated the whole weekend after getting my hands on a pair of Nikon SEs.

Now, I perhaps should try the 7x Leica Ultravids as well.

Gunvald: I believe that a 7x binocular will be both brighter and more contrasty than an otherwise equivalent 8x one. Look at that Norwegian site and you will see that - in general - contrast increases with aperture and reduces with magnification.

It rather sounds to me as if you prefer a ~7x40 binocular!

I believe that many years ago Leica used to sell lots of 7x42 bins, but now they sell more 8x42 ones. Maybe this is fashion? Having never spent a day using a 7x binocular, I cannot comment, except to say that I much prefer an 8x binocular to a 10x one. You get more DOF, less shake and a wider field.

[gunvald]

It just hit me that one strong reason Laika can see more details with his Leicas compared to his 7x Fujinon is that the Leicas are 10x. Contrast should still be of importance in low-light where the eye resolves less than in stronger light and would be helped by a superior contrast.

Since we are discussing in a thread started by me about the size of the binocular exit pupil and its importance, I can just say I have now seen the Light, even through the 4 mm exit pupil. Just as was pointed out, it seems to be more about viewing comfort.

I am thus a little surprised about the little difference in viewing comfort between the 7x42s and the 8x32s, both are very good with my glasses in day light as well as in low light. I can still imagine that the Zeiss 7x42s would be more useful when a gale wind blows, just as it did at Strathy Point in Scotland when I visited two years ago.

[laika]

It just hit me that one strong reason Laika can see more details with his Leicas compared to his 7x Fujinon is that the Leicas are 10x. Contrast should still be of importance in low-light where the eye resolves less than in stronger light and would be helped by a superior contrast.

Since we are discussing in a thread started by me about the size of the binocular exit pupil and its importance, I can just say I have now seen the Light, even through the 4 mm exit pupil. Just as was pointed out, it seems to be more about viewing comfort.

I am thus a little surprised about the little difference in viewing comfort between the 7x42s and the 8x32s, both are very good with my glasses in day light as well as in low light. I can still imagine that the Zeiss 7x42s would be more useful when a gale wind blows, just as it did at Strathy Point in Scotland when I visited two years ago.

Gunvald when testing my binoculars it was too dark to see colours.I have also tested my binoculars indoors reading letters from www.vision3k.com/images/snellen_chart.gif in daylight of course the Leica is best ,Zeiss next and Fuji last.The reason is of course the magnification.If i turn of all the lights i can still see the 3 biggest letters with the Leica ,only the A with the Fuji and only something black with the Zeiss.Outdoors looking to a black pipe on a black roof i felt Fuji and Zeiss were almost equal.Leica was still the best in details.
Having said that i feel both Zeiss and Fuji are more comfortable to use in dark and dusk and dawn .Perhaps the bigger FOV and the brihgter view(but less details)are the main reasons? And of course the lesser magnification makes a steadier view.
Twilight performance factor for 10x42=20.49, 7x50=18.71, 8X40=17.89
When talking about high class optics perhaps TP is not a stupid idea?

[zurtfox]

Hi Folks,

Well, to add my twopenn’th to the foregoing, I can only say I am 57, have recently had my (blue) eyes tested and measured and found to have 6mm in the opticians semi-dark room. I mention their colour as apparently this is significant - blue eyes allegedly have the ability to expand more than other colours!

Anyway, I have owned a pair of 8x42 Ultravids (now sold) and still own Nikon 8x32 HG, Swarovski 10x50 SLC and Opticron Taiga 8x25. At dusk the difference between the Nikons and Leica is negligible, the sheer brightness of the Nikons, IMHO, compensating for the difference in objective lens size. The Swarovskis are much brighter, but being best suited for use on a tripod, are not competitive. My bench tests confirmed this, but at this level of engineering I suspect it all becomes very subjective, where ergonomics may be the deciding factor. Where the difference really shows markedly is when used on astronomical subjects, such as nebulae, where the size of the objective lens makes all the difference. Now the 10x50s come into their own.

All I can say is that I still get a buzz every time I put the Nikons to my eyes; its all about the way the image just jumps out at me, its difficult to describe, there is just something about them that meets all 'my' requirements. And that, in the end, is what counts.

Chris

[scampo]

What you say about those Nikons is exactly the conversation I was having this morning with a friend who owns them. Put next to my Swaro 8.5ELs they have an edge that cannot easily be defined. If I had known as much about Nikons two years ago as i have learned since, I would have bought them.

[Tero]

Exit pupil not a big deal unless you are wearing glasses. Then eye relief, exit pupil size etc are a big deal. I asked this in a different thread.

I have seen some 25mm binoculars that worrked well with glasses, and it was due to the exit pupil.