Daytime benefit of large objectives? (1 Viewer)

Do larger objectives offer the benefits in daytime viewing that some claim they do, i.e.:

Some give plausible-sounding reasons for this; others claim it's impossible in principle simply because pupil size limits effective aperture. Technical arguments in past threads I've found sound messy and inconclusive. Some suggest that the central portion of the image circle is still of higher quality than the outer, which again sounds plausible.

But the simpler question is the empirical one: do people actually see these effects or not? If they do, an explanation must be found. If they don't, why do they think they do?

I don't have the right binos available to settle this for myself, and may have been misled in the past by comparing silver mirrors to dielectric, or SP to AK prisms.

So would you settle this with the same model of a quality binocular in different size objective lenses?

An individuals vision would account for differences in opinion. What difference in aperture are we thinking about.

A.W.

Resolution.

Tenex,

There are a number of reasons why a larger objective binocular might deliver a superior image, but not higher effective resolution, brighter shadows and colour detail. As I mentioned in another thread, in bright conditions the iris of the eye progressively blocks the outside of the exit pupil and therefore the corresponding area of the objective. An 8x58 is an 8x16 in bright conditions, as far as your retinal is concerned. The effective resolution will be determined by just 16mm of the objective. Brightness in shadows and colour detail by the transmission profile. Of course shadows can be large enough and deep enough for the eye to need a larger exit pupil.

I known Henry chooses to use a larger exit pupi binocular (8×56?). If a remember correctly it was not because it was a good 8x56, but because it was an excellent 8x40 and smaller when stopped down by the eye.

You can check this out for yourself by taking a large objective binocular an masking the objectives to different diameters. Just a cautionary note. I've found that stopping down an objective will often improve contrast and perceived sharpness but cutting out stray light. I've seen this at all price points.

I can assure you that you can find an effective resolution in a $200 8x32 to match a $2000+ 8x56, but so far I've seen not the quality of coatings for comparable shadow brightness or colour detail.

David

If your optics are diffraction-limited, a larger objective should yield more resolution.

Here's a review I wrote when I bought my 8x56 FL back in 2007:

https://www.birdforum.net/showpost.php?p=840895&postcount=1

I would put things a little differently now, but the basic points about large exit pupil binoculars having lower effective aberrations when combined with a small eye pupil in daylight would remain the same. I still use the big FL as my main birding binocular because no smaller binocular (8x30-42) I've tried since equals its image quality in daylight. I would add that not every large exit pupil binocular lives up to its low aberration potential, something I discovered when I tried to replace the 8x56 FL with an 8x54 HT.

I haven't read Henry's link, but a larger objective means a longer focal length objective.

An 8x56mm objectives may have focal lengths of 200mm or a bit more.
If stopped to 20mm this is f/10 or f/11.
Of course it performs better, although much heavier than a smaller binocular assuming reasonable quality.

fazalmajid said:

If your optics are diffraction-limited, a larger objective should yield more resolution.

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It should reveal more resolution, anyway. BUT, if you know of a diffraction limited BINOCULAR, please let me know what it is. I don't think the big three ever made one. Even so, a lower power binocular need not be diffraction limited to provide excellent images.:eek!::cat:

Bill

fazalmajid said:

If your optics are diffraction-limited, a larger objective should yield more resolution.

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You are referring to the instrument resolution. If you use 116/D as the potential diffraction limit, then an 8x56 could conceivably deliver a 2.1 arcsecond resolution. Binoculars are never that good. The ISO standards committee, which includes representatives from the major optics companies, have decided that an 8x56 only needs to be achieve 7 arcseconds, or three time worse, to meet their standard for high quality binoculars. That would be abysmal if it actually mattered much. When it's dark enough for a 7mm pupil, your acuity is pretty abysmal too.

What really matters is the optical performance when your visual acuity is at it's peak. That would typically be when yout pupil is about 2.5mm, which would correspond to 20mm at the objective for an 8x. Fortunately, a good proportion of binoculars improve comparatively as they are stopped down by the iris, but I've found that the original objective diameter is a poor predictor of the effective resolution. The Zeiss HT 8x54 that Henry mention was a particularly poor example and the Fuji version of the Sightron BSII 8x32 I tested was exceptionally good.

David

Here is my take on bigger apertures. There may be slight optical advantages but they are NOT worth carrying a big binocular for. I once had a Fujinon 7x50 fmtr-sx and Swarovski Habicht 8x30 W at the same time. Comparing them under different lighting conditions I couldn't believe how LITTLE difference there was between them. I also tried Henry's Zeiss 8x56 FL and compared it to some of my other alpha level 32mm and 42mm binoculars. Take my word for it. It is NOT worth carrying a 56mm binocular birding for a better view of the bird if you are walking or hiking. If you are in a stand where you are not hiking much you might use a bigger aperture. For birding stick with a 30, 32 or 42mm binocular. You are not going to miss much by not carrying a 50mm or 56mm binocular and your back and arms will be a lot happier. I use my Canon 10x42 IS-L when I am not hiking a lot because it has IS.

"Here is my take on bigger apertures. There may be slight optical advantages but they are NOT worth carrying a big binocular for. I once had a Fujinon 7x50 fmtr-sx and Swarovski Habicht 8x30 W at the same time. Comparing them under different lighting conditions I couldn't believe how LITTLE difference there was between them. I also tried Henry's Zeiss 8x56 FL and compared it to some of my other alpha level 32mm and 42mm binoculars. Take my word for it. It is NOT worth carrying a 56mm binocular birding for a better view of the bird if you are walking or hiking. If you are in a stand where you are not hiking much you might use a bigger aperture. For birding stick with a 30, 32 or 42mm binocular. You are not going to miss much by not carrying a 50mm or 56mm binocular and your back and arms will be a lot happier. I use my Canon 10x42 IS-L when I am not hiking a lot because it has IS."

Not everyone will notice the difference, but I find the improvement in image quality and viewing comfort with the 8x56 FL to be more than slight compared to any 42mm or especially to any 30-32mm binocular known to me. With the right harness I'm good to go for any distance.

For my priorities the only two current binoculars that might be worth a look as possible replacements are the Swarovski 8x56 SLC and one smaller binocular, the Leica 8x42 Noctivid, which from what I've heard could have the unusually low aberrations I'm looking for.

Larger exit pupils from large objectives also makes it more comfortable to look through, you dont have to keep your head or binocular hold as still.

To my eyes during the day none of my 10X42s match the view through the Ultravid HD+ 10X50, that includes the EDG 10x42.

A.W.

I've got a Swarovski 8x50B and I compared them to a Kowa 8x33 Genesis today (mostly sunny) and I couldn't see any real detail difference. Both were equally spectacular.

As a followup, I agree with Dennis as I would not like carrying the 10X50 all day in the field, it is heavy. The EDG handles like a 8X42 so if pressed to hike I am taking the EDGs not the leicas. The views however during the day with a large apparent FOV and 6.7 degrees actual FOV for a 10X50 are impressive. Even though there is some astigmatism at the field edge when viewing stars and soft edges during daylight viewing, the central core of view is very sharp as I am not looking at the edge anyway. My eyes feel more relaxed with the larger aperture, but there are trade offs.

A.W.

black crow said:

I've got a Swarovski 8x50B and I compared them to a Kowa 8x33 Genesis today (mostly sunny) and I couldn't see any real detail difference. Both were equally spectacular.

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Which of the two would you rather carry in the field? If there was a lot more detail seen with a bigger aperture binocular all birders would be carrying them. You don't see many birders carrying Zeiss 8x56 FL's. There is not a big advantage to carrying huge aperture binoculars.

Right, I feel right at home with a 32mm in the field. Those Swarovski's do best on a monopod and weight in at 41 oz. That's why I never took them off my deck until today when I took them to my friends house. Both of them had very good definition although I'm not the best one to make ultimate judgements. I'm just saying neither of us saw a noticeable difference.

black crow: Yes, to address this question in general, it would be a good idea to compare different objective sizes of the same make/design of binocular. (Henry points out that even different models may differ greatly, FL vs HT.)

Maljunolo: Better resolution... is that your conclusion from experience with different size objectives, or a theoretical prediction? (Like fazalmajid's?)

typo suggests that shadow brightness and color detail are more a function of coatings etc than of objective size.

henry reports better overall image quality with at least some larger objectives stopped down in daylight. He and Binastro explain that by reduction of substantial aberrations inherent in binocular designs with short focal lengths. Henry's linked post is excellent.

Thanks. This is coming together more clearly for me now. Years ago I read an essay "Bird-worthy binoculars" on Better View Desired that clearly explained ("explained"?) how larger objectives deliver better resolution by minimizing diffraction effects, and better color detail and brighter shadows by gathering more light energy, and therefore perform better at long distances or in shadow areas, even in daylight. (Pupil size wasn't mentioned in this context, only for dim light.) It all sounded authoritative and experience-based ("larger objectives will pull in detail that simply is not there in smaller glasses" etc) and of course I imagined one would have to be some sort of expert to publish such an essay. I was just offering this wisdom myself to black crow who had asked about objective size. I do resent being deceived, and conned into deceiving others.

I did just get a larger glass myself (56mm vs 32) and will be comparing them with interest, despite the different designs and manufacturers. My first impression is that they deliver a fairly similar (very high) overall quality of view, with a bit less contrast in the 56, perhaps because it's optimized for lower light in some way?

(Dennis, I don't want to get into any argument about what's "worth carrying", which is a subjective judgment. This is purely informational.)

"I did just get a larger glass myself (56mm vs 32) and will be comparing them with interest, despite the different designs and manufacturers. My first impression is that they deliver a fairly similar (very high) overall quality of view, with a bit less contrast in the 56, perhaps because it's optimized for lower light in some way."

I think we will all be interested to hear your findings. This is an interesting subject. Let us know how the 32mm compares to the 56mm. I think that binoculars in the last few years have improved so much with better coatings and glass that aperture size makes less difference in their performance. I have noticed that the smaller 30mm and 32mm binoculars are getting better and better.