Home Forums Hunting & Shooting Hunting Optics 40mm vs. 50mm+ in 8x Binos

Aside from better low light performance, are there any other benefits to a larger exit pupil?

Do the larger objective bins suffer in normal daylight, vs. a bino with an exit pupil of 5mm or less?

RO

Well of course depends on the particulars. For instance, say you are using a bino that isn't so clear toward the edges. With a 50 mm 8x bino the exit pupil is larger than a 40 mm. In daylight your eye may be open only 2.5 mm. Working backwards, you are only using 20mm of the objective. So what you see in daylight might well be a bit better on the center 20mm of a 50mm objective than the center 20mm of a 40mm objective.

The other thing is the 2.5 mm eye opening swimming in the larger exit pupil of the 50mm objective gives more leeway for eye position and still getting a useful image.

Anyway, those two come to mind, and probably wouldn't apply much to top quality optics.

Someone may try and tell you a 50mm will have higher potential resolution than a 40mm. While true in some sense it only happens at higher magnifications. I forget, but in this objective size range we are talking up around 40 or 50x before that effect matters. It makes no difference at only 8x.

Other than the previously mentioned higher comfort level because of the larger exit pupil (ability for your eye to move around the image) I cannot really say much more. I did have a Meopta Meostar 10x50 at the same time as I had the Cabelas Euro 10x42. The 50 mm was brighter and had better contrast in all conditions (even full daylight)plus it was more comfortable to use because of the larger exit pupil. However, it was noticeably larger and heavier.

On the other hand, moving up in objective size can have some negative effects as well. I have seen several 8x50 and 7x50s that had a narrower field of view than their 40 mm counterparts. I am guessing this is the result of some part of the optical design because it seems fairly consistant across the mid-lower magnification range.

Hope this helps somewhat.

Thanks for the replies.

I thought weight/cost would be a reason to go with a 40mm, but most of my critical glassing is done at dawn and dusk, so low light performance is more critical(to me) than FOV. Anyway, I had a choice between the 8x43 and 8x53 HG BR ASPH Minox and went with the 53's.

RO

Measure your pupil size at dusk (when you do this glassing). Photograph yourself with a digital camera (flash on - no red eye - with a rule held to your forehead for calibration).

If it isn't bigger than 4mm you won't gain any light advantage from a bigger exit pupil (but you will gain the "comfort factor").

I've never seen on even the darkest days in the heaviest dark timber the light conditions so bad an 8X42 wouldn't work during shooting hours. On the ragged edge, yes. But work it did.
If you stack identical makes, but different sizes, it often works out that the larger binocular is very slightly sharper.
The big advantage to a larger binopcular over a smaller one is it holds steadier. That's because it's heavier. Worth having just for that. E