Home Forums Hunting & Shooting Hunting Optics Does your Exit Pupil Diameter in Low Light affect your choice of Binoculars/scopes?

My optometrist just measured my exit pupil diameter at 7mm for both eyes.

I had her do so under low-light conditions (dimly lit room).

I guess I expected them to be smaller and I'm now considering what advantage that might bring in the field.

That said, how much benefit/advantage would you expect in terms of longer shooting/scouting light, IF WEIGHT IS NOT A FACTOR, between:
1. A quality pair of binos like the Leica 8x32 Ultravid HDs and one that might better optimize my exit pupil 8x42 or x56 ?
2. A quality scope like a Leupold/Zeiss 2.5x8x32 or x36 and a x44 or x56?

I'm looking for input that balances the math with real world experience. I know it's not a practical question necessarily (given added weight of bino/scope with larger objectives) but I'm just curious.

I'll have to do some testing in low light at the next Cabelas I go to!

Does your Exit Pupil Diameter in Low Light affect your choice of Binoculars/scopes?

Thanks,
CL

Yes and no to your last question. I make my decision on binoculars based on personal experience with various past models and configurations. Obviously, some of this experience is going to be influenced by the size of my exit pupil. So, I guess you could say that I do not consciously use this factor in making a determination but subconsciously it probably plays a significant part.

Now, from a hypothetical standpoint a larger exit pupil binocular should provide better low light performance assuming the quality level is maintained from one configuration to the next. With that thought in mind choosing a binocular with a 5, 6 or 7 mm exit pupil would certainly be better than that with one that has just 4 mm.

This is a case of diminishing returns though and a few issues come to mind. For one, size...excluding weight....many oversized binoculars are significantly larger than their 42 or 32 mm counterparts. Second, actual performance differences in the field are going to be slight, again assuming a comparison between products in the same product line. You might see a significant difference between an 8x32 and an 8x56 but that difference is going to be lessened when comparing an 8x32 to an 8x42 or an 8x42 to an 8x56. Third, considering the quality of glass and coatings as well as the sophistication of the high end optical designs, most smaller configurations (8x32 for example) will perform well enough at most distances until the end of legal shooting time (in most states).

Having said all that, I will regularly admit to preferring either an 8x42 or 7x42 configuration for my hunting trips. Physically they are the perfect size for my hands and the weight is well within tolerable limits. Optically, I have yet to find a situation where either configuration, in a high end bino, failed me.

I have used smaller exit pupil binoculars in the past (Zeiss Conquest 8x30) for extended periods of time and really did not find many situations where I felt I needed a larger pupil. The exception would be long distance classing. Surprisingly though the limiting factor was not the brightness of the image but rather the comfort factor in being able to move your eye around the exit pupil to scan instead of just moving the binocular itself.

Some years ago I was running one of my periodic optics tests, with a bunch of binoculars lined up on the sill of the living-room picture window and some deer starting to feed in the coulees above the house. Per usual, I had a few other people also testing, since we all see thing slightly differently.

One of these was an older guy, in his 60's, and very knowledgeable about optics. He consistently thought some of the smaller binoculars (mostly 8x32's) were just as bright as some of the larger ones. Together we finally figured out that, of course, his pupils were not expanding as widely as those of the younger testers, and hence his eyes could not take advantage of the larger exit pupils on 8x42's or 8x50's, which we are also testing.

In the years since I have seen this happen again and again. So yes, it makes a difference. Your eyes should be able to take advantage of a 7mm exit pupil.

OP, how old are you? Seriously, I hear that as one ages, the exit pupil shrinks as the pupil does not dilate as much, therefore one does not or rather cannot utilize say a 7mm but perhaps a 5-6mm.

Ever notice younger folks often have large pupils, and I am not talking about after smoking that funny stuff.....

I think we need to establish a number of things in a discussion like this. First, just how much ability is lost as we age is dependent of other things besides exit pupil size. And the fact that one person may have lost some say down to a 5mm exit pupil, others may not be able to see anything at all, say not much more ability than a 2-3mm exit pupil. All that aside, the best information I have is that people in their 40's through their 60's may well have only the ability to use a 4-4.5mm exit pupil. Sort of an average.
Now for a little practical experience here.
The best way to find out, of course, is to go out and do it. OK. I've done it. Here's what I've found. Twlight and night time conditions vary alot. On bright nights, I can tell things like rocks from stumps as far as 75-100 yds. This would be a full moon night and very clear skys in a very open area with my night night vision fully activated. That alone, activating one's night vision, takes any where from 20-40 mins.
On dark nights, however, you have a whole new set of circumstances. I've been out in dark nights, no moon, full cloud cover, and dark timber, where I couldn't see anything much past 5 yds. Couldn't even be sure where I was putting my feet on. Had to move more carefully etc.
So what works ? On the brightest days, and nights, anything, rifle scope or binocular, will work if it has at least a 4mm exit pupil. How far can I see ? Roughly the magnification of the optic over what my eyes can see w/o it.
When twilight comes, all the way to the end of legal shooting time, I can, for instance, leave my 3.5-10X40 rifle scope set on 10X and see well enough to make a shot. But I can only see a little less than 10X as far with my unaided eyes to the degree than my eyes can.
On dark days, again, it's a whole new game. Here my rifle scopes or binoculars need to be turned down to a 5mm exit pupil. I've never seen, even on the darkest days, in the darkest timber where I needed more during twilight. As it gets darker, I need more exit pupil. All the way down to a 7mm exit pupil. Then, as it gets even darker, even though I can still use the optic, I can't see any further, with any degree of detail, than roughly the magnification of the optic. If all I can see anything significant at all is only 5 yds., then my 6X42 rifle scope can't see anything past 30 yds. Maybe even a little less.
So what to select ? Depends on what you want to do and the distances you want to do it. But as far as exit pupil alone as a decision, that's about all I can say. E

I am in my late 60's & my night vision has gone to hell. My eye specialist didn't measure pupil size but it was apparent there was a difference. I now use Zeiss lens in my eye glasses which helped some. I do a good bit of night hunting & fishing & just purchased a night vision monocular. Shows animals quite well. Getting old is a bitch but the alternative is worse.

CL,
Exit pupil does play some role in my binocular choices. However, if I had 7mm pupils in dim light I would examine just how important low light binocular performance was to me. I don't rely a lot on using binoculars in low light, and generally get by pretty well with a 4-5mm exit pupil in my binoculars. If you deem low light performance to be important for the way you use binoculars, then yes, it seems you should have a binocular with a 7 mm exit pupil. That to me, means a 7x42 beacuse 7-8x50-56 glasses are simply too big and heavy to interest me much. However you indicate weight is not a factor. For a 7x42 that means most of your choices are going to be expensive, but then again that is one place where the difference in expensive glass comes to play.

There seems to be a wider range of price ranges and models available in the 8-10x50-56 binoculars than there is with 7x42 glass, so if you don't want to spend a lot of money, your choices are not so limited.

Keep in mind that brightness has a lot to do with how well a binocular transmits the light it can collect rather than strictly the size of the exit pupil. A 8x56 $19.95 Cheap-Mart special has the same exit pupil, twilight factor, brightness, etc as a $1,995.00 state of the art 8x56. Doesn't take a rocket scientist to figure out what will work best. Also a state of the art 5mm exit pupil glass should be at least as bright as a lesser grade 7mm glass. Again, it seems to me to depend on how you use binoculars.

Steve

Very interesting guys and great comments.

I appreciate it.
Cheers,
CL

I'm not sure what my pupils dialate to, but I know I prefer a large exit pupil on scopes and binos, especially in the field. Even with low light performance out of the picture, I prefer a low to mid power and a large exit pupil just for the ease of use. I like a large exit pupil when I shoulder my rifle or put binos to my eyes. Nice easy viewing and not having to hunt for the sweet spot.

I have a 4x40 Nikon Monarch that is one of my favorite scopes...so easy to just shoulder the rifle and shoot. Even with a great fitting rifle and a good cheek weld, a 2-7x32 on 7 power is irritating to me at times.

A little off the low light topic, but if your eyes dialate well you may find the large exit pupil easier to use (as in find the sweet spot) in low light.

JCM

I understand there is something to that. While my own expereinces seem to indicate this, Barsness has said several times an overly large exit pupil aides in seeing fine details and allows the eye to "roam around" inside the exit pupil. In a rifle scope, it allows more side to side leeway. E

No I don't pay attention.


Beware the large pupil for low light vision. It is a mistress that can come back to haunt you. How? Light has a dual nature in that it can travel through space and time in a form of a wave and/or a particle. Really large pupils (like 7mm) have a visually disturbing side affect of diffraction along the pupillary ruff that can distort and cause a bit of ghosting of images and/or halos and star bursts. If your pupil is 7mm and the exit pupil of the optic is 7mm some of this effect will distort the edges of the field of view. If you have a 7 mm pupil and a 6mm exit pupil this effect is in essence removed and the images are clearer all the way out to the edge. A double edged sword still, because if your pupil is 7 mm and the exit pupil is 8mm, you may enhance the edge distortion. For rifle scopes used as aiming devices you are really only paying attention to the center of the view, you won't perceive this effect, but you may for binos. I have always sunscribed to the train of thought that says stop crunching numbers and being overly analytical of optics; instead go out and try every optic in your price range and compare them with your eyes under as realistic conditions as possible. Your visual system and the physcological process of visual perception for YOU will tell you what is best and that is what you should use no matter what name is stamped on it.

ED