fixed versus changing pupils - an important variable (1 Viewer)

Obviously, binoculars have a fixed pupil. The human pupil is variable. Of what significance is that to the binocular user? I've never paid much attention to this fact until recently when I had my eye dilated to check for diabetic neuropathy,(none present) but since I had read that our iris loses its capacity to open and shut within a certain range as we age, and hence controls the diameter of our pupils, I decided to see if my dilated pupils could make use of a 7x50 binocular at late dusk. I'm 74.

That same day I waited until the sun had set and then began to use the 7x50. And sure enough I could see quite well, even when it was quite dark. The next day I repeated this process. But of course my pupils were now back to normal and the 7x50 didn't reveal the significant detail it had the night before. In fact it was a whole lot less detail.

I'm not sure what my pupils are in darkness, but they sure aren't 7 mm to 9 mm. Which leads me to believe that all that extra diameter of objectives lens and hence weight of binoculars is somewhat unnecessary for a birding binocular. While the 7.1 pupil of the 7x50 is useful in eye placement, I wonder if seniors like me ought to accept the limitations we bring to binoculars, period. John

John Dracon said:

While the 7.1 pupil of the 7x50 is useful in eye placement, I wonder if seniors like me ought to accept the limitations we bring to binoculars, period. John

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John...

I think each of us, no matter our age, have no alternative but to accept the limitations we bring to binoculars. What is wonderful--there are so many binocular designs to accommodate most of our limitations, as well as differences in the light, terrain, and targets we pursue.

Thank you for your insight.

...Bob
Kentucky, USA

John,
Of course a 7x50 helps you see in low light, but the interesting question is, it any better than a more typical size and much nicer to handle birding binocular?

Stargazers like me are pretty much eye-opening aware. Some people aim for a perfect match between binocular exit and eye, but then, the smallest positioning error will result in noticeable field darkening. I think it's best to have the mismatch at least a 1mm, or better, 1.5mm. Then your eye has some wiggle room and the smaller pupil will still remain completely within the larger. If you want the highest surface brightness in the image, the binocular exit should be the larger of the two. At age 74, a 7x42 or maybe even an 8x42 would "probably" satisfy my arbitrary criterion for both maximum brightness and pleasant usability, at a more manageable size and weight than a 7x50.

My eyes will still open a tad more than 6mm, so the fit with 7x50 is close enough that I can't let my gaze wander around too much in the field without the background sky brightness appearing to vary. I look forward to further aging (I am 59), for one thing it will mean I'm still alive, for another, it will make my 7x50 even nicer to use, but only up to a point. Eventually, 7mm exit pupils will become overkill, adding nothing at all. If that happens at the same time that I become too weak or lazy to handle such a large instrument, aging will be graceful indeed.

Thanks for your thoughts, and that observation, John. I am really in favor of more discussions of eyesight and binocular observing among the geriatric crowd. Those are the birding, astronomy, and optics veterans. If they will please keep slamming, and try to stay aware of and on top of the aging process, and share what's happening and how they deal with it, it will help us all to be better observers late in life.
Ron

Thanks for that, John. It´s a point worth bearing in mind when checking specs of new binos now that I´m approaching fifty.