Shrinking pupils

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brian livesey
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Shrinking pupils

Post by brian livesey »

As we age, our pupils shrink. Here's a table showing the average shrinkage in millimeters:

Age......... Pupil Size

19........... 7.0 to 8.0

40........... 6.0

65........... 3.7 to 4.8

74........... 3.0 to 3.4

These figures are taken from "Stargazing with Binoculars", jointly authored by Robin Scagell and David Frydman. The figures are important, because there's no point in acquiring a binocular with a bigger exit pupil than our pupillary size, as light will overspill, making the binocular equivalent in performance to a smaller binocular.
Unfortunately, the table doesn't give a pupillary size for those of us over 75. Maybe we should sip on Horlicks and watch TV instead :lol: .
Last edited by brian livesey on Mon Jan 13, 2020 10:49 am, edited 4 times in total.
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David Frydman
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Re: Shrinking pupils

Post by David Frydman »

Actually, it's worth measuring the pupil size at least approximately.

I am off the bottom of scale above, but still have over 5.0mm pupils even in light pollution.

A friend had 7.0mm pupils at age 65.
Another had 3.0mm pupils at age 70.

I think that the smallest pupil size is around 1.5mm, but I cannot remember if the eye specialist said this was considered a medical condition or not.

The two eye pupils may vary, but usually by small amounts.

I normally use an 8.5x44 binocular, and make full use of the 5.2mm exit pupil.

In bright sunshine 2.5mm is normal, and the eye resolves best at about this size.

As we get older there may be many other eye problems.

Regards,
David

brian livesey
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Re: Shrinking pupils

Post by brian livesey »

Thanks David. In my own case, floaters are getting to be a bit of a problem.
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David Frydman
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Re: Shrinking pupils

Post by David Frydman »

Brian, there is a story relating to that table.

My friend, on reviewing the book, said that the table did not meet his results for older observers.
As he is Britain's senior optics lecturer, in the second edition I modified the values for older people slightly.

Then he said later on that I should modify it again.

I said, no, I cannot keep altering the table when you alter your findings.

The truth is that no size fits all, when it comes to human pupil sizes.
It even changes slightly from day to day or hour to hour.
There is pupil bounce on a short time scale also.

Even published values that I find in peer reviewed papers, do not meet all the cases I have met.
When I see nice curves showing pupil size against age, with no explanation of the wide variation, I just wonder about the rest of their paper.

So, the table above is just a guide, and observers should find out there own pupil size.
An optician will give a rough estimate, but it won't be very dark.
Otherwise get a friend to measure it with a ruler in low light and add 10%. Rough, but better than nothing.

Regards,
David

skyhawk
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Re: Shrinking pupils

Post by skyhawk »

How do you measure them other than a compass in thee eye !
Celestron 8" Edge HD Evolution, Esprit 120mm triplet, 72mm APO, Sky Tee 2, 6" reflecting scope, William Optics Binoviewer, Quark Daystar Ha Chromosphere on 72mm ED, LVW8mm eyepiece and Celestron 19mm Axiom, matched W.O 10 and 20mm, and a few others, D4s, D810,

For info, I am Autistic, Aspergers, ADHD, therefore if I come over as a little "short" on occasions it is not intended, thank you

brian livesey
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Re: Shrinking pupils

Post by brian livesey »

I've compared the brightness level between 7X50 bins and 8X40's on the Orion Nebula. The 40mm aperture yielded a brighter image. Of course, we have to take into account qualitative differences between binoculars too.
The binoculars used for the test are old ( but clean ) standard Japanese porro-prism types: Chinon's and Photax-Paragon's.
Allowance has to be made for a number of variables when comparing binoculars, including variations in pupil size, floaters and rapidly changing air clarity between observations. As you point out in your book David, there's more to making comparative binocular observations than meets the eye.
Last edited by brian livesey on Tue Jan 14, 2020 3:36 pm, edited 1 time in total.
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skyhawk
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Re: Shrinking pupils

Post by skyhawk »

It isn't that simple what about coatings on scopes etc
Celestron 8" Edge HD Evolution, Esprit 120mm triplet, 72mm APO, Sky Tee 2, 6" reflecting scope, William Optics Binoviewer, Quark Daystar Ha Chromosphere on 72mm ED, LVW8mm eyepiece and Celestron 19mm Axiom, matched W.O 10 and 20mm, and a few others, D4s, D810,

For info, I am Autistic, Aspergers, ADHD, therefore if I come over as a little "short" on occasions it is not intended, thank you

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