was reading an article on scopes defining exit pupil, available light etc. had a thought for somebody in the know. so we mathematically define the amount of light the eye can use. what happens as the eye ages and further when cataracts develop?? would not the whole formula go down the drain??

It is the question WHAT YOUR Eyes could do... My iris opens up to 8mm easily at the moment (age 35 yrs) (just in front of the mirror and not after 1/2 hour of darkness or medical treatment) - so I could use any technical device and use 100% of it theoretically. So check your eyes by an optometrist - anything else would be grey therory!)

Yes the diameter exit pupil is what the best meassurement is for any light gathering scope, BUT see also that the optical quality of your device is more then essential: So is my Swarovski EL 8,5x42 better to use even under lowest light then my Zeiss Classic 8x56: The difference is made by brilliance, sharpness and contrast of the Swarovski - even against the much greater (7mm at the Zeiss while just 5mm at the Swarovski EL) exit pupil of the Zeiss...

So, no rule without exceptions, no comparisson between aple and tears !

What happens if YOUR eye pupil is smaller then the exit pupil of your optical device? -> the image get´s "calmer" and you are not focussed to have it "in the center spot of your eye" - you then have an "Eye motion box" - so comfort is higher while the amount of light in your eye is limited by your iris...

Also something to consider is, the larger the exit pupil of your scope, the less ctitical the exact placement of your eye behind the scope.

This can help when mouting the rifle and shooting rapidly.

There are other factors that those formulas do not cover. A BSA and a Zeiss Conquest, both in 3-9x40, would have the same exit pupil, right? But which would be the better under low-light conditions actually has nothing to do with the exit pupil comparison as one would perform admirably while the other would be miserable at best.

quote:

Originally posted by butchloc:
was reading an article on scopes defining exit pupil, available light etc. had a thought for somebody in the know. so we mathematically define the amount of light the eye can use. what happens as the eye ages and further when cataracts develop?? would not the whole formula go down the drain??

By convention, a scope's exit pupil is calculated by dividing the scope power into the objective size. That has nothing to do with how well your eyes perform. The quality of your eyes is not used in the exit pupil equation.

The exit pupil has to do with the amount of light entering your eye. The objective lense and other aspects of the scope will determine how much light can be brought to focus. Yes, as you age, your pupil will not respond as easily, quickly or as well as it did when you were younger. Anything that affects your vision will affect what you see whether through a scope or naked eye. In that sense, the formula is based on standards so to speak. Anything outside of that standard will change the outcome slightly.

Ken....

As "general statement" as you get older your pupil will not dialate (spelling?) beyond 5 CM. Younger folks typically will have their pupils dialate to 7 CM.
Guys like me @ 52 cannot really utilize more than a 5 CM exite pupil on a scope or bino. Additional exite pupil may assist with the "eye box".
All being equal with the quality of glass, especially in Bino's. Thank god for Leica, Zeiss and Swar.
I asked a eye doctor about this 10 years ago when "I HAD" to get reading glasses. They confirmed what I had previously read.
To me the eye box and eye relief are very important and I am a nut for high quailty glass.

quote:

Originally posted by eezridr:
As "general statement" as you get older your pupil will not dialate (spelling?) beyond 5 CM. Younger folks typically will have their pupils dialate to 7 CM.
Guys like me @ 52 cannot really utilize more than a 5 CM exite pupil on a scope or bino. Additional exite pupil may assist with the "eye box".
All being equal with the quality of glass, especially in Bino's. Thank god for Leica, Zeiss and Swar.
I asked a eye doctor about this 10 years ago when "I HAD" to get reading glasses. They confirmed what I had previously read.
To me the eye box and eye relief are very important and I am a nut for high quailty glass.

I was 42 when my eyes went bad also. It was glasses from then on till two years ago when I had cataract's so bad I could hardly drive a car at night. I had new lenses installed in each eye and I can use iron sights again. And, I'm 100% in agreement with you on the eye box being important. At age 75, my pupils probably don't dialate much at all, so as long as I have a scope that has maybe 4mm exit pupil, or greater, I can get my eye pupil inside the light beam exiting from the scope's ocular lens.
Quality of glass trumps almost everything else.