Thread: Binoculars
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Old 11-23-2017, 06:43 PM   #97
BrotherDave
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Quote:
Originally Posted by ranger42c View Post
Aside from physical size and weight... another reason 7x50 became a standard of sorts is that the (young) human eyeball pupil maxes out at about 7mm in full drakness... and the ocular lens on 7x50s is... you guessed it 7mm.

That could mean that 7x50s will "gather"more light (allow more light to flow through)... but then all of that can also be affected by lens quality, the quality of the coatings, design (porro or roof prism), eye relief, etc. Comparing equals, 7x50 usually wins (technically) at night. But a high-end 8x42 could well be better than a low-end 7x50.

And then 8x42s usually don't weigh as much, aren't as bulky, etc.

-Chris
It sounds like you are referencing exit pupil which is really the point when discussing the amount of light which reaches your eye through a pair of binoculars. Exit pupil is calculated by objective lens / ocular lens measurements, thus your example of 7x50 = 7.1mm exit pupil. 8x42 has an exit pupil of 5.25mm, much smaller than 7x50, which can make a huge difference...only if the person's eyes are capable of making use of the extra light.

A healthy (and likely young) human eye pupil can dilate to 7mm or higher but as we age that changes. If you eye can only dilate to 5mm you won't notice the difference in 'brightness' between the two.

It's not just the size of the ocular lens that is at the heart of the issue.
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