Quote:
Originally Posted by Anthony
It usually isn't, but most people don't hunt at night. Basically, to figure the image size when it reaches your pupil, divide objective lens size by magnification. If that's smaller than your pupil, it means you aren't getting the full light gathering capability of your eye. A full dilated pupil is about 7mm, which is why 7x50 binoculars used to be a standard. On the other hand, pupil size is probably 2.5-3mm in bright light, so even things like 10x25 will not cause you noticeable issues for daylight observations.
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I've more experience with binoculars than riflescopes, which is why I mentioned 10x42. And those
are used for bird watching in the twilight. And having them give -1 compared to 8x42 doesn't seem realistic to me, from my limited experience.
Basically, if 5:1 was a functional breakpoint, I'd expect to see a definite trend for higher ratios than that for any optic which could be used in twilight. But it seems that the trend is instead for 4:1, at minimum, with only optics below that ratio being clearly regarded as unsuitable for lower light conditions.
There is even something called a 'twilight factor' for optics, which is only slightly more complicated to calculate than just the ratio between objective lens and magnification, but which is apparently
better for typical 10x42 binoculars than 8x42.
In any event, modern glass with good coating gives much better low-light performance from the same size and magnification than older or cheaper alternatives. So it's not just the ratio between objective lens and magnification.
So if 1950s vintage binoculars in 10x42 give a -1, modern Zeiss 10x42 probably do not.