Hello from a new member,
I just bought a Zeiss 8x30 B/GA (on sale) and am very happy with it (though the pouch is silly). Now, I read that its exit pupil (30/8=3.75) is relatively small and that a larger exit pupil, e.g. on an 8 x 42 (=5.25) would offer better performance in low light conditions, but not otherwise. This is supposed to be related to my eyes' pupils, if these have a maximum opening of 5mm (allegedly related to age), then larger than 5mm is of no use. Two things worry me about this:
a) Looking through my small binos the image always appears just as bright as with the naked eye, be it in broad Greek sunlight or at night. (This was not the case with my previous cheap binos.)
b) Why should the pupils of my binos and of my eyes 'match'? After all, I don't put the one on the other (the pupils of the binos are optically produced inside and those of my eyes are at least 1 cm back).
One explanation: The larger binos (e.g. 8 x 42 vs. 8 x 30) are always brighter. However, in daylight conditions, my eyes' pupils close as much as necessary to show an average brightness. At dawn, they open to max and the difference in brightness shows. (This would be like wearing very light sunglasses; you don't notice it during the day, but it gets dark at night.) - If this is true, the maximum opening of my pupils is irrelevant.
However, in low light, my eyes could operate with less opening of the pupils on a larger bino, which would result in a sharper image.
Hoping for enlightenment,
Takis
P.S.: Just saw that http://www.birdforum.net/showthread.php?t=13550 does have something on this, esp. Jonathan on no. 12., who seems to come to the same conclusion. Is this a settled matter and do we agree that the story "large binos for old age are useless" is a myth?
Well, for 10x, I am definitely going to go with 10x42 over 10x30. With 8x, the smaller ones may be OK.