Quote:
Originally Posted by Screwdriverone
Oh, and by the way, dont go overboard with the magnification, it was explained to me that the exit pupil on my 11x70mm is around 7mm which is optimal for how far the human pupil can expand at night (gets smaller with age) so if you get a 15 x 70 the extra mag may become wasted as you wont be able to take in all the view anyway as you get older. (someone will no doubt either correct me here or explain it better)
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Not quite right, sorry Chris
The size of the exit pupil is the aperture divided by the magnification. For example, the size of the exit pupil for 10x70 binocs is 7mm and for 20x70 binocs it would be 3.5mm.
A good (young) eye nominally has a maximum pupil size of 7mm when dark adapted. With older eyes or a less dark observing site your pupil size will be less than 7mm. If your pupil is smaller than the exit pupil of the binocs, then the extra light won't reach your retina, so it's actually aperture that's being wasted.
So... unless you have great eyes and a very dark site a pair of 10x50 binocs will be about as effective as a pair of 10x70s.
Cheers,
Rick.