Quote:
Originally Posted by RickS
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. |
Quite all right Rick, I thought my explanation sounded a bit dodgy, thanks for the clarification.
Cheers
Chris