Originally posted by goosespirit:
Bird dog,
I think (could be wrong) that the light gathering capability is much more of a functioin of the objective size, not the magnification. So, a 6x32 glass will gather more light than a 8x32....Anyone care to chime in,
It's actually a function of a combination of the two. "Light Gathering Ability" is roughly measured by the "exit pupil" which is calculated by dividing the size of the objective lens by the magnification of the optic.
Hence a 10x40 has an EP of 4mm; as does an 8x32. These two glasses would offer roughly the same level of brightness.
A 6x30 glass would have an exit pupil of 5 which is also equivalent to an 8x40 or a 10x50. Thus they would all offer essentially the same level of brightness - and would all be brighter than the above mentioned optics sporting their 4mm EP
Of course, type of glass, build quality,lens coatings (their type, quantity, and quality), degree and quality of internal baffling, and other issues can complicate the matter somewhat but, the exit pupil is definitely the place to start when evaluating the relative brightness of any optic.