Ok, so other than quality glass what makes the biggest difference in light gathering? Objective size, 30mm vs 1 inch. Only ask because I'm looking for a lowlight/night time scope and am looking for info. I know leupold even has a 56mm in the vxl line but is field of view the biggest advantage or is it light gathering?
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The biggest factor in light gathering is exit pupil diameter.This is easily determined by dividing objective size by magnification. The old standard for low light binoculars is 8X56, which equals a 7 mm exit pupil diameter. The pupil diameter of a healthy young adult is 7mm, which means he/she can take advantage of a exit pupil diameter of 7mm, anything over that is not usuable.
Magnification also plays a part, a 10 power with an exit pupil of 7 will allow you to discern more in a low light situation than a 7 power with exit pupil of 7. A 30mm tube diameter will also transmit slightly more light than a 1" tube. When looking at low light situations the quality of the lenses becomes even more important. -
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