Heres the simple run down. If you are over 40 your pupil can only dilate to 5mm. Take the diameter of your objective in mm and divide by the power you are using. ( i.e. 40mm divided by 10 power= a 4mm exit pupil) The exit pupil is the amount of light transmitted to your eye.. Do the math on the scopes you are considering for your answer.
The ideal is thought to be 7mm exit pupil+ simply because it gives you a margin of error for poor placement of your eye...
