People turn down their scopes too much, they tend to think a giant exit pupil will help.
Anything beyond 7mm is wasted, the outer part of that big shaft of light falls outside of the aperture in the front of your eye. For those of us who are on the top side of fifty that number can very well be smaller than 7.
Example: I often hunt using a Meopta 3-9x42. Set to 3x I'd get a 14mm exit pupil. Awesome, right? Not so actually. Let's say my 55 year old eye might open to 6mm for this discussion. All of the light that fell on the front of the scope got focused into the 14mm beam and the 6mm aperture it's shining on cuts most of it out. To get the correct figure we don't compare diameters, we must compare areas. When that's done we see only about 18% of the light in that beam gets past the front of my eye to shine on my retina where the "seeing action" happens.
So I turn up the scope to 7x. The light falling on the front of the scope is now focused into a 6mm beam, which is also more intense, all of which gets into my eye. A brighter light is shining on my retina. On top of that the deer or whatever looks larger, and larger objects appear brighter to our visual system.
