I bought a 3x9x50 Nikon off a buddy that was too good a price to pass up.. All my other scopes are 40mm.. What is the main advantage of the 50mm? More light gathering?, More field of view?? Trying to decided what gun to put it on..
The 50 has more area for the existing light to strike and be gathered into the scope, but, and it is a big but, the quality of the scope internals determine how much of the gathered light actually gets transmitted through to the eye.
However, quality of the scope is going to have a lot to do with light and clarity. I have a 44mm Zeiss Conquest and I'm more and more amazed every time I take it in the woods because of the light it gathers at dark.