Sorry, but I just couldn't let this thread lie here without correcting and clarifying some things in Red's post.
The human eye has a maximum dialation of around 4.5mm.
Actually, the human eye dilates to an average maximum of 7mm with the maximum attained at about age 30. As we get older, that number does decrease as he said.
A scope has a pupil just like a human eye.
The pupil in the human eye is a physical structure. Scopes do not have pupils. There is what's called the "exit pupil" which describes the image that's projected to a particular point in space behind the scope. Your eye must be positioned at that exact spot in order for you to see the full field-of-view with maximum resolution. The size of this image is calculated by dividing the objective diameter by the power of magnification. Two scopes, say 3-9x40, but with different light transmission qualities due to different lens quality and coatings, will have the same exit pupil size when both are set to the same magnification.
Notwithstanding the effect lens quality and coatings have on light transmission, the larger the exit pupil the brighter the image up to the point where the exit pupil exceeds the size of our own pupil. It is not necessarily true that the extra light provided by a 50mm objective will be wasted. When a typical variable scope with such an objective is set at it's highest power setting, the extra light is mostly usable.
you can only put so much light through a one inch hole. Thats why most of the premier 12+ power 56mm European scopes have 30mm tubes. Sure they allow for greater crosshair movement (internal clicks) but they also allow more light to be passed through them
This is a common misconception. Light doesn't just pass through a hole when it goes through a scope. It's systematically managed by various lenses. When light passes through the objective lens it's bent and concentrated into a smaller bundle. As long as the scope is designed properly and no physical structure inside it encroaches into this bundle of light, then all the light that can be transmitted through a 30mm scope can also be transmitted through a 1" scope. In fact, some 30mm scopes actually utilize internal lenses that are the same size as those that are incorporated into 1" scopes.
European manufacturers adopted a standard scope tube size that's a nice round metric number, 30mm. We adopted a nice round Imperial number, 1 inch. There's no more to it than that.
Larger scope tubes do have a couple of advantages. They're a little more rigid and they offer greater windage and elevation adjustment travel as was stated.
Sorry, just needed to correct some things. BTW, a good scope with a 40mm objective is all that's needed for any big game hunting I can think of in the U.S., so I agree totally with Red on that. My Zeiss Conquest 3-9x40 is my favorite. With it I could hunt past legal shooting hours if I wanted to (I don't). Anyway, I'm out of here for a few days. Happy New Year.