Re: Tubes.........
Tube diameter <span style="font-weight: bold">can</span> have something to do with one or several of the following:
-Adjustment range: more space inside the tube means more room for erector travel
-Field of view on low power in variable scopes ("tunneling effect"): The reticle needs to be of a certain physical size, and in FFP scopes, the reticle sits on the front of the erector inside the tube. This means that FOV on low power (where the whole reticle is visible and not just the center) and the potential for lots of adjustment range are inversely correlated. Eliminating the tunneling effect while maintaining a large adjustment range in a certain tube diameter is one of the bigger challenges for the designer.
-Rigidity: If the wall thickness remains the same, a bigger tube is significantly more rigid.
-There can also be an influence of the size of the internals on the exit pupil, but in any reasonable design, that can be assumed to be kept to a degree where it does not affect image brightness.
Unfortunately it is hard for the customer to tell if and how the manufacturer is making good use of the extra space a bigger tube offers. If the same model is offered in 1" and 30mm for example, it is safe to assume that the optics are the same and there will only be a potential gain in adjustment range and possibly rigidity. The same goes for cases where the manufacturer has used the optics of a hunting scope and just put them in a bigger tube to create a "tactical" scope.
If the scope is designed from the ground up with a bigger tube diameter, it is possible to make it better both optically (while "optically" rather refers to FOV than image brightness) and mechanically in a bigger tube, but again, there is no equation that says bigger=better for all cases. Bigger can simply mean "more canned air", or it can mean "overall optically and mechanically superior design".
