@cafemike thats correct. Tube diameter has nothing to do with light gathering, it is determined by the exit pupil diameter (objective dia divided by magnification) and the lens coatings.
this will explain. https://accurateordnance.com/exit-pupil/
Also, regarding parallax. Parallax error is the change in point of impact versus point of aim depending on whether you are “centered” in the scope field of view. This poi error matters at very long range, but is negligible at the ranges being discussed in this thread, which is why I said it makes no sense to avoid a fixed parallax scope for 400yd and closer shooting.
This is totally different than simply image focus, which sounds like what you are referring to. There are plenty of fixed parallax scopes that are visually crisp from bayonet range to infinty.
Yes, many ffp adjustable parallax scopes have really poor depth of focus and require adjusting—but that says nothing about fixed parallax in general. With some fixed parallax scopes, at higher max magnifications the depth of focus can become more critical and/or you can get some image distortion around the outer edge of the fov at very close range. BUT Id say that is an inherent problem with choosing too much magnification, rather than a problem with fixed parallax in general—ime this only happens at max magnification at extremely close range (say 50 yards or less), and imo its just as easy to dial-back magnification as it is to adjust parallax…and more effective because it comes with the added benefit of optimizing your field of view for such close range. All of my personal fixed parallax scopes are visually crisp from close to far at all magnifications though (including both sfp and ffp). I have found this to be pretty universal, so I dont think a fixed parallax scope that doesnt require parallax adjustment to achieve a crisp focus at all ranges is hard to find.
I personally consider adjustable parallax more of a liability than a benefit on a short-range-only scope. If you want or like adjustable, great…just dont think that its somehow necessary for this use.
this will explain. https://accurateordnance.com/exit-pupil/
Also, regarding parallax. Parallax error is the change in point of impact versus point of aim depending on whether you are “centered” in the scope field of view. This poi error matters at very long range, but is negligible at the ranges being discussed in this thread, which is why I said it makes no sense to avoid a fixed parallax scope for 400yd and closer shooting.
This is totally different than simply image focus, which sounds like what you are referring to. There are plenty of fixed parallax scopes that are visually crisp from bayonet range to infinty.
Yes, many ffp adjustable parallax scopes have really poor depth of focus and require adjusting—but that says nothing about fixed parallax in general. With some fixed parallax scopes, at higher max magnifications the depth of focus can become more critical and/or you can get some image distortion around the outer edge of the fov at very close range. BUT Id say that is an inherent problem with choosing too much magnification, rather than a problem with fixed parallax in general—ime this only happens at max magnification at extremely close range (say 50 yards or less), and imo its just as easy to dial-back magnification as it is to adjust parallax…and more effective because it comes with the added benefit of optimizing your field of view for such close range. All of my personal fixed parallax scopes are visually crisp from close to far at all magnifications though (including both sfp and ffp). I have found this to be pretty universal, so I dont think a fixed parallax scope that doesnt require parallax adjustment to achieve a crisp focus at all ranges is hard to find.
I personally consider adjustable parallax more of a liability than a benefit on a short-range-only scope. If you want or like adjustable, great…just dont think that its somehow necessary for this use.