if I remember correctly the brightness factor is the objective diameter divided by the power,and the average human eye can only usefully dilate to approximately 7 mm, even say if it was 8 mm, a 4X 40 scope is still @ 10.The 50mm objective would give you a 7 up to 7 power, so it should be more of a function of needed magnification. I also have eye problems and I have a couple of 4X28 scopes that are quite bright. One of my favorites is an old Bausch & Lomb that has a post-crosshair reticle, which I dont see anymore in any scopes, the +#3 German" (or is it #4??) is the closest now, but that is only on high end stuff. My scopes for handi's are mostly shotgun scopes because mine are either in pistol calibers, or "brush rifle " calibers. I only use a red dot now on very dark days in heavy timber, and under 100yds. Good luck with the 445.
