Originally Posted By: VarminterrorUh... Your post makes the case a larger objective is better in low light than a smaller one.
Exit pupil: 40mm at 3.5x = 11.43mm, 50mm at 3.5x = 14.29mm
At the same magnification setting in the same model line with the same transmissivity, 25% more light enters AND exits a 50mm scope than a 40mm. Another way to look at it - for the same light passing through the scope and the same FOV at range, a 50mm can run at higher magnification than a 40, giving you a better view of your target.
In my experience with lenses (be it rifle scopes or other devices), the CENTER of the image doesn't get distorted any greater in a larger objective than in a smaller one. The edge quality will suffer as it's squeezed through the tube (figuratively) more than the edge of the 40mm, but any difference in the center is negligible - more prone to production quality differences and dumb luck than any design issue.
There's no design feature which trumps glass quality, however. The VX-3i isn't bad glass, but I can say there is better out there, even for the same price (or less). I have a great number of scope models, but the 4.5-14x50mm SF 30mm mil-dot is my favored model for hunting, night or day. It's huge, no denying that, but it does what I want it to do.
Your comparing light transmission to image quality. It not the same thing. Call any optics company and ask them this question. If two scopes are identical except for objective size, which one will have better image quality? The smaller objective every time. As far as light transmission, in bright daylight our pupil will probably be around 2-3mm and in twilight it will grow to 4-5mm so the difference between the 40mm and 50mm objective will be minimal.
Also, just because a scope may have a bigger objective does not necessarily mean the scope will have more light transmission. Objectives are not funnels. What goes in does not come out. The number of lenses and the coatings on the lenses determines how much light makes it through to our eye.