40mm vs 50mm for night hunting

DiRTY DOG

Well-known member
Is the additional size/weight of a 50mm scope worth it vs 40mm for a day/night calling gun? I've never looked thru both side by side at night, local stores don't carry both. Trying to decide on a VX-3i 3.5-10 scope for 50/50 day/night hunting over a spotlight on a 20" AR 15.
 
Being able to see in low light has to do with the size of the exit pupil. This is figured by dividing the objective lens size by the magnification power. For example if you have a 3.5-10x40 scope on 3.5 power it would be 40/3.5=11.42 or 11.42 exit pupil. The higher the exit pupil size the better it will perform in low light. If you have the scope on 10 power it would be 40/10=4.00 or 4.00 exit pupil. Now there are other variables but just remember you get what you pay for in scopes. An $80 scope may look bright in mid day but it will fail in low light due to poor lens quality and poor lens coatings. The VX3i is an excellent scope and will do great at night with either a 40 or 50mm objective.
 
One more thing to consider is that if you are deciding between the exact same scope with the only difference being the objective lens size, the smaller objective will always have the better image quality with everything else being equal. Larger objectives lenses bend light more aggressively and the image quality suffers if uncorrected.
 
Uh... 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.
 
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.
 
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I've got a scope that has a 42 mm objective and when I used it to hunt at night I quickly found out that the Field of View was much more important to ME than the light quality. Looking though a soda straw at night is not any fun. If you can't obtain the target in the scopes field of view then it won't matter how much light gets thought the scope. And the further away the target is the less light it's going to have on it even if you are using a light at night to spotlight the target.

Remember the light waves have to travel from your light out to the target, bounce off the target and come back into your scope and to your eyeball. So if the target is 100 yards away the light waves have to travel twice that distanced or 200 yards before they can be seen.

I went with a EOTech system with the G33 3x magnifier that can flip to the side or flip into the light path. The Holographic Sight is much easier to use at night than my rifle scope. I can shoot with both eyes open and easily get the 65 MOA circle on the target even at night.

If you are hunting coyotes at night remember that the don't always just stand there in one position waiting for you to shoot them. They are on the move. And if they are in close to you it may be hard to find them in your scope view.
 
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The other thing to keep in mind is as we age our eyes might not be able to tell the difference between the 2 scopes. It doesn't matter how much more light a scope lets in if you can't see it. I'm 54 and my 20 year old sons see much better than me using the same lights and optics.

Taken off a simple google search.........

How Aging Affects Other Eye Structures

While normally we think of aging as it relates to conditions such as presbyopia and cataracts, more subtle changes in our vision and eye structures also take place as we grow older. These changes include:

Reduced pupil size. As we age, muscles that control our pupil size and reaction to light lose some strength. This causes the pupil to become smaller and less responsive to changes in ambient lighting.

Because of these changes, people in their 60s need three times more ambient light for comfortable reading than those in their 20s.

 
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I'm 57 and do some night hunting with an Elusive Wildlife Technologies XLR 250. I use three different scopes with objectives of 32, 33 and 44mm. With the spotlight I haven't noticed a difference. Without the spotlight I see better through the scope with a 44mm objective. I attribute that to the glass more than the objective. It is a Meopta while the scope with a 32mm is a VX-3 and 33mm is a VX-R.
 
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