# 40 mm vs 50 mm scope



## jonnyr7 (Jan 5, 2010)

The guy at the sporting goods store I went to tried telling me that if I buy a 4-16x40 scope the light transmission would be the same as buying a 4-16x50 scope. He also said if you get a 50mm scope you have to mount it higher making it uncomfortable to shoot as you have to have your head raised up when looking down the scope. Any opinions on the matter?


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## Fallguy (Jan 23, 2004)

I was always under the understanding that the bigger objective lens would let in MORE light during low light periods (dawn and dusk). As for the comfort thing, I suppose it depends on your body proportions, and how you shoulder your rifle. Everyone is different.


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## jonnyr7 (Jan 5, 2010)

ya i thought the bigger lens would let in more light also but the guy i talked to mentioned something about the tube only being able to handle so much or something like that. thats the thing i hate about making purchases at those stores is you never really know who you are talking to or what kind of experience they really have


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## lyonch (Feb 26, 2006)

Mine is a 50mm. they tried talking me out of it as well and yeah i had to get new scope rings, but to me i was glad i went that route. It made shooting more comfortable for me as now i dont have to burry my face into the stock to look through the scope.


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## Sasha and Abby (May 11, 2004)

A bigger lens will allow more light. A bigger tube will transmit more light. Mounting a scope another 4 mm higher (1/8") is a non event. All mine are 56mm lens with 30 mm tubes - and yes, you will see better out of them at dark.


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## xdeano (Jan 14, 2005)

ok lets get technical.

A human pupal is 5-7mm in diameter, any larger and we can't use the light any smaller and the it will seem dim.

So the exit pupal of a scope is the objective lense divide by the power.

example:
4-14x50mm scope

50mm/4 = 12.5mm (it's more light than we need, but in low light it's alright). 
50mm/14 = 3.57mm (bad low light, it'll look very crappy)
so with a 50mm objective your best low light max magnification will be in the 7-8x range

40mm/4 =10mm (still good greater than 7mm)
40/14 =2.85mm (everything will start looking like crap again)
on a 40mm objective your best low light max magnification will be in the 5-8x

Anything below the max mag is will still be good, but is more than is needed and goes to waste.

so your optimum will be the best of both worlds. a higher exit pupal with a 30mm tube at the highest magnification.

so this being said a larger diameter objective will give you more light in the end, but the higher off your barrel you get the more uncomfortable it will be and the more correction you'll have to make on scope for elevation.

56/4 = 14mm
56/14 = 4mm
all good, except for the turkey neck.

You'll be ok with a 50mm objective unless you want the scope closer to the barrel. Then you'll have to give up magnification for your center to center, (center of the barrel to the center of the scope)

I hope this helps somewhat. I tend to have a lot of things going through my head at any give moment and things start sounding like a riddle.

xdeano


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## specialpatrolgroup (Jan 16, 2009)

I have a 50mm scope on my .270, my biggest complaint is that even with high rings, there is not much clearance between the scope and the barrel, limiting cover options, I currently just use a rubber bikini cover and it seems to work well, but flip ups will not fit.


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## tka250 (Sep 24, 2009)

The biggest advantage with a bigger lens is the field of view, not the amount of light it lets in.

Unless you are young a 6mm exit pupil is about all your eye can use. A 40 objective will have 6mm or better up to 6.7X. A 50 will be 6mm or better up to 8.3X.


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## kingcanada (Sep 19, 2009)

always go big. coyotes often respond best at the ends of the day: low light. i have often read about exit pupil and not being able to use a bigger exit. but i can see the difference at the low end any how. i screwed up once and looked at he full moon with my nightforce tactical scope. won't do it again. i couldn't see crap out of my right eye for 30 minutes afterward. "burned" (fatigued) the retina. i was as though i looked at the sun or something. that is a 56 mm objective and good glass. no other scope ever passed that much light through. i have looked at the moon with several other scopes. the mounting height is something you get accustomed to quickly.


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## nosib (Dec 4, 2008)

Correct me if I'm wrong but the objective of the lens only effects the FOV (field of view) the size of the tube is what helps allow more light to get transmitted from one objective to the other. So a 30mm tube will be brighter during low light times than the 1" tube. I currently own a Nightforce nxs and love it. Its a 56mm objective and a 30mm tube. The only thing is it's a heavy bugger. The larger the scope the heavier it is.


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## kdog (Mar 13, 2007)

nosib,

I think you are mistaken. The amount of light is determined by the size of the exit pupil, which is determined by the size of the objective divided by the power setting. Most scopes are fine at low power, even with a small objective, but the real difference comes at the higher powers. Refer back to xdeano's post for a better explanation.

A 30mm tube aids in rigidity, and allows for more adjustment with regard to windage and elevation, but really doesn't enter the exit pupil equation.

KD


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## nosib (Dec 4, 2008)

Okay he corrected me I was wrong. :beer:


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## Longshot (Feb 9, 2004)

I prefer the 50mm also. As xdeano mentioned, watch out for the "turkey neck". (I like that term) Either have a stock that fits well with the height of your scope or an addition to create that positive cheek wield. For example I use one of these:

http://www.midwayusa.com/viewproduct/?p ... ber=125776

http://www.midwayusa.com/viewproduct/?p ... ber=180913

http://www.midwayusa.com/viewproduct/?p ... ber=129354

I like the one that has the zippered pocket and ammo loops. You can lay foam under these to adjust the to the height that is most comfortable for you.


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