Home Forums Hunting & Shooting Hunting Optics 32mm objective vs 40mm objective

I may be sorry I asked this potentially subjective question.....but how much light loss would a person have in going from a 40mm obj to a 32mm obj,(at the same magnification) say in a Vari X3 leupy?

Long

Your question is a little open ended. For example if the "same magnification" was low enough so the exit pupil from both scopes was larger than the iris of your eye would dilate at the time then there would in effect be no loss.

Ok, lets say at a magnification of 6x.

Long

My Conquest 2.5-8x32 smokes my VX-III 4.5-14x40 in brightness. It's not even close.

At 6X the 40mm will have an exit pupil of 6.7mm, the 32mm 5.3

A normal healthy 19 yo male will have an average pupil size of 5.8mm in 15.9 lux ambient illumination.

If they have the same lenses (coating, number of lenses, etc) then the same % of light will pass through both. The only difference will be the size of the stream of light exiting the scope (exit pupil).

At 6x a 32mm objective will have a 5.3333 exit pupil.

At 6x a 40mm objective will have a 6.6666 exit pupil.

Thanks for the info. Looks like I will be switching out scopes.

Long

I stayed quite late at the range last Saturday and I gave my VX-III 1.75-6x32 a spin at the 300 yard line well after the sun was below the equivalent of last legal light come hunting season.

There is a 6" diameter steel gong on the front of the well weathered plywood target board. It is not painted a contrasting color. When to the naked eye the target board was hard to make out against the brush line and the gong was invisible I was able to use the little scope to see and ring the gong at will.

I bought the little scope on a whim for a very good price and it is staying for sure. I'm liking it so much I may add a VX-3 version to the stable.

Exactly.
But, a question that should be addressed by the buyer is, how large do my eye's pupils get at twighlight? If you're a very young person, they will expand to 7mm in near total darkness. But, as we get older, they don't get near that large. So, to complete this, if you eye's pupils only expand to 5 (As an example), you sure don't need a scope that delivers a 6.666 stream of light. I'm 75, and I will say for sure mine don't expand to 6.666 now.

Assuming both are quality scopes it matters little unless you can hunt legally well past dark. Either will work well past legal shooting times in most places.

Kinda like comparing a car that will do 150mph to a car that will do 130mph while driving on a road with a 70mph speed limit.

Actually, it isn't so much "light loss." They'd both transmit virtually the same amount of light.
But the larger objective scope will allow you to use more magnification with the same exit pupil size. When the light gets low enough to not allow maximum magnifications, the one with the most magnification will allow you to see further into the gloom.
May, or may not, make a difference in a field situation. If it does, it will be at the edges of scope performance. E

Guys like you are so funny. The last time I saw something like that on a post, the guy admitted that his Leupold couldn't see .30 caliber bullet holes @ 100 yds. when set at 8X. E

That's a reasonable comparison.

Amen!

I have read somewhere before that a larger objective tends to lead to better resoloution given that all other factors(glass, coatings etc...) are equal. That is why many long range target scopes have large objectives because those guys dont shoot at night. I have bought several scopes lately to compare and resell and I can say that there hasnt been a whole lot of difference brightness wise. The main difference is in the resoloution or contrast of the image against different types of backgrounds. For some reason, the larger the image the brighter the view seems. My favorite scope to look through so far was a Burris Euro Diamond 1.5-6x40. It had a large view that was very comfortable to my eye. I sold it because I didnt like how far apart the heavy posts were in the #4 reticle. I would love that scope in a Heavy plex.