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4/22/2019 5:32:20 PM
Posted: 11/24/2014 9:08:52 PM EDT
Hello all, I've been reading up around here for a while now but haven't seen a lot of info about how optics perform in lowlight conditions. I'm currently looking for something to top my 16" BCM carbine, and as indicated, would like good lowlight performance for hunting wolves. I've narrowed it down to a TA33, TA11, or a 1-4x, probably Nightforce but I'm very open to suggestions. Based solely on specs I would assume the TA11 probably collects the most light but I would love to hear how it stacks up against the other two. I'm willing to pay for quality but my budget is limited so I'd like to keep it within a few hundred dollars of 1k on the high end. Any and all input is welcome, especially thoughts on other 1-4x optics. This is a kind of "do it all" rifle so lightweight and close range performance are also important but lowlight is my priority.
Link Posted: 11/24/2014 11:46:07 PM EDT
[Last Edit: 11/25/2014 12:15:55 AM EDT by MS556]
For best low light performance you need good glass, large exit pupil and very easy to see aiming point. Magnification depends on target size and distance. Usually this means 50mm objectives, exit pupil of at least 5mm, preferably 6mm or even a bit more, and a German #4 thick reticle or illuminated dot. As a matter of pure optical science, the larger the objective lens, the more light enters the optics and the more magnification you can use with optimal image brightness. In Europe where game can be legally hunted after dark there is a reason 50 and 56mm objective lens are commonly used. Such scopes are big and heavy however, but can be lighter if magnification is limited to 7 to 9x on the top end.

For instance, a 2-7x36mm scope with good glass will gather a lot more light than any 4x or 1-4x you are considering. A 36mm objective lens at the same 4x has an exit pupil of a whopping 9mm compared to 5 or 6mm for the 1-4x. This lets you go up to a full 7x and still have a 6mm exit pupil. This really matters in low light. If low light hunting performance at distance is your first criteria, you need a larger objective and more than 4x.

How far away will your most distant target be? This will determine max magnification and optimal exit pupil. Then you will have other choices, provided you have good glass.
Link Posted: 11/25/2014 12:50:40 AM EDT
Thank you for responding, I appreciate the input. Max range I think would be 200 yards at most, most common is around 100 though. Clear weather usually allows a considerable amount of light through, especially with snow on the ground, but even then, most the optics I have handled in these conditions struggle to provide a clear picture past 100 yards. I'm hoping to find out if better glass can solve this problem for me. My other concern is that I do use this rifle for other things as well, I have shot in close range action shooting type competitions before and although I do so rarely, I would love to retain the option, thus the acogs and 1-4x's. If a higher power scope would offer that much better vision then I would certainly consider it. Do you have any specific recommendations in this range?
Link Posted: 11/25/2014 1:17:40 AM EDT
Take a look at Elcan. I chose the OS4 for its low light capabilities and eyebox. After years of experience with ACOGs, I was amazed at the light gathering ability of the Elcan.

Good luck with your decision.
Fatkid
Link Posted: 11/25/2014 10:47:11 AM EDT
[Last Edit: 11/25/2014 10:48:10 AM EDT by Chrome308]
For maximum brightness you'll need an objective diameter at least 5 to 7 times your scope's magnification. Anything more is wasted and younger eyes (7mm) can use more than older eyes (which would be closer to the 5x number).

So a 1-4x24 has 6mm exit pupil on 4x which is middle of the road. A young person might be able to see more with a scope with a bit more objective lens size, but an older person with less flexible iris will be getting the most light their eye can get. Dialing that same scope back to 3x would give you an exit pupil of 8mm which is enough for all but the best eyes.

The TA33 (3x33) has 10mm exit pupil so its pretty good and should deliver as much light as your eye can take. Same with the TA11 (3.5x35).

Keep in mind that having a larger objective wont help if your eye only opens to 5mm, a 2-7x56 wont do anything for you as far as light transmission goes. Even tho the scope would be putting out 8mm of light your eye can only take 5mm of it (in this contrived example). This is why we dont see many low power variable scopes from manufacturers with very large objective lenses. They would only cost and weigh more with no tangible benefits.
Link Posted: 11/25/2014 10:53:07 AM EDT
[Last Edit: 11/25/2014 11:06:20 AM EDT by jukeboxx13]
Bigger FOV also equals more light and the higher you go up in magnification the less the FOV which is why you'll need a 50 mm objective.

IMO the TA11 and Nightforce 1-4 is all you'll need for low light at 200 yards after sun down, or at least all I need.

Gluck

ETA: I have looked through a Burris Fullfield 2-7X35, Vortex Viper PST 1-4x24, and an Eotech G33 at parked cars at the dead of night under a dim street light with no issues at 150 yards. I had the best experience with the G33 since the FOV is the biggest at 3x out of the 3 to my eyes, and I also looked through a TA34 but not that far and it performed very well too.
Link Posted: 11/26/2014 2:04:07 AM EDT
Thank you for the responses, I appreciate the input. Regarding the exit pupil, I was always under the impression that this is a measure of the "eyebox", and that anything larger than a human pupil is in a way wasted light (for the purpose of lowlight transmission) as it is not hitting the photo receptors in your retina. Is this a fair statement or am I looking for an optic with a large exit pupil? Also, the TA33 appeals to me more based on size and weight, I'm willing to jump up to the TA11 if it functions better in low light but from what your saying it sounds like the difference is negligible. If this is the case then what exactly is the appeal of the TA11? Just the larger field of view? I've looked through a TA11 and owned a TA31 for a few years but unfortunately have not been able to handle a TA33 so if someone with some agog experience could direct me I would really appreciate it. Thanks again for the replies!
Link Posted: 11/26/2014 4:31:30 AM EDT
Out of your choices I'd go with the NF fc2, Ive got 2 and they are excellent.
Id also recommend the Vortex 1-6, Ive got one of those and its outstanding.
Link Posted: 11/26/2014 10:05:04 AM EDT
Regarding the exit pupil, I was always under the impression that this is a measure of the "eyebox", and that anything larger than a human pupil is in a way wasted light (for the purpose of lowlight transmission) as it is not hitting the photo receptors in your retina. Is this a fair statement or am I looking for an optic with a large exit pupil?
View Quote


That sounds accurate. Larger exit pupils are wasted as fas as light gathering goes, but a lager eyebox is not a bad thing. Nice to have but not your primary concern as long as its large enough to cover the eyes dark adjusted pupil size.
Link Posted: 11/26/2014 6:58:41 PM EDT
Also keep in mind as you rotate the bell of a variable optic, the obj out shrinks. You get a sweet spot when the diameter of the obj out matches your night adapted pupil. Somewhere around 3.4 x on my Burris mtac gives me a 7 mm exit pupil iirc.
Link Posted: 11/26/2014 7:19:32 PM EDT
[Last Edit: 11/26/2014 7:21:32 PM EDT by MS556]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Knife_Sniper:
Also keep in mind as you rotate the bell of a variable optic, the obj out shrinks. You get a sweet spot when the diameter of the obj out matches your night adapted pupil. Somewhere around 3.4 x on my Burris mtac gives me a 7 mm exit pupil iirc.
View Quote


That is absolutely correct, and is the reason why you can get that sweet spot of 7mm optimal exit pupil at higher magnification if you increase objective size. A 40 mm oblective (like a 3-9x) will give you that sweet spot at about 7x, about twice as much effective low light magnification. But if 3.4x is all you need, that's fine. I need more for my purposes.

For most of us, we can't use more than 6mm of exit pupil size, as our pupils will not open up any more than that, so we can twist the magnification ring up a little more before the image starts to dim.
Link Posted: 11/27/2014 12:17:06 AM EDT
Thank you! That last comment really clarified what you were trying to say earlier, for some reason (my ignorance) I just didn't quite grasp it before.
Link Posted: 11/27/2014 3:22:11 AM EDT
Gret thread, great info.


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