Home Forums Hunting & Shooting Hunting Optics Low Light Observations

At last unpacked from the Kansas move, and (almost) sane (nevermind), I have setup my very much reduced inventory of guns and glass. All Loopies, and have been doing some side by side careful comparisons at dusk...(pretty late at this latitude). Here goes... Worst, 2.5 Compact, ,1X4 Shotgun + 10 minuts of usable light. About equal 2X7 VX11 and 4X M8 bettering the 1X4 by a few minuts. Best by a good 10-15 minuts over the 4X and 2X7 the 6X42 M-8...no surprises. I thought the 2.5 would equal at least the 1X4. And the 2X7 is not a bad compromise. I do not like to compromise. Maybe this may be useful to somebody somewhere. Bill

Not what I've seen. First of all, none of them quit all together if they are capable of enough exit pupil. Any of those scopes can do that if you select the proper magnification.
What makes the difference is how much magnification each can achieve at the minimum exit pupil size required for the light conditions present. At 4X, for instance, it can only show you something roughly 4X as far as you can see it w/o a scope. A 6X, roughly 6X as far, etc.
The trick I use is to turn the magnification up as far as it will go as it gets darker. If you can't see anything, and that may well happen as it gets really dark, turn the magnifcation down. But only as far as needed.
Where alot of people get led astray is they want the image to be as bright as possible. That occurs at the lowest magnifications because the eye is awash with light. But you can actually see more detail at the highest possible magnifications. Assuming you can anything at all.
The other thing is that if you start at the lowest magnification, you destroy some of your night vision. That can take as long as 30 mins to come back. Always start at the highest magnifications. E

Like Eremicus said, scopes need to be properly adjusted to work their best. If you have sufficient exit pupil a scope, or bino for that matter, will not stop working. Both are passive devices. Your vision, on the other hand, will stop working long before your aiming or sighting device does.

Roy

Seems logical, eye fatigue. In a dark room looking into the edge of the woods, I (thought) could see objects with the 1X4 set on 3X, that I could not be certain of with the 2.5. This is complicated. Same with the 4X and the 2X7 set on 4X....Bill

It is further complicated by the fact that twilight conditions, and especailly night time conditions, vary alot as to how much light is avaiable. I've seen nights where I could see better than 75 yds. And nights where I couldn't see more than 15-20 feet.
If a person is lacking in night vision, which is very common as we age, that is still another factor. E

I think the point here is that the tester used his eyes with whatever limitation for all of the scopes, so at least the eyes wern't a variable, unless he lost night vison by stopping his pupil down by looking through a too bright scope. If a guy wanted to try this informal test at home with his scopes, what would be the most accurate method? If we presume that some scopes are brighter at the same magnification than other scopes due to coatings ect, regardless of exit pupil size, wouldn't this show up as increased effectivness further into twilight? The overall concept seems valid to me.

John, regardless of what lighting conditions exist when someone compares scopes, the relationship between the scopes tested will remain the same. In other words, if you and I test several scopes and we have different vision capabilities due to age and lighting conditions, the differences between the scopes compared will be fairly equal. The short answer to your last question is, yes.

Roy

During daylight, the eye's pupil shrinks to about 2mm. That's because there is plenty of light, etc. But during low light conditions, it dialates to allow more light in an effort to see better. At a certain point, there is shift in the eye's nerve endings ( rods and cones as they are called) to assit further.
The pupil can dialate quickly, but the shift over to night vision takes a while, like 20-30 mins. Perhaps even longer for some. That shift to night vision is what you don't want to spoil. That's why I always start with the scope at maximum magnification if possible. If I can't see anything, I turn the magnification down to where I can. You can go further to say bring back a lost reticle, but you risk loosing your night vision at a certain point.
I don't recall, even on the darkest days, any significant use of my night vision capability during twilight. The most I've ever needed, and not very often, was a 5mm exit pupil. That means I could still use 8X on a 40mm scope. Still, I tend to play it safe.
So.... if hunting during legal hours, I wouldn't worry about my night vision. Or loss there of. Much.
As far as differences because of coatings, that is apparently another tricky subject. Actual differences between fully multicoated scopes only vary a few percentage points. That shouldn't be visible. However shooters do see a difference. Why ? I believe alot of this has to do with eye relief and eye box sizes. With one, the further the ocular is from the eye, the more dim the image. Simple dispersion. With the other, the image is in focus for a greater depth, thus dispersing it's apparent brightness.
The next question would be does this make a difference ? And, if so, how much ?
Well, with any low light situation, there is a limit as to just how far you can see what degree of detail with a given scope set on whatever magnification works best under those light conditions. I'm of the opinion that the scope with a shorter eye relief and a smaller eye box would be able to see the same degree of detail further. But, how much ? I suspect not much. Certainly not enough to make a 40mm scope perform like a 50mm scope. E

E, I totally get what you are talking about with the night vision, I spent almost 20 years at sea delivering relatively small small sailboats and larger power boats across the ocean, 17 trips from as far as Connecticull to Hawaii, guarding my night vision while on watch was critical, and it was amazing how much you could see just by starlight - no moon. But, without getting overly technical, do you think Uncas's method of test is valid? Is it your position that any difference in light gathering between, say six different types of Leupold scopes, would be hard if not impossible to see as extended viewing into twilight?

I like simple test that eliminate as many variables as possible, and to me Uncas seemed to have come up with one.

Great question. I can tell you exactly how much. If the deer you�re looking at (the light source) is 100 yds away and one scope has 1 inch more eye relief than the other, the scope with long eye relief will give a view of it 0.056% less bright; or the short eye relief scope will be 1.00056 times as bright. If you can see a difference between the two, that ain�t it.

Actually, scratch that. I was wrong. My physics is phuzzy. The inverse square law is applicable between the deer and the objective lens. So the answer is zero difference if the scopes� objective lenses were in the same place. Where the exit pupil is focused (eye relief) is irrelevant to actual brightness of the image.

This is a good thread. IMHO it is difficult to really determine which scope is brightest because including the individual's eyes is a must and we're all different. Another factor is every time we use optics in dim light the surrounding lighting won't be the same. It would seem that would affect optics differently too.

JonA,
So your saying something like this
http://www.dvorakinstruments.com/
Something thats keeps stray light out,wont help either?
dave

No, that'll certainly help. Eliminating stray light from that end will improve the image greatly removing distortions, etc, it causes. Basically increasing the signal to noise ratio along with eliminating any other light from entering your eye as well.

That is NOT! the same as simply having your eye a bit closer with shorter eye relief. A large source of stray light entering that end of the scope actually comes from light reflecting off your face itself; moving it a bit closer does no good.

This can be proven to oneself a couple ways. Pointing a scope (one with a large eyebox and pink reticle helps) toward sunset on low power (to have the most eye relief flexibility), move your head forward and backward. It really doesn't change things much. Now, cup your hands around your eye to emulate the above and there's a big change. Better image and pink reticle gone.

To show what light is coming from your face if that sounded funny, try looking with and without a black cloth draped over your head peaking through a hole. Naked face, pink reticle, lousy image. Black cloth, blacker reticle, better image.

The point I was making and that the above tests prove to anybody who cares to do them, is that an inch or so of eye relief doesn't do much. A cardboard tube sure does, but that has nothing to do with eye relief. Two completely different things.

JonA.
My 1985 pre classic 1.5-6x42 S&B has 3.15 of eye relief.My much newer 1.5-6x42 Flash dot has 3.75 of eye relief.To my eyes the flash dot does not give up anything because of a "longer" eye relief.
Thank you for that discription.I never considered
light reflecting off your face though.Makes since.
dave

Dave, I never really gave much weight to the eye relief/light pollution phenomena as well, mostly because no one can say how much of an effect it actually has. I find it difficult to believe that a half an inch of eye relief either way would have any visible difference to the shooter. If we were talking about 3 inches compared to say 4.5-5 inches, I might consider the possibility of it having a visible impact though. I had read about light reflection from the shooters face awhile back and never gave it much thought, although, it certainly makes sense. It would seem to me that if this is a real factor, a shorter eye relief would be more of an issue than a longer one.

Roy

Six different types of any brand of scope would perform differently depending upon the objective sizes and magnifications that those scope can use or produce.
What I don't believe is that there is much difference between fully multicoated scopes of different brands which have the same magnification ranges and objective sizes. Very small difference, yes, probably from things like eye relief and eye box sizes. I've certainly found from my own scopes that those with shorter eye relief and much smaller eye boxes have an edge when it came to resolving a target. I assume this would carry over into low light performance as well. E

What I have found by actually comparing is that there can be a huge difference.

Interesting read.
http://www.schmidtbender.com/whatislight.shtml
And
http://www.schmidtbender.com/lensandcoatings.shtml
Not hard to understand why loopie doesnt measure up.Seems like there having a nice flashlight made for themselves nowadays.
http://www.leupoldmx.com/

dave

Man, I must be on another planet.

I just want to say publicly: Thank you, gentlemen.

Rick