Home Forums Hunting & Shooting Hunting Optics Large Objective scopes and low light shooting

That's easy; FOV is a function of focal length, distance and CoC when the aperture is constant. In an LPVO, the focal length will be quite short and at low magnification, the CoC will be larger so you will have a very large FOV with little magnification. I haven't a clue what the specs of your Leupold LPVO are, but it probably has a low top magnification so the exit pupil will always be a good size. If your LPVO goes to 8X or 10X, you will see a drop off in exit pupil size, but you would probably not be using high magnification at night.

Great info

Actually, that's a common misconception. Most of my moonlight shots are at 8-10x and sometimes higher. You need magnification to discern detail at night. For example, a 150 or 175 yard shot on a hog in daylight is a piece of cake with 3x or 4x. But at night, you'd have an extremely difficult time at those lower magnifications and likely couldn't tell for certain if the animal was broadside, quartering, etc. -- or even if it's a hog at all and not a dog or calf.

With most any amount of moon I can run a Kahles all night...

Exit pupil is equal to the objective diameter divided by magnification on the maximum magnification. It is also often the case in the upper half (approximately) of the magnification range. On the lowest magnification, I am not aware of any currently-made variable riflescope (maybe there some target type ones, but I have not tested those in a while) where the entire objective lens is used on the lowest magnification. For example, taking the Trijicon 2.5-10x56 mentioned earlier in this thread, it has exit pupil of approximately 16mm on 2.5x. That means on low power it only uses about 40 millimeters of a 56mm objective.

As far as how much exit pupil you need for low light use is somewhat individual, but you generally want it to be a bit more than your eye pupil. There are several good reasons for that. I hope Rick does not mind if I post a link to my website, but I did a livestream on that exact topic about a month ago:
https://darklordofoptics.locals.com/post/2946143/exit-pupil-and-how-the-eye-works

I travel a good bit for work and these are the topics that are easy to discuss without props, so I can cover them when I am on the road.

Lastly, when it is truly pitch black, thermal is the way to go. An hour after sunset is doable with some environments with conventional scopes, but that really depends on the terrain, where the moon is and at what phase, the cloud cover, etc. There is a reason why you want an exit pupil larger than your eye pupil in low light.

One of the things that happens is that your visual acuity goes down when the eye pupil dilates, so this is something you want to do some experimentation with. On top of that, your eyes depth of field goes to hell in a handbasket. The way you perceive the reticle, for example, can change substantially, especially if you have not checked eyepiece focus with dilated eye pupil.

ILya

Very good point. I find that etched reticles stand out significantly better in low light than wire reticles.

short answer in short NO. the reality is in low light you have trouble identifying the quality of animal you're shooting at if the distance is very far. if the distance aint that far, say 200 yards. you can simply dial the scope down to 4 or 5x in which case as long as its not a 70's redfield the glass should be decent enough to make the shot.

all the scopes I hunt with are capable of shooting well beyond legal shooting light.

Years ago I lived in the Outer Banks.

I used to take my Jeep out on the beach in the crazy bright summer sun.

My girlfriend was obsessed with blow jobs in public.

I put on her Varnets once (she didn't need them at that moment).

Holy smoke... them durn Europeans sure understand lens and coatings...

I have been a Euro junkie ever since.

ILya,

Thanks for injecting some optical reality into this thread. I had been holding off, mostly because of eventually growing weary of battling optical myths among hunters.

But I also doubt that most following this thread will be able to understand (much less appreciate) your post.

Apparently you are doing well!

Best,
John

Then why are mfgs making 56mm objective scopes????
What’s the market and purpose?

So that you can dial to 5-6x and still have a comfortable ~10mm exit pupil. The smaller the objective, the lower you have to go to maintain the same exit pupil size.

FWIW, yesterday I actually managed to get to and into my stand in very thick brushy cover before legal shooting time, which was 0630. Clear sky, bare trees. Spent some time looking around and checking whether or not I could see well enough to shoot through my scope, a Trijicon Accupoint 3-9x40 with green dot at the center of a duplex, set naturally on 3. I was expecting any deer to come on one of the trails that run from 5-25 yards from the ladder stand, so that’s where I was checking. When at last I was satisfied I could make out a deer within that space well enough to shoot safely and effectively, I checked the time it was 0628. Before that, while I could certainly have made out a deer and identified its sex, detecting obstacles between us might have been dicey. The buck that finally volunteered at 0915 would have been pretty safe at 0630, because he was 50 yards out, facing straight at me in head-high weeds and briars. Even if I had seen him there, not at all certain, determining if the path was clear would have been difficult. Perhaps if I turned up the power a bit I could have made stuff out better in that light, but I might also have lost my opportunity while futzing with the power ring.

One other thing I discovered while peeping through the Accupoint is that at first light, the tritium was providing all the illumination for the dot. I covered the little window with my hand and its brightness didn’t change. It was just bright enough to draw my eye, with no flaring or bleeding over into the other parts of the image. When I took my shot, it was very clear against the deer standing in sunlight. Where it falls short, is when under cover in daylight, as when under a covered shooting bench or in a shooting box or pop-up. The tritium isn’t bright enough to be seen, and the fiber-optic won’t collect enough light either. Those who hunt from such structures and want an illuminated reticle should go with something that uses a battery. For me, the Accupoint does what I need, and is as small and light as other 3-9s.

The riflescopes with 56mm objectives are usually high magnification riflescopes. You need a larger objective to get a usable exit pupil and for the increased image resolution.

For example, my current F-TR competition riflescope is a March-X 10-60X56 HM, which I use at 50X all the time. The exit pupil size is 1.12mm and this means I have to be properly behind this riflescope to see anything. The 56mm objective forms the image at the front of the erector tube with much more resolution than with the same glass in a 40mm, or 36mm, or 24mm objective, at the same focal length. You can go read about Dawes limit, if you want to learn more. The larger the objective, the greater the resolution (with all the applicable caveats). The downside is that the DOF is greatly reduced in a 56mm objective, compared to the 40mm, and smaller.

This scope at 50X provides me the detail that I need for shooting a 1000-yard competition on an NRA LR1FC target where the X-ring is 5 inches across, and I can distinguish each of the rings from the other concentric rings. I used the low power 10X when I first sighted in the riflescope, and I don't think I've ever used at less than 40X at first and then 50X for the last couple of years.

More recently, I have been testing a March-X 8-80X56 HM set at 80X on the same target. The exit pupil is a tiny 0.7mm, but that is not an issue when you are properly behind the riflescope. I have used it at 50X and 60X, but 80X is just too attractive to mess with the lower magnifications.

This is a different world and use from most of the users here. These scopes are much rarer than hunting scopes usually discussed here, but they have their users and that's why some manufacturers produce them.

I will also state that the exit pupil at the low end on these scopes (and probably most scopes with a base magnification greater than 3X) is definitely not what you would expect if you divided the objective by the low magnification. It's smaller, and sometimes a lot smaller.

Thanks, John.

I am doing well, but my life has gotten even busier, so I do not get involved in quite so many battles. If I see an interesting topic, I swing by, say my piece, and move on. I figure if I get enough information out there, eventually there is going to be enough critical mass to make a difference. I do try to check back on the threads where I have commented.

Now that the hunting season is almost over, I will have more time for a bit. I have a few ideas for new videos and articles, some of which will be addressing core understanding issues more so than just product reviews.

ILya

This. I recently shot a hog on a feeder at 50 yards in very low light. Several hogs were jostling each other at the feeder and while I could see all of them at 3x, I couldn't really understand what was going on: which hog was in front of the others, etc. I cranked my Nightforce 3-10x42 SHV up to about 6-7x and was able to see what was important.

Had the hogs been any farther, I would have cranked the scope up even more.


Okie John

Good post and paragraphs.

Thanks for taking to time.

So few actually use an optic in low light.

Magnification increases the "brightness" of the image.

On 10X the hunter is "sort of" 10 times closer.

The best image will be at the max zoom that offers a bigger or equal exit appature to you eyes pupil.

Add in the better resolution of the large objective and a significant gain can be had in low light.

Thanks, Okie John, for some real-world input

Nobody has mentioned lens quality. You can put a paint bucket size objective on a cheap scope and it want make it any better.
My first quality scope was a steel tube Kahles. 3x12-56. Followed by Swaro aluminum tube 3x12-56. For the most part twin brothers. These models preceded the Swaro PH series scopes. They were also the last scopes that lead was used in making the lens. Lens quality dropped because of this.
Basically you get what you pay for. Hasbeen

Image brightness is solely attributed to exit pupil size, up to the point that it matches the size of your own dilated pupil. If the exit pupil is larger than your own pupil, then you have effectively reduced the aperture of your scope. So yeah, in that sense the brightest image will be perceived when the exit pupil matches your own pupil.

But magnification on it’s own does not increase brightness. Only the size.
Although a point source of light won’t lose as much brightness as objects that are absorbing or reflecting light as magnification increases.

Many objects will disappear as magnification increases and the exit pupil gets smaller than your own. But given enough light to illuminate your target, you can perceive a sharper image down to about a 2mm exit pupil. Because this centers the light on the most sensitive part of the eye.
Although with a dilated pupil you may perceive more details with higher magnification, given enough light on the target, the image will begin to blur with an exit pupil much smaller than 2mm.

First up
I am not a Scope Expert.
Or a Firearm Expert.
That Said

I put a March 8 X 80 56mm on my Springfield M21
I took it to the range ( I know Just Paper Targets)
The first time out I was shooting about an half hour after everyone else had packed up.
Even the open sight guys.
I gave up on everything except the March.
This Scope is amazing.
I use the 80 for a spotting scope and dial it back to shoot.
The highest I shoot is at 60 and some time 50.
My Hart beat and breathing make it hard for me to sight anything in with the bouncing Reticle.

I love this Scope and am very happy that I put the money down when I did.
The very first time I took it out I was trying to sight it in at 100 Yards and even Bagged I was loosing the Target.
I was getting Frustrated until I figured out that at 100 yards set at 80 I was looking at the grain structure of the paper Target after I figured it out and had a DU moment sun was going down and I popped off 3 shots that I could cover with w Nickle.
This was after everyone was packing up and getting to dark with open sights.

You get what you pay for some times.