How can it be??

[Ray B]

Everyone says that the scope reduces the amount of light going through it; which is to say some of the light that goes in the objective is absorbed by the glass or inner parts of the scope so that less light makes it out of the ocular lens for the user to see. this would mean that the amount of light coming from the area that is the field of view of the scope that reached teh users eye would be more than that same amount of light from the field of view going through the scope. So here is the question: How come a person can see more detail and have better clarity when the light is dim by looking through the scope?

 

[Newboomer]

Magnification.

 

[Ray B]

Magnification.

but it happens even on 1x scopes and according to "them" the vision is supposed to get less as the magnification increases.

 

[BRICKBURN]

A LARGER OBJECTIVE LENS MEANS THE SCOPE WILL BE BRIGHTER

Again, this seems like common sense. But the size of the objective lens is directly tied to the magnification range of the scope. Have you ever noticed how lower-magnification scopes usually have a small diameter objective lens, while high-magnification scopes have larger ones? That's because the combination of these specs is what creates the scope's exit pupil size.

The exit pupil is the disc of light that actually hits your eye. This disc needs to be the right size in order to have a bright, clear image all the way through the magnification range. You can visualize this by taking an un-mounted scope, holding it in your hand with the objective lens facing up. Put a white piece of paper on a table below it and shine a flashlight through the scope. Make sure the scope is the same distance away from the paper as it would be from your eye if you were shooting. With the light shining through the scope, you should see a disc of light hit the paper on the other side. Move the scope up and down to see how the disc goes in and out of focus. Adjust the magnification, and you’ll see the disc get bigger and smaller.

There’s also a very ease mathematical formula to figure out what size your exit pupil will be. It’s the diameter of the objective lens divided by the magnification. This will give you the exit pupil diameter in millimeters.


FOR EXAMPLE:

If you have a 1-4x20mm scope that's on 1x, the equation looks like 1/20 = 20mm exit pupil. If it’s on 4x, it would be 4/20 = 5mm exit pupil

Now let’s say you have a 3-18x44mm scope. If it were on 8x, the equation would be 8/44 = 5.5mm exit pupil. Almost the same as if the 1-4x scope was on 4x.

The other thing to consider is how much light your eye can physically use. It actually varies by age. When you’re young and your eyes are fresh and new, your pupils can dilate quite large, maybe to 7 or 8mm’s. But as you age, your eyes age, as well. Your average 35-year-old eye may only be able to dilate to 4 or 5mm’s. So yes, we could definitely create a scope that gives you a 30mm exit pupil, but your body wouldn’t actually be able to absorb all the light.

https://www.leupold.com/leupold-core/core-knowledge/articles/top-5-optics-myths-explained

 

[BRICKBURN]

Light Transmission and Eye Relief

Scopes don't gather light, as most people think, although the term "light gathering ability" has become accepted jargon. Scopes transmit available light through the lenses to your eye, always losing a bit in the process. The best a scope can hope to offer in light transmission is about a theoretical 98%, which only the very finest (read expensive) scopes can hope to approach. Anything above 95% is considered great, and most scopes are around 90%, give or take a bit. You have to take light transmission figures with a grain of salt. Manufacturers measure light transmission differently, sometimes for specific wavelengths to boost their numbers.

The more magnification you have, the less light you get to your eyepiece. The larger the objective lens, the more you get through your eyepiece.

Aged eyes may dilate to only about four millimeters. Younger eyes may open up to seven millimeters and even more. An exit pupil much larger than your eye can use is wasted. Like drinking out of a fire hose.

The small circle of light that appears in the eyepiece when you hold a scope at arm's length is called an exit pupil. Here's an interesting experiment to help explain it. Take a variable scope, put it at its lowest power, and hold it at arms length. See the circle of light in the ocular lens? That is the exit pupil. The diameter of it in millimeters is the exit pupil size. Now turn the scope up to its highest power and try it again. See how much smaller it gets? Imagine if you are using this scope during poor lighting conditions as common in hunting situations, like dawn or dusk. How small and dark will that exit pupil be? How well do you think you'll be able to see through that tiny circle of light?

A formula for exit pupil is as follows: Divide the objective lens size in millimeters by the magnification. Example: if your 3-9X40 scope is set at 3X, 40 divided by 3 equals 13.3 millimeters, which is large enough for almost all low light applications. If your scope is set at 9X, 40 divided by 9 equals 4.44 millimeters. The difference in available light from the larger exit pupil is significant.

The larger the exit pupil, the less critical the position of your head in relation to the scope is, also. The distance that your eye must be to the ocular lens to get a full, clear picture is called eye relief. Lower powered scopes will have a larger range of distance available for a full view. Higher powered scopes are sometimes very critical in relation to the centering of your eye through the middle of the tube, and the distance your eye must be from the ocular lens. Sometimes there is only a half inch closer or farther you may be to see the whole available view.

Proper Eye Relife on a Scope is Very Important
The largest eye relief currently available for a standard riflescope is about four inches. Four inches is great, and offers enough room for the gun to recoil and not hit your face, if you do your job correctly. Most standard riflescopes have between three and three and a half inches. Higher recoiling guns including slug guns require lots of eye relief to prevent "scope eye" or the cut that some people get from the ocular lens of the scope coming back under recoil and cutting a semicircular gash above the shooter's eye. Shotgun, muzzleloader, and dangerous game scopes sometimes have 5 or 6 inches of eye relief to prevent scope eye, but often at the expense of field of view.

IER (Intermediate Eye Relief) scopes, also known as "Scout scopes" are mounted in front of the receiver of a long gun and require around 9-12 inches of eye relief. LER (Long Eye Relief) scopes, also known as "Pistol scopes" used on handguns may have around 16-20 inches of eye relief.

When mounting a scope, it should be at its highest power, and in a position that your head and neck are comfortable. Your head should be positioned on the stock in the position you will be shooting the most. For instance, if you sight in a gun while shooting off a bench rest, your head tends to sneak up on the stock a bit. If this gun is then used for snap shooting for deer in the woods, your eye relief might not be optimal, nor might your sight picture. Always mount your scope so you don't have to move your head for optimal field of view. Move the scope to your eye, not your eye to the scope.

https://www.opticsplanet.com/howto/how-to-choose-a-riflescope-light-transmission-and-eye-relief.html

 

[Standard Velocity]

Everything Brickburn said.

Also, manufacturers use different coatings to give the color rendition they believe will allow the user to see better in low light conditions. If you look through three different brands of scope you’ll see three different color renditions. After exhaustively looking through high quality scopes I discovered I prefer Leupold. Everything looks a little green but darned if animals don’t just pop in contrast.

 

[Opposite Pole]

I believe the colour coatings/glass composition are aimed at increasing contrast in the spectrum visible to the human eye. Increasing contrast increases our ability to see more things given the same amount of light. This is an important consideration in automotive lighting where a light source is tuned to give higher perceived contrast given the same light output.

 

[mark-hunter]

So here is the question: How come a person can see more detail and have better clarity when the light is dim by looking through the scope?

Brickburn explained quite a lot. I would like just to add a point on fixed scopes, and advantages of variable power scopes.

In case of fixed power scopes, they are designed (in most of cases) to give maximum performance to the users with what is available of their glass and front lense diameter.
They can be cheap, or expensive, but they are designed to give most to the user with glass and available magnification to user.

Will give few examples.
Marine binocluar.
Typicially it is 7x50. Magnification is not too strong because ship main engine vibrations may blure the picture at higher magnification for the user on the bridge.
But, when you divide 50 by 7, you get cca 7 mm exit pupil. As average size pupil, for human eye.

For fixed power rifle scopes, then, standard will be:
- 7x50,
- 8x56,
- 6x42, etc...

This is for most of fixed power scopes, but I have seen sometimes some which are not made to this specs.
Knowledgeable buyer should know what he needs, and what to check, of course.
But above scope fixed power specs should give approximate optimum of light transmission with that particular front lenses diameter.

Conveniences of variable power scopes:
As the people, (or eyes) gets older, things change. Then, there comes the conveniences of variable power scopes.

So, if for example I hunt at low light conditions, with variable scope 3-12x56, I do as follows:
I reduce the power of scope down to 8x, which is about theoretical optimum for such a scope. (56/7=8)
Then I take a look trough the scope, and play again with power up/down, fine tuning, to get most clear picture under the prevailing light conditions.

Once I get the best possible picture, I leave it as it is, and wait for game to show in front of my high stand!!!

At noon, it does not matter.
So if I need to zero the scope on the rifle at perfect light conditions, mid day.
I will not bother with 8x power of scope. I will go to full 12x power, to conveniently see bullet holes on paper target - at 100 meters, or 200 meters, depending on how I zero the rifle. High magnification, conveniences at different time of day.