Eye Relief and Light Transmission in a Rifle Scope

riflescope2Most people think that scopes gather light, but the truth is that they transmit available light instead. Most people think that scopes gather light because the term “light gathering ability” is thrown around a lot. Instead, scopes transmit the light that is available through the lens and to your eye, but they always lose a little bit of light in this process. The best that a scope can ever hope to offer when it comes to light transmission is a theoretical 98% meaning that 2% of light is always lost. This is only generally achieved by the absolute finest in scopes, which means the most expensive scopes on the market in most cases. Anything that is above around 95% is considered to be really great. Most scopes on the other hand are going to be closer to around 90%, give or take just a little bit.

Generally, the more magnification that you have, the less light you are going to get for your eyepiece. The larger that your objective lens is, the more you are going to get through the eyepiece.

Aged eyes can dilate only to about 4 mm. Younger eyes may be able to open up to as much as 7 mm or more.

There will be a small circle of light appearing in the eye piece when you hold the scope at arms length, and this is known as the exit pupil. The circle of light that you see in the ocular lens is this exit pupil, and the diameter of this in millimeters is what is known as the pupil size. When you use the scope during a poor lighting condition, you should imagine how small and how dark the exit pupil is going to be when you are choosing a rifle scope. How well are you going to be able to see your target through that tiny little circle of light? Is the amount of light enough to let you take advantage of the scope?

There is a formula to consider for the exit pupil calculation, which is as follows: You should take the objective lens size, convert it into millimeters and divide it by the score magnification. This is the way to figure out how much available light you are going to have, and the difference may be really significant.

The larger that your exit pupil is, the less critical that the position will be for your head in relation to where the scope is. The distance that your eye needs to be to the ocular lens in order to get a clear and full picture is known as eye relief. Scopes with less power will have a larger distance range to obtain a full view, while higher power scopes are typically much more critical when it comes to the centering of the eye through the tube’s middle as well as the required distance from the scope’s ocular lens.

Photo Credits: SamJUK

Originally posted 2009-10-19 03:34:48. Republished by Blog Post Promoter

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