Firstly, it's vital that you understand to be able to determine which kind suits your demands best how a rifle scope functions. Just like telescopes, rifle scopes have an objective lens by which light passes and focuses on a point in the scope. The picture we see is really the quantity of light permitted to cross through the objective lens when looking through a rifle scope.
Source(S): https://saffordsportinggoods.com/category/guns-and-ammo-shooting/optics/
