Introduction and History

There are two planes of focus in the common rifle scope (lensmatic), for the placement of the reticle. They are commonly called the front focal plane and rear focal plane models. One exception is the Shepherd scope, which has both. Artillery rangefinders have always had at least two reticular focal planes, and sometimes three or four. Optical collimating scopes have always had two focal plane reticles, or aiming points. Interferometers need more than one focal plane aiming point to function.

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