Some Basic Riflescope Theory
Understanding This Tool Is Important.
One source of irritation for this author is the lack of technical data published for consumers about binoculars, riflescopes and spotting scopes. Whereas the camera bugs are given such information, sporting optics manufacturers rarely do it so their consumers can make informed purchasing decisions.
Some of the data essential to scope design simply not published for public consumption include the following:
Modulation Transfer Function (MTF) determines the contrast ratio, or reproduction sharpness of a lens, called spatial frequency and is measured as MTF.
MTF is an important consideration in lens design, defining the ability of the lens to provide contrast and resolution. Camera makers provide MTF curves that allow the consumer to know what the ability of the lens is, where 1 is considered the highest quality. A lens system is considered to be of very high quality when the contrast curve is above .9, and where the resolution curve is above .6. However, many inexpensive lenses will maintain these MTF numbers at aperture settings at or above F-16. That is, if you want excellent resolution, contrast and depth of field from your $400 lenses, have enough light available to operate at high aperture settings.
Many modern riflescopes have stops built into their mechanisms that prevent the aperture from opening all the way for the same reason that superior MTF curves can be kept high by keeping the F-stop high.
By Jacob Gottfredson
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