What is “MTF”?
MTF is an abbreviation for Modulation Transfer Function. It is the normalized spatial frequency response of film or an optical system. The spatial frequency is usually measured in cycles per millimeter. For an ideal lens the MTF would be a constant 1 at all frequencies. For practical lenses, the MTF starts out near 1 and falls off at increasing frequencies. MTFs vary with the aperture, the distance the image region is from the center, the direction of the pattern (along a radius or 90 degrees to that), the color of the light, and the subject distance. Diffraction effects fundamentally limit the MTF of evan an ideal lens to zero at frequencies beyond 1/(lambda*N) cycles per mm, where lambda is the wavelength of the light. For lambda = 555nm, the peak of the eye’s response, this is very close to 1800/N cycles per mm. The MTF of a system is the product of the properly scaled MTFs of each of its components, as long as there are not two consecutive non-diffusing components. (Thus with prope
