Optical transfer function

The optical transfer function (OTF) of an optical system such as a camera, microscope, human eye, or projector is a scale-dependent description of their imaging contrast. Its magnitude is the image contrast of the harmonic intensity pattern, 1 + cos ⁡ ( 2 π ν ⋅ x ) {\displaystyle 1+\cos(2\pi \nu \cdot x)} , as a function of the spatial frequency, ν {\displaystyle \nu } , while its complex argument indicates a phase shift in the periodic pattern.

Source: Wikipedia — Optical transfer function (CC BY-SA 4.0)