The optical transfer function is a complex transfer function where the modulus of the function describe the modulation transfer and the argument of the function describe the phase transfer in an optical system, such as a camera, microscope, human eye, or projector, as a function of spatial frequency. It is used by optical engineers and scientists to describe how the optics project light from the object or scene onto a photographic film, detector array, retina, screen or simply the next item in the transmission chain. The function specifies the translation and contrast reduction of a periodic sine pattern after passing through the lens system, as a function of its periodicity and orientation. Formally, the optical transfer function is defined as the Fourier transform of the point spread function, or impulse response of the optics, i.e. the image of a point source. When this image does not change shape upon lateral translation of the point source, the optical transfer function can be used to study the projection of arbitrary objects or scenes onto the detector or film. While figures of merit such as contrast, sensitivity, and resolution give an intuitive indication of performance, the optical transfer function provides a comprehensive and well-defined characterization of optical systems.

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