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OTF --> optical transfer function

(Science: microscopy) The relationship between the image produced by an optical instrument and the amplitude and phase of a periodic specimen, measured at various spatial frequencies.

The optical transfer function curve, which shows how well contrast is maintained for finer specimen details, is a complex function, of which the real term gives the ratio of amplitudes, and the imaginary term the phase relationships.

When the brightness of the periodic specimen varies as a sine wave, the modulus or absolute value of the optical transfer function becomes the modulation transfer function, when the brightness varies as a square wave, the modulation transfer function is known as a contrast transfer function.

Acronym: OTF