Rayleigh criterion

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criterion, Rayleigh 

Observation first made by Rayleigh that the images of two point objects will be resolved when the central maximum in the diffraction pattern of one image coincides with the first minimum of the diffraction pattern of the other image. For a perfect eye, with a 2 mm pupil, this criterion corresponds to a theoretical tolerance in focusing equal to about 0.075 D. See Airy's disc; diffraction; limit of resolution.