Rayleigh criterion

Rayleigh criterion
(Science: microscopy) A criterion chosen by lord Rayleigh to define the limit of resolution of a diffraction-limited optical instrument. It is the condition that arises when the centre of one diffraction pattern is superimposed with the first minimum of another diffraction pattern, produced by a point (or line) source equally bright as the first. For a microscope under this condition, a 26.5% dip in brightness appears between the two maxima, giving rise to the sensation (or probability) of twoness.
See: abbe limit, sparrow limit (of resolution).