Definition: Rayleigh criterion; resolving power: A criterion for how finely a set of optics may be able to distinguish the location of objects which are near each other. It begins with the assumption that the central ring of one image should fall on the first dark ring of another image; for an objective lens with diameter d and employing light with a wavelength lambda (usually taken to be 560 nm), the resolving power is approximately given by:
- 1.22 x lambda/d