The resolving power of optical imaging system refers to the ability to distinguish the details of two similar points or objects. Rayleigh criterion is used for analysis. (Airy spot formula involving circular hole diffraction)

Li Aiban Baidu Encyclopedia

Rayleigh criterion: when the central maximum of diffraction pattern of one object point coincides with the first minimum position of another object point, the two object points can be resolved, and the optical imaging system is in the resolution limit state.

The resolution of a telescope is expressed by the fact that two objects can just distinguish the opening angle of the objective lens, and its resolution is related to the diameter of its objective lens.

The resolving power of the photographic objective is expressed by the number n of resolvable lines per millimeter on the image plane, and its resolving power is related to the relative aperture of the objective.

The resolving power of a microscope is expressed by the distance between two object points in the resolution limit state, and its resolving power is related to the numerical aperture of the objective lens and the irradiation wavelength (the object itself does not emit light).