The resolving power (or resolution) is the ability of an optical system to separate two closely spaced point sources, i.e., resolve detail in an object being imaged at the nominal distance. A resolution test is a visual test of the resolution limit (resolving power) of an imaging optical system. The test is conducted by viewing an illuminated-resolution test pattern comprising groups of black and white bars with 100% contrast.

Each group represents a different spatial frequency in cycles per millimeter (cy/mm). The largest frequency that cannot be resolved defines the resolution limit of the tested system.