ABSTRACT
F-number is a term widely used in optics that often appears in calculations for first-order parameters, diffraction effects, depth of focus, and radiometric energy transfer. Related parameters include the T-number and numerical aperture. The depth of field of a system may or may not be limited by the optical diffraction limit; therefore, a detailed discussion of alternative calculations for this parameter is included. This entry defines and discusses the application of F-number, numerical aperture, depth of focus, and depth of field.
