Аннотация:An analysis is made of the spectral and spatial resolving powers of a quantum photometer, which is an instrument for absolute (free of reference standards) measurement: of the spectral density of the energy brightness of electromagnetic radiation on the basis of three-frequency parametric conversion. General expression are obtained for the frequency and angular intervals, and also for elements of the area of the beam cross-section of over which averaging is carried out in the determination of the spectral density of the brightness. The dependence is determined of the resolving power of a quantum photometer on the characteristics of a parametric converter and of a recording system used in this photometer.