Sidgwick method

To determine the magnitude of comet by using Sidgwick method,  you should observe comet in a focal plane and remember its magnitude and angular size. After it, you should defocus comparison stars up to the such size, which comet coma has. Then, observer should compare the magnitude of comet, he had remembered before, and the magnitude of defocused comparison stars. As usual, it`s necessary to make several attempts to define the magnitude accurately.  We want to notice, that this method can be applied only for well diffused comets with a small condensation (DC<3). At this time, it`s practically impossible to determine  the magnitude of high condensed comets (e.g. Hale Bopp comet) accurately:  in this case, defocused stars have homogenous brightness, when the brightness of observed comets rapidly decreasing from center to edge.  Latin title of this method is “Vsekhsvyatskii-Steavenson-Sidgwick”, or simply “Sidgwick”, or “In-Out method”, the designation of this method is “S”.