Operation of several types of spatial filters (SF) is analyzed from the viewpoint of unified principles of constructing images of a scattering volume and its transmission through a spatial filter of a lidar. Diaphragms of several shapes and rasters are considered as SF that define the angular field of view of a lidar receiving system. The main characteristics and efficiency criteria for SF are listed. The shape of matching and optimum diaphragms increasing the signal-to-noise ratio is determined. Diaphragms and rasters intended for controlled vignetting of the transmitted radiation flux within a given range are compared. Several types of lidar SF for isolating multiple scattering and other applications are also considered in the paper.