The article describes the construction methods of the three-channel optical system with a separate entrance pupils of channels lenses at different arrangements of entrance pupils. The formulas for calculation of pointed optical system parameters are offered. It is concluded that practically the most rational method for constructing a three-channel optical system with separate entrance pupils of channels lenses is the one which has the entrance pupils located in a vertex of equilateral triangle, the entrance pupils touch each other and the optical axes of channels are parallel to an optical axis of the system.