Abstract: An optical system of an endoscope for investigation and observation of spaces in medicine and engineering. The construction permits the panoramic observation of the internal surface of the space or channel. The endoscope contains a tube in which a lens is installed along the axis of symmetry and coaxial along the entire internal surface of the tube a longitudinal fiber illumination light guide is installed. A lateral observation nozzle is installed on the tube with the possibility of unlimited rotation around the tube. The nozzle is provided with a unit of two reflection prisms, one is meant for lateral observation and the other for lateral illumination. The lateral observation prism is incorporated into the body of the lateral illumination prism. A diaphragm overlapping the face of the lateral observation prism presented to the lens is arranged, on the nozzle.