A system tube of an endoscope optical system, designed to contain cylindrical elements of an image guide provided with lenses and to support the elements by tongues cut out of the wall of the system tube and deformed nonelastically. Wherein the tongues are deformed toward the outside and are bent elastically by a holder toward the inside to below the level of the outer surface of the system tube. In a system tube of an endoscope optical system, designed to contain cylindrical elements of an image guide provided with lenses and to support the elements by means of nonelastically deformed tongues cut out of the wall of the system tube, the tongues are deformed toward the outside and are elastically bent by a holder toward the inside to below the level of the outer surface of the system tube.