An objective adjusting device has a stationary housing, an adjusting ring with an internal thread and a tube, with an external thread, that is guided rectilinearly in an axial direction and carries optical active elements. The adjusting ring is rotatably supported in the housing, and the tube has at least one axially parallel opening with mutually parallel sliding surfaces in which a guide element connected to the housing engages. The guide element is designed as a lug with a sliding head which is adapted in width to the opening and is provided with a slot, of settable slot width, running in a radial direction.