Abstract: An operating knob (20) for an optical system (100) is disclosed. The operating knob (20) has a first and a second coaxially arranged rotating element (21, 22). The first and the second rotating element (21, 22) have at least partly conical form. The first rotating element (21) has at the side directly opposing the second rotating element (22) a larger diameter than the second rotating element (22) and a step is formed at the side of the second rotating element (22) directly opposing the first rotating element (21), wherein the step possesses a diameter which is approximately the diameter of the first rotating element.