A device is provided for establishing or releasing the coupling between an adjustment ring, which can be rotated on a base element by way of a detent mechanism and is provided with an adjustment shaft for optical elements, and a cylindrical index ring, which is inserted between the adjustment ring and the base element so as to rotate in relation to an index mark provided on the base element, wherein an inwardly directed ring surface is integrally formed on the edge of the index ring pointing toward the adjustment ring, at least one friction element under spring pressure is inserted between the adjustment ring and the ring surface, and the spring pressure can be removed by way of a pressure element inserted into the top face of the adjustment ring or by way of a lever mechanism.