Abstract: A device for rapidly changing objectives with threaded fastening on an optical instrument comprises an instrument adaptor which has, at one end, an external thread corresponding to the external thread of the objective, and, at the other end, a bayonet mount for fixably holding a bayonet base, and an objective adaptor which has, at one end, a bayonet base which can be connected to the bayonet mount of the instrument adaptor, and, at the other end, an internal thread corresponding to the internal thread of the optical instrument.