A protection glass adapter for a surgical microscope has a first abutment surface which can be brought into contact with a corresponding second abutment surface of the microscope. The adapter has a guide opening for receiving a main objective. The guide opening is a truncated cone with a central axis. The greater diameter of the truncated cone is formed toward the first abutment surface. A positioning element of the adapter is rigid and arranged on the first abutment surface. The positioning element is received with form-fit engagement in a mating element on the surgical microscope. The adapter has a holding element. A holding force in the form of a magnetic force can be applied by the holding element parallel to the central axis between the adapter and the microscope.
