Front-silvered angled mirror that screws on to a standard or tele lens with the 49mm front thread.  The adaptor is  ‘series 7’,  so it will accept other series 7 adaptors with different size threads if required.  The front ‘lens’  is a dummy !   Watch out for vignetting though with a standard lens.  I have often used this kind of accessory on a movie camera for flopping images.