The Minolta/Sony 500mm Reflex lens is the only production mirror lens designed to auto focus with an SLR camera. There are other mirror lenses that can mount onto current mounts such as Canon EF-mount and Nikon F-mount but all of these mirror lenses are manual focus only. Only this lens can have its focus controlled by the camera's autofocus motor in conjunction with TTL autofocus sensing. In terms of the Minolta AF and subsequent Sony α SLR systems, this lens is an anomaly, being the only lens able to auto focus at 8 (with the exception of this lens, all other AF lenses must be 5.6 or larger for AF to function).
The mirror design does not utilize aperture blades, and thus the aperture of the lens is fixed at 8. Exposure may only be controlled by shutter speed, film or sensor sensitivity, or a rear mounted neutral density filter.
By using a mirror design similar to that of a telescope, this lens uses very little glass compared to traditional telephoto lenses and is thus much smaller, lighter, and far less expensive than traditional lenses in the same focal length. However, this and all other mirror lenses can produce an undesirable donut shaped bokeh in the image it produces.