Catadioptric lenses in photography. (Mirror lenses)
Mirror lenses are used from the early seventies in camera systems. The lens is more compact then the normal tele lens because the use of the Cassegrain design. This design makes use of mirrors to fold the optical path of the light and reduces the physical length of the lens. By using a convex secondary mirror which multiplies the focal length many times (up to 4 to 5 times). This creates lenses with focal lengths from 250mm to up to 2000mm that are much shorter and compact than their long focus counterparts. Moreover, Chromatic aberration, a major problem with long refractive lenses and off-axis aberration a big problem with reflective telescopes is almost eliminated by the catadioptric system, making it very suitable for 24x36mmphotography.
Several companies made catadioptric lenses: Nikon under the name Reflex Nikkors for the F system, Canon Offered a 500mm F8 and a 1000mm F11 lens for the FD system, Minolta offered a compact 250mm , a 500mm and a 500mm AF lens. Samyang, Vivitar , Yashica and Makinon also made several lenses. The shortest lens was made by Minolta a 250mm F5.6 lens, and Makinon made a 300mm F5.6 lens. The most common focal length is 500mm F8. But Nikon made a 500mm F5 lens. Also, a 500 to 800mm Zoom lens was made by Starblitz.
So many are out there to be found and be used again also on the newer digital cameras.
Shooting digitally gives mirror lenses a new lease of life. One of the characteristics that these lenses have is that they eat contrast. Once in Photoshop/Lightroom etc it is so easy to give contrast a boost.