Mirror lenses are a cheap alternative to traditional lenses.
Mirror lenses or "Catadioptric" give budget minded photographers a cheap telephoto lense option. Most mirror lenses are available in 500mm and 1000mm focal lengths. They are or have been manufactured by Canon, Nikon, Sony, Tamron, Tokina, Olympus, Sigma, Opteka and Ohnar.
Function
Mirror lens are shorter and fatter than traditional lenses. A solid, raised circular housing in the center of the front element holds one of the two mirrors inside the lens. Light entering the lens travels directly to a concave mirror where it is reflected forward to a smaller mirror. The light is then directed through the internal glass elements of the lens to the film plane or digital sensor.
Focusing
Mirror lenses are a throwback to the days of manual photography. Minolta is the only company to have ever manufactured an autofocus mirror lens. The lens now carries the Sony name after Minolta was purchased by Sony.
Aperture
Only one mirror lens has ever been produced with an adjustable aperture. The Ohnar 300mm f5.6 can be set at f5.6, f8, f11 and f16. The adjustment is done through 15 blades and is in full stops only. All other mirror lenses have fixed apertures. They are f6.3 and f8 on the 500mm's and f11 on the 1000mm's.
Pros
Price is certainly most appealing feature of a mirror lens. In 2010 a 500mm f8 mirror lens costs $300 to $400. A 500mm f4.5 traditional lens cost $3,500 to $4,500. The size can be advantage too as a mirror lens can fit comfortably in a shoulder bag.
Cons
It is not reasonable to think that a $300 lens will give you the same results as a $3,500 lens. As the website PhotoZone says of mirror lenses, "they may be good for personal purposes, but most likely, you will not be able to sell such pictures."
Tags: mirror lens, Mirror lenses, 500mm 1000mm, mirror lens, mirror lenses, traditional lenses