Catadioptric lenses used in photography,
are called mirror lenses
They smaller, cheaper and weight much less than a refractive lens with similar long
(usually more than 300mm), but at the sacrifice of some optical concessions.
A mirror optical lens (catadioptric lens) is a lens that has refraction and reflection combined into one optical system, normally obrained by using dioptrics (lenses) and catoptrics (curved mirrors). Combinations of Catadioptrics are employed in focusing systems like headlamps, search lights, optical telescopes, early lighthouse focusing practices,
telephoto lenses and microscopes. Optical devices that employ lens and mirror systems are also called "catadioptric" like catadioptric sensors. and surveillance systems
A refractive style lens with a focal length higher than 300mm may possibly employ up tp twenty optical elements all in one case with a length analogous to the focal distance. A Catadioptric design folds the optical path, significantly decreasing the lens's size and weight, and allowing longer focal lengths similar to 500mm and 1000mm to be more easily available. Whats more,
chromatic aberration, a chief issue with a long refractive lens, is nearly eliminated.
Bower 500mm f/8.0 Manual Focus Telephoto T-Mount Lens Top View
Although catadioptric lenses do contain several shortcomings and they use cannot control light transmission by using a
diaphragm that's adjustable due to the reality that they contain a central impediment. As the lens's
aperture number is preset to the total focal quotient of the total optical system (most usually f/8 of f/11for 500mm designs). Their intonation relay function display low contrast at short spatial frequencies. This folded optical path reduces the lens's length, but also increases its girth.
Their most prominent feature is the annular profile of defocused portions of the photo, transfer a doughnut-shaped bokeh or iris blur, caused by the configuration of the point on the optical axis.
Presently Sony (formerly Minolta) is the only company to offer a 500mm catadioptric lens designed for their line of Alpha cameras. Samyang offers a variety of uniquely priced optics, delivering a lot of optical capability for very little money. These rebranded catadioptric lenses are available under the names of Bower, Opteka, Phoenix, Rokinon, Sakar, Vivitar and others.
Jan 29, 2011