Catadioptric system
[1] Léon Foucault developed a catadioptric microscope in 1859 to counteract aberrations of using a lens to image objects at high power.
Their designs can have simple all-spherical surfaces and can take advantage of a folded optical path that reduces the mass of the telescope, making them easier to manufacture.
Many types employ “correctors”, a lens or curved mirror in a combined image-forming optical system so that the reflective or refractive element can correct the aberrations produced by its counterpart.
They consist of a single-element refracting telescope objective combined with a silver-backed negative lens (similar to a Mangin mirror).
There are several telescope designs that take advantage of placing one or more full-diameter lenses (commonly called a "corrector plate") in front of a spherical primary mirror.
These designs take advantage of all the surfaces being "spherically symmetrical"[5] and were originally invented as modifications of mirror based optical systems (reflecting telescopes) to allow them to have an image plane relatively free of coma or astigmatism so they could be used as astrographic cameras.
The relatively thin and lightweight corrector allows Schmidt cameras to be constructed in diameters up to 1.3 m. The corrector's complex shape takes several processes to make, starting with a flat piece of optical glass, placing a vacuum on one side of it to curve the whole piece, then grinding and polishing the other side flat to achieve the exact shape required to correct the spherical aberration caused by the primary mirror.
The idea of replacing the complicated Schmidt corrector plate with an easy-to-manufacture full-aperture spherical meniscus lens (a meniscus corrector shell) to create a wide-field telescope occurred to at least four optical designers in early 1940s war-torn Europe, including Albert Bouwers (1940), Dmitri Dmitrievich Maksutov (1941), K. Penning, and Dennis Gabor (1941).
[9] His design corrected spherical and chromatic aberrations by placing a weak negative-shaped meniscus corrector closer to the primary mirror.
These elements can be both lenses and mirrors, but since multiple surfaces are involved, achieving good aberration correction in these systems can be very complex.
Smaller companies such as Tamron, Samyang, Vivitar, and Opteka also offered several versions, with the three latter of these brands still actively producing a number of catadioptric lenses for use in modern system cameras.
