The Large Binocular Telescope uses two curved mirrors to gather light
Light path in a Schmidt–Cassegrain
Schematic of a Keplerian refracting telescope. The arrow at (4) is a (notional) representation of the original image; the arrow at (5) is the inverted image at the focal plane; the arrow at (6) is the virtual image that forms in the viewer's visual sphere. The red rays produce the midpoint of the arrow; two other sets of rays (each black) produce its head and tail.
View of the corrector and primary mirror of a Schmidt–Cassegrain.
Eight-inch refracting telescope at Chabot Space and Science Center
People demonstrating a Schmidt–Cassegrain telescope at a sidewalk gathering
The Keck II telescope gathers light by using 36 segmented hexagonal mirrors to create a 10 m (33 ft) aperture primary mirror
These eyes represent a scaled figure of the human eye where 15 px = 1 mm, they have a pupil diameter of 7 mm. Figure A has an exit pupil diameter of 14 mm, which for astronomy purposes results in a 75% loss of light. Figure B has an exit pupil of 6.4 mm, which allows the full 100% of observable light to be perceived by the observer.
Two of the four Unit Telescopes that make up the ESO's VLT, on a remote mountaintop, 2600 metres above sea level in the Chilean Atacama Desert.
Comparison of nominal sizes of primary mirrors of some notable optical telescopes
Harlan J. Smith Telescope reflecting telescope at McDonald Observatory, Texas

Telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electronic image sensors.

- Optical telescope

Their high f-ratio means they are not a wide-field telescope like their Schmidt camera predecessor, but they are good for more narrow-field deep sky and planetary viewing.

- Schmidt–Cassegrain telescope
The Large Binocular Telescope uses two curved mirrors to gather light

2 related topics

Alpha

A 150 mm aperture catadioptric Maksutov telescope

Catadioptric system

One where refraction and reflection are combined in an optical system, usually via lenses and curved mirrors (catoptrics).

One where refraction and reflection are combined in an optical system, usually via lenses and curved mirrors (catoptrics).

A 150 mm aperture catadioptric Maksutov telescope
Light path in a Schmidt–Cassegrain
Light path in a meniscus telescope (Maksutov–Cassegrain)
Houghton doublet corrector design equations – special case symmetric design.
Light path in an Argunov Cassegrain telescope
Example of a catadioptric lens using rear surfaced "mangin mirrors" (Minolta RF Rokkor-X 250mm f/5.6)
An example of 'iris blur' or bokeh produced by a catadioptric lens, behind an in-focus light.
500 mm catadioptric lens mounted on a Yashica FX-3
Minolta AF 500 mm F/8 catadioptric lens mounted on a Sony Alpha 55 camera
Samyang 500mm f/8

Catadioptric combinations are used in focusing systems such as searchlights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes, and telephoto lenses.

Schmidt–Cassegrain telescopes are one of the most popular commercial designs on the amateur astronomical market, having been mass-produced since the 1960s. The design replaces the Schmidt Camera film holder with a Cassegrain secondary mirror, making a folded optical path with a long focal length and a narrow field of view.

Diagram of Schmidt camera

Schmidt camera

Diagram of Schmidt camera
The 77 cm Schmidt-telescope from 1966 at Brorfelde Observatory was originally equipped with photographic film, and an engineer is here showing the film-box, which was then placed behind the locker at the center of the telescope (at the telescope's prime focus)
The 2 meter diameter Alfred Jensch Telescope at the Karl Schwarzschild Observatory in Tautenburg, Thuringia, Germany is the largest Schmidt camera in the world.
One of the Baker–Nunn cameras used by the Smithsonian satellite-tracking program
A Baker-Nunn satellite tracking camera in use.

A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations.

The addition of a convex secondary mirror to the Schmidt design directing light through a hole in the primary mirror creates a Schmidt–Cassegrain telescope.