What is a folding reflecting telescope?

Reflecting telescope is an astronomical telescope composed of refraction and reflection elements. In which a single refractive or reflective element cannot image well.

In 18 14, Hamilton proposed adding a reflecting surface in the middle of the lens group to increase the power. In this way, ordinary glass can be used to obtain a telescope with better chromatic aberration correction than the achromatic objective. This is the earliest folding reflecting telescope. Because other aberrations can't be improved, there is no further development. At present, reflective telescopes mainly refer to the most widely used Schmidt telescope, Maksutov telescope and telescopes derived from them, such as super Schmidt telescope and Baker-Nohn camera. This telescope has the advantages of strong optical power (the relative aperture can reach 1, or even larger), large field of view (up to 30 ~ 50), and small aberration. , usually used for sky survey photography and observation of diffuse nebulae, meteors and satellites. Seglin catadioptric system is often used in compact small visible astronomical telescope.

Schmidt telescope was invented by Schmidt in 1930 for astrophotography. A spherical concave mirror is mainly used as the main mirror to eliminate coma, and an aspheric lens placed in a proper position in front of the main mirror is used as a corrector to correct the spherical aberration of the main mirror. In this way, a wide-angle field of view (up to 40-50 degrees) can be obtained, without spherical aberration and coma, which are common in general mirrors, only slight chromatic aberration produced by the correction mirror.