New Main: Cassegrain

Cassegrain telescopes are a type of reflecting telescope that use a combination of mirrors to form an image. 

The design of a Cassegrain telescope typically involves a concave primary mirror at the bottom of the telescope, which gathers and reflects light. A secondary mirror, which is smaller and convex, reflects the light from the primary mirror and directs it through a hole in the center of the primary mirror. The eyepiece is located at the back of the telescope, where the light is focused and magnified.

Cassegrain telescopes are popular among amateur astronomers because they offer a relatively compact design with a long focal length, which allows for high magnification and sharp, clear images. They are also commonly used in professional astronomy because of their large aperture and high resolution, which make them ideal for observing distant objects and studying the details of celestial bodies.

Cassegrain telescopes and Schmidt-Cassegrain telescopes (often abbreviated as SCTs) are both types of reflecting telescopes that use a combination of mirrors to form an image. The main difference between them is in the design of the secondary mirror.

In a Cassegrain telescope, the secondary mirror is convex and located in front of the focal point of the primary mirror. This design allows for a wider field of view and is more suitable for observing extended objects such as galaxies or star clusters.

In a Schmidt-Cassegrain telescope, the secondary mirror is located at the center of the primary mirror and is a special aspherical shape called a Schmidt corrector plate. This design corrects for spherical aberration, which can cause blurring and distortion in the image, and produces a wider, flatter field of view that is more suitable for astrophotography.