There are three basic types of telescopes. Refractor, Reflector and Catadioptic (the most common of which is the Schmidt-Cassegrain).

Refractor Telescopes

Refractor type telescope working

Developed in the early 1600s, this is the OTA that was popularized by Galileo Galilei just a few years after the invention of telescope. It has a curved lens in the front that gathers light and bends it to the focal point along the focal length of the optical tube. The light will usually hit a mirror or prism device called the diagonal which directs it to the eyepiece. A focuser moves some part of the optical path in order to bring the light stream to proper focus, creating a sharp image. The eyepiece then magnifies the image and presents it to the eye of the observer or the sensor of a camera.

 

Reflector

Developed by Sir Isaac Newton in the mid-1600s, this uses a mirror rather than a lens to focus the light. A major benefit is that there is no chromatic aberration introduced.

 

 

As we see in the diagram, light enters from the left, hits a mirror in the back which focuses it and sends it to a secondary flat mirror angled at 45 degrees to direct it to the eyepiece. The original design used polished metal but today we use glass as the base that has had an aluminized layer deposited on the glass to create a highly reflective surface,

Schmidt-Cassegrain

SCTs are extremely popular in the hobby market. Sizes commonly run from 4”/102 mm to 16”/400 mm. larger sizes are possible but very expensive.

 

 

The MCT, as shown in the diagram, appears similar to the SCT except that the corrector plate is based on a thicker convex corrector plate design and rather than a spherical mirror as the secondary, a silvered area on the back of the corrector plate handles the reflection back through the hole in the spherical primary mirror.

I chose a Celestron 8SE Schmidt-Cassegrain telescope. It has an eight-inch mirror.  This is how my setup looks