Very popular Schmidt-Cassegrain telescopes are reflecting telescopes with a unique Schmidt corrector lens which eliminates aberrations. Schmidt corrector is a thin, aspheric lens used to correct the light paths – all light is brought to the same focus.
The tube of this type of telescope isn't very long, but because of the unique folding of the light, the focal length can be pretty long.
Design of Schmidt-Cassegrain telescope. (Available from:http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/phy217_tel_catadioptric.html. [accessed 29 Oct, 2019] )
Schmidt-Cassegrain telescopes are great for lunar and planetary viewing. They can also be used for “deep-sky” observing and astrophotography.
Compare to refractors, they feature large apertures at reasonable prices. They are easy to use, very compact, and portable.