The Meade ETX 90 is computerized Maksutov-Cassegrain telescopes from Meade Instruments with a 90mm aperture and 1250mm focal length (f/13.9). It’s part of the ETX Observer range that also includes the ETX 80 and ETX 125 models. Compared to the other models in this range the ETX 90 is slightly less powerful than the EXT …
A catadioptric telescopes is one that uses both mirrors and lenses opposed to reflectors that only use mirrors and refractors that only use lenses.
A catadioptric telescope can produce much better images of the night sky than reflectors or refractors but are usually higher priced.