Isoplanatic focal-length converter for a catadioptric telescope with a meniscus corrector
Sub-aperture lens correctors for single-mirror telescopes
How often do Cassegrain types of telescopes need to be collimated, or under what circumstances (eg. after being carried in the car, shaking, dropping, etc)? - Quora
What is a catadioptric telescope used for? - Quora