What’s a CAT?

Abstract

What allows a Schmidt Cassegrain telescope (SCT) to make distant objects bigger and brighter? Lenses or mirrors or a combination of the two are the heart of any ‘scope. Everything about a telescope, including its capabilities and its price, is determined by its optical design. Before we find out what makes the SCT tick, let’s go back to basics with the simple instruments of Galileo and Newton, the refracting and reflecting telescopes, respectively. The SCT—and the other members of the catadioptric telescope (CAT) tribe—are optical hybrids that combine aspects of these two simple designs, so understanding them is the key to understanding the catadioptric.