What’s a CAT?
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What allows a Schmidt Cassegrain telescope (SCT) to make distant objects bigger and brighter? Optics: 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 SCTs tick, let us 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.
The Refracting Telescope
In the beginning, there was the simple refractor, the lens-type scope that was probably first turned on the heavens by Galileo Galilei on a mythic Italian evening in 1609. Galileo did not invent the telescope and may not even have been the first person to use it for viewing the night sky. He wasthe first...