When Simon Mitton of Cambridge University Press first suggested this book at the 1991 Riverside Telescope Maker's Conference, I didn't think he was talking to me. For years I'd been primarily concerned with all manner of odd-ball optical devices from satellite tracking systems to airborne telescopes as a professional astronomer. Then it finally sank in that after I'd finished my employer's work I'd go home and drag my trusty little 20-cm Schmidt–Cassegrain (S–C) out in the back yard just to have fun. For a decade and a half it has been part of our family, affording many hours of pleasure and not a little education for my children who have progressed from barely crawling to college entrance exams in the interim.

I believe I saw my first catadioptric telescope during preparations for the International Geophysical Year in the late 1950s. In those days only professionals could own such a glorious and expensive machine. I was disappointed that we students would have to use smaller telescopes to track the yet-to-be-launched first artificial Earth satellite. But I did get to look through the shiny blue and white painted ‘professional’ telescope at times and I vowed that one day I would have one for my very own. Two decades would elapse before I could purchase a used 20-cm S–C.

The aperture of a 20-cm diameter telescope has an area of 314.16 cm.