A Schmidt-Cassegrain telescope has multiple optical elements: a spherical primary mirror, a hyperbolic secondary mirror, a Schmidt corrector plate (aspheric lens), and sometimes a field flattener lens to create a planar image. Could you make all of these out of one solid piece of glass?
Amazing! Especially so considering how little use my 8 inch Meade Schmidt-Cassegrain amateur telescope got over the years because of its weight and awkward handling characteristics. One person couldn’t set it up and take it down very easily. It was an early model with an equatorial wedge and tripod, made before the now universal “go-to” function. Compared to these tiny unitary units, it definitely suffered from the fact that the various parts cooled (and deformed) at different rates. Of course, the best nights for astronomy are those clear nights when radiational cooling tends to be intense - often right after passage of a cold front.