Together with colleagues we got this question. Imagine to take small mirrors, the size for example of a dentist mirror, and stick them to a wooden frame with a parabolic shape. Each mirror is flat, and once set of the frame it can be aligned properly with screws so that it redirects its reflection towards the focus of the parabola. All the parabolic surface is covered with these small mirrors.
Now, if you build a Newtonian telescope out of this system, would you get a decent telescope? I expect it to be affected by various aberrations, but would it work ?
Best Answer
The telescope you describe would work in some sense, but it depends strongly on how you define what it means for a telescope to work.
Combining many mirrors to behave as a single large mirror is possible, but those individual mirror segments must still be appropriately curved to achieve good optical performance. When building telescope mirrors for modern astronomy, we are concerned with deviations of the mirror shape from the ideal curve by distances on the order of nanometers. If the whole mirror surface were composed of small flat disks, that would be like using a mirror that deviates from the ideal shape by many millimeters, over it's whole surface!
This sort of thing would be fine for collecting light, and in fact similar systems are used in solar power generation, where one only needs to collect light at some central location, rather than produce an image. In a telescope however, you need very high optical quality to do much of anything.