Optics- Mirror Making
At the heart of every great reflecting telescope lies the primary mirror. You can buy a commercial mirror that will give 'OK' images or 'pretty good' views at a very reasonable cost. But the stars will not be tack-sharp. The craters on the moon will be a little blurry, leaving you to want more. To really see planetary details and to really get the best resolution possible, you need to spend thousands of dollars for a great commercial mirror. Its the same as hi-fidelity stereo equipment or autos, or any other human endevor. To make the best requires thought and time. And the best made things are often still hand-made. Nowhere is this truer than in optics.
You can make a mirror that exceeds the specs of most commercial mirrors for a mere fraction of the price by investing some of your time. Here's a journal and some instructions on how...
Grinding A Mirror