My dad (Tom Johnson) founded Celestron. His key idea was a way to create the corrector plate at the front of a Schmidt-Cassegrain telescope. The corrector plate compensates for spherical aberration (the difference between a parabolic main mirror and a spherical main mirror). This is a very complicated curve, and the traditional way to make it was to have an optician make it by hand. This was an arduous and time-consuming process. Tom's idea was to spend that time manually creating a block that has the OPPOSITE shape from the one desired, and carve narrow grooves in it. Then, take a normal optical-quality sheet of glass, and use a vacuum to deflect that glass down onto the block. Grind the exposed surface flat, which is a quick and easy thing to do accurately. Release the vacuum, and out pops a piece of glass that is a high-quality corrector lens. As a kid, I can remember many weekends when my dad was out in the garage grinding lenses and refining the idea. Eventually Celestron became successful enough to allow him to quit his day job!