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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 pla
by gregfjohnson 10y ago
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!
- wikibob 10y agoThese kind of stories are why I come here. I'm sure we'd all love to hear more interesting history that you'd care to share.
- Stratoscope 10y agoSmall world. I have one of your dad's scopes right here, and I always wondered how they made the optical components. I will think of him the next time I use it.
- ceejayoz 10y agoWe've got one of the NexStar 6SEs here that my kids love to look at Jupiter and Saturn and whatnot with. Thank your dad for us - it's an awesome family activity!
- somebodynew 10y agoDo you know what this process is called? This description makes it sound like the glass has to bend significantly under at most one atmosphere of (negative) pressure, which sounds strange to me. I'd like to read more about it.
- vibrolax 10y agoThe process is called stress polishing. Here's an article about it: http://bobmay.astronomy.net/vacpan/vacpan.htm http://bobmay.astronomy.net/vacpan/vacpan.htm
- nialo 10y agoI think the trick is that the glass actually doesn't need to bend much. Notice that the caption here: https://en.wikipedia.org/wiki/Schmidt_corrector_plate#/media/File:Schema_lame_de_Schmidt.svg https://en.wikipedia.org/wiki/Schmidt_corrector_plate#/media... describes the plate as being hard to tell apart from a flat disk visually.
- xyzzyz 10y agoI had some trouble understanding the exact procedure described above, but then I read the patent[1] for the technique, which was very helpful. [1] - http://www.freepatentsonline.com/3837124.pdf http://www.freepatentsonline.com/3837124.pdf
- X86BSD 10y agoGreg, Thanks for sharing this! As I get older and try to record as much family history I can, I really enjoy you and others sharing what you can about family/company history for the future. Stories like this from first hand accounts are getting harder to find and eventually we may lose these great stories and historical accounts for generations to come. Thanks again!