[ATM] Joe Martin's Mirrors

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

I have gotten out of the habit of bragging about the finished mirrors from the NCA mirror- and telescope-making workshop, but Joe Martin (who finished a couple of very nice ones) hinted that he would appreciate having the numbers broadcast to the multitudes on these lists.

His first one was a 6 inch f/8. Here are the averaged numbers from a few readings. My readings have an inherent error of about +/- 0.007 or so.

ROC = 93.5 inches; light source was fixed; the inner zone had an inside radius of 0.3 inches.

zone #     outer radius size      reading
1                 1.5                     0.037
2                 2.12                   0.061
3                 2.6                     0.075
4                 3.0                     0.105

FigureXP says this is about 1/20th wave, with an encircled energy ratio of 0.995, and a strehl of 0.993. Way to go!

The second one took a lot longer. It was a 6 inch f/10 that he inherited from a friend who began the project but didn't finish it - took up another hobby, making beer.
ROC = 118.25, light source also fixed, inner radius of first zone also 0.3 inches.
Zone     outer radius size        reading
1               1.75                      0.017
2               2.48                      0.037
3               3.00                      0.085

Figure XP says this one was about 1/14th wave, encircled energy rtio of 0.992, and a strehl of 0.988.

Very good job on both of these. Now he needs to make the actual telescopes!

BTW, if you make a 6 inch f/8 mirror perfectly spherical, the results, according to FigureXP, are more than acceptable; they are great!

Guy Brandenburg



Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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