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Posted by Robert May on August 14, 2003 18:59:23 UTC

The problem with any of the more complex designs is that you have to be able to build an optical surface to a spec. This means that you have to get the ROC of the surface to what the design calls for rather than the typical Newt design where missing the ROC by 5" is just fine.
Test the ROC at the 25 micron stage and all further stages to a very close number is needed.
One way is to make a rod of the length of the ROC and put a dial indicator on the end of it so that it reads at the right ROC (Harbor Freight has their cheap dial indicators on sale for $7 each right now) at some particular length (make a standard which has the exact distance between the two ends) and use it. A medium sized hinge at the other end of the rod will provide a good rotating center for the rod. You will also need to make a mirror cell so that the reading of the indicator stays at the same number if the ROC is correct - having a gradually increasing reading as you cross the optic only makes things worse for reading the ROC.
Good luck and just keep futzing with the optics until you get them right.
You may want to practice on the old glass from the previous attempt in order to get the system down right.

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