Quote:
Originally Posted by Orion
Mark when using a machine would you still need to do the figuring by hand or are there some mirror manufacturers that don't bother?
I have never used a machine so I wouldn't know, but I can't see it doing the figuring.
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A great deal of figuring can be done by machine. On smaller mirrors 10" to 12 " of modest asphericity it can actually be done with one polisher and a skilled operator all by machine .
In my experience a smoother zone free finish can be had with hand work and I'd guess I do 50% by machine and 50% by hand on my mirrors, as I like to take the figuring process from engineering science into art and a handcraft.
Large fast pro mirrors ( like the 8meter varieties ) are polished by computer controlled laps which actually warp to fit the shape of the mirror. They are not touched by the human hand.
As a contrast in technologies , the final corrective polishing runs on the 200 inch ( 5 metre ) Mt Palomar were done in 1947 by the late Don Hendrix by hand using 6" polishers. As the rib thickness had come out uneven in the casting, the mirror performed worse in its cell on the sky than it did hanging vertical on the test stand.
The final touches were made by taking `foucault-grams' on a star, where a knife edge null test was made on a real star and captured on a photograghic plate. The final rubbing down of the 1 wave high edge evident from the mirror `in-situ' in the Palomar observatory by Don Hendrix. Thats what I call `flying by the seat of your pants '
