From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


Tradition is why the large size of the pitch squares.  Porter, et al did it
that way so we should do it that way. I'll note that way back when, the
lens surfaces were polished out with rouge and a burlap sack soaked in
pitch which made for a smaller grain to the pitch bumps (that was about
what they were) than later.  Surface finish was rough because the guys back
then didn't understand too much about the process and generally didn't
worry about getting a good match between the pitch and the glass surface.
Today, we understand a lot more about how the polishing happens and what is
needed for a good optical surface.  We know that it is, to a fair degree,
the edges where the resovoir of compound is that does the planing of the
glass more than the centers.  Thus, the microfaceting is an attempt to
maximize the edges so that the polish happens fast. One of the things to
remember is that it is possible to overload a lap with CeO or rouge and
that can stop almost all of the work on the glass as the glass surface will
just roll over the lap rather than getting planed smooth. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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