Re: [ATM] subdiameter lap controversies?

["Bob May" <rmay@nethere.com>]

The fun you are running into is that parabolizing is more of an
art and different people have figured out different ways to get a
good figure.
I myself use a full sized lap and just increase the stroke length
a bit to get  the parabolizing stroke, checking along the way to
insure that there is no sudden hole in the center without the
edges of it being "sharp" to the rest of the surface.  Typically
a 1'3d stroke will produce a sphere and going longer will start
making an ellipsoidal surface.  When you hit the right stroke
length, the parabola becomes the surface for a while which then
can turn into all kinds of other things.
The thing with subdiameter laps is that they can work on one area
and leae other areas alone for the most part.  The pros use
subdiameter laps exclusively as they are doing huge surfaces
relative to what we are doing and they use a computer control
with that lap to erode the high spots that they see with
interfrometry of the surface.  All highly commplex but it works
and works well if you can put up with the little disconuitys that
can happen if you don't analyze the mirror enough.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net


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