From: mjc5{at}psu.edu
To: atm{at}shore.net
Reply-To: mjc5{at}psu.edu


Frank Ward wrote in part:

>Scott, you asked
>>what is the best stroke to use to minimize
>change to the figure?<
>
>If I did not want to change the figure by polishing
>the existing surface with black rouge I would wave my
>hands over the mirror and tool as they sat on the disk,
>other than that you are going to have to obey the laws
>of physics. Polishing is the "result" of changing the
>surface. I don't know the diameter of your project and
>how hard it was for you to get to where you are....but
>I often go hyperbolic or ellipsoidal on purpose and
>from there to parabolic. You can too, and end up with a
>fine polish, fine edge, and good figures in the teens. The
>best way to start is to go in one direction with the mirror
>on top and then repeat with the mirror on the bottom. Don't
>go too far in either direction and you will come close to
>where you are.

        Correct, that surface we are making is so precise, and the
difference between sphere and parabola so small, that pretty much any
polishing action is going to affect the figure. If I wanted to finish up
with rouge, I would take the mirror back to spherical, perhaps with rouge,
then work it again to the parabola.

        Which brings me to ask, Frank - is there any value to
attaining the sphere with CEO, then parabolizing with rouge? I didn't know
if there would be enough time in that step to get the surface that you can
get with rouge. It would certainly be a benefit to have the parbolizing go
slower.

        - Mike -
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