Re: [ATM] help with DK secondary

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

The bullseye should always come towards the edge when pressing
down on it.  The quistion is what happens when the pressure is
put on the center of the bullseye.  If the rings come towards the
bullseye, then the surfacee isn't convex enough and you are
decreasing the distance between the two surfaces.  If the rings
wasl away grom the bullseye then the center is the most close to
the tesst plate and the decreasing distance just is that and the
rings walk away as they are saying how far the two plates are
from teach other and pressure is getting all of the surface
closer to each other.
To get the convex surface to a shorter ROC, hang the polishing
tool way off to the side and just do a chordal stroke.  Almost
half on is about right to get things started in the right
direction, worry about gettin g a good sphere later after the
number of rings goes down.  You will pribably go through a phase
where the edge is rolled down and thus the direction of the rings
changes and this is the point where you really need to get back
to a spherical surface with moree COC strokes to find out where
you are.
Good luck here as I'm working  with a cuy to get a pair of 13"
lenses to a particular ROC and match curvature within a few
fringes.  We're down to about 6 fringes now and a little bit of
astigmatism.
Bob May

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


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