Re: [ATM] Dall Kirkham secondary update

[Mike Lockwood <melockwo@uiuc.edu>]

Rod,

Rod Brackenridge wrote:
> Last week several people assisted me with my confusion over testing and
 > working a convex secondary.  As Bob May advised, I used longer strokes
 > in order to reduce the convex secondary's edge.  With my original hard
 > lap there was no change in the surface.  I then made a softer lap and
 > work is progressing nicely.  The number of bulls eye fringes gradually
 > reduced and now I have 8 fringes over the secondary.

That's good progress.  Nice work.

> They are not
 > straight.  There is a hump in the centre and a slight trough further
 > out, both a little under a half a fringe in size.  I think this is
 > caused by zones on the reference. Someone else tested my reference
 > sphere and noted a slight hill and ring I had not seen when using
 > a ronchi grating.  They were just visible with a foucault test.  I
 > think these zones are caused by my polishing machine.

Probably the easiest thing to do is just test the reference "sphere" 
with a knife-edge tester.  Any zones should be obvious.  Work by hand 
until you have a good sphere, then test again.  If you get a nice even 
null, you can be certain you have a good reference.

> I intend to work the reference by hand and remove the zones.
 > Hopefully I will then have nearly straight lines.

Ronchi works too.  Focault may be a little more sensitive for this 
application.

	Mike Lockwood

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