[ATM] Dall Kirkham secondary update

["Rod Brackenridge" <rjbr@lycos.com>]

Hi,

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.  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.  

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

Thanks for all the help.

Rod Brackenridge
Mt Martha
AUSTRALIA


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