[ATM] Fringe testing Dall Kirkham secondary

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

Hi,

I have just re-joined the list and got back into ATM.  I am working
on a 14inch Dall Kirkham.  I was hoping someone could explain how I
should proceed with testing and polishing the secondary.  The state
of play is:

1)	I have ground and semi-polished the secondary and near fully
polished the reference.  When I place them together, I get about 5
bulls-eye circles covering the disks.

2)	The reference is a good sphere.

3)	Adding tissue paper as wedges, I get arc shaped fringes
across the two disks.  As I press on the edge, I get fewer, more
curved bands and then the bulls-eye pattern appears.

4)	Pressing the centre makes the fringes move towards the edge.

5)	The reference diameter is 104mm and the secondary 100mm.  The
radius of curvature is about 875mm.

Clearly the reference and secondary radii do not match.  What would
be the best way to proceed?

Thanks,

Rod Brackenridge
Mount Martha
AUSTRALIA
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