From: Dominic-Luc Webb 
To: Thomas Janstrom 
cc: atm 
Reply-To: Dominic-Luc Webb 


On Wed, 2 Apr 2003, Thomas Janstrom wrote:

>
> Ok I now have my DK secondary ready to test, at a first glance (no wedges
> used) I get about 26 fringes neatly centered. With wedges I get arcs, and I
> mean lots of them, far too many to count. I have tried several wedging
> options, some with as small a difference as 2.5microns, the largest was
> 0.1mm, in both cases there were more fringes than you would want to have to
> count.
>
> What should I do to bring the fringe numbers down (this question is only RE:
> using an air wedge) Tex suggests a shallow wedge, but I tried that....
>
> Secondly what is the recommended polishing technique to steepen a convex
> curve?
> Clear skies, Thomas
> http://www.tjanstrom.com
> "Don't make me set the laser printer to stun"


I am working some F/1.0 to F/1.5 glass (Schmidt primaries) in 310 mm range.
My polishing tool is a disk with triangles cut on the edges, so it looks
kind of like a gear. This pretty much completely eliminated my TDE problem,
which was a lot of waves of error from beginning. I went back to grinding
to get the glass round again, and did fine grinding and polishing on this
polishing tool. I have an optimistic opinion of cutting into tools. Aside
from the general routine of 1/3 diametral strokes, I could suggest
considering holes at strategic positions, perhaps in the middle in your
case. I even use multiple tools to optimize contact at the surfaces I am
most interested in with decent success. The final stages requires good
pressing to make sure tool and mirror have good contact. Some people might
dismiss my method, but I would urge people to experiment with cutting into
their polishing tools (not plural, tools).

Dominic

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