[ATM] Ultrathin Project update

[vorblesnak@peak.org]

Dominic-Luc Webb wrote:

> Not sure I totally followed this. I guess you are working an
> optical surface that is 15.5" and:

> 9/64" * 25.4 = 3.57 mm thick

I started this thread last year in February I think.  A search of
Ultrathin will will yield that discussion.  Dale Eason did some excellent
work testing a finished product, and those results are posted.

I wondered how thin I could go.  The 2nd blank is a piece of plate glass,
3/16ths thick that I slumped to a F5.5 curve.  That has since deepened a
bit to 83 inches fl or about an F5.3.  It has also lost some thickness due
to regrinding to correct a nasty distortion brought about by heat and
pressure in the first polishing attempt.

I was interrupted in mid July last year and had to put the project away
till January of this year.

The goal has been to determine how to hand work a thin slumped blank.  How
thin can the blank be.  Techniques must be repeatable.  Simple is better.

> Hmmm. Have you decided how to support this? I would not regard

I have a simple cell I put together out of wood that uses a single ring of
supports at 95% r.  Dale and Mark Holm found errors with this mount but it
is the one I have used all along.  I am using it now to view with the
first mirror. That mirror is good to about 160 power, about 10X per inch
of diameter, then the image begins to go soft.  That could be due to my
poor figuring skills, poor mounting or ???  I intended to use a similar
mount for the 15.5 if I could polish it out and figure it.

> plate glass corrector. Schmidt correctors are not generally
> supported anywhere except the edges.

This fits with what I have discovered in both the 16 inch I use and the
many pie plate mirrors I have ground.  The pie plates perform well if they
are left intact and the plate supported by the edge.  They figure nicely
with a full sized lap mirror on top.  I have though of slumping a pie
plate shape out of a larger piece of glass.

> Here is a variant I am working (two actually):
> http://www.canit.se/~dlwebb/catadioptric/320tdb/320tdb.html

AH! Engineered blanks.  Yours or Richard Schwartz's design?  I have always
wondered how they would work.  I had hoped to have Richard make one for me
but I lost contact with him.

> Just a thought.... if you want a stable support, maybe you could
> rest this optic on broken pieces of glass, similar to my thermal
> diffused optics, but without actually fusing.

I had not though of that!  A pan of fine sand would also work I think. 
Thank you for that suggestion, I will try it before I move on to the full
sized lap.

David Davis
Toledo, OR 97391





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