Re: [ATM] The 16 inch Ultrathin ronchi pics

["Jerry" <wa4guu@verizon.net>]

Have you tried sticking a knob to the back of the mirror, to use as a handle
for stroking. Maybe about 2 or 2 1/2 inch in diameter, cut cylindrical on
the side in contact with the glass, stuck with pitch to the back of the
mirror.  Seems to me this might keep your hand from warming the glass and
deformations in the middle caused by the handle would likely be in the
secondary shadow. It would give you more control of the glass when far
offset on the lap, like when you would be when you are correcting the
center. If you corrected the center you would then be somewhere around 60%
corrected. The curve might smooth a bit when you get the center correction
closer to the correction in the outer zones. 

Jerry. 



-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
vorblesnak
Sent: Saturday, February 25, 2006 11:51 PM
To: atm@atmlist.net
Subject: [ATM] The 16 inch Ultrathin ronchi pics

Steve Koehler wrote ..

> David,

> These are nice Ronchi images, and show a lot.  I agree that the line 
> leaning is clear in your comparison image.

> I'm still curious what you intend to do about getting the correction 
> closer.  Do you see the evidence in the Ronchi images of 
> undercorrection?  If you figure from Ronchi, how do you intend to

In image one and two I see a central hump that extends out the 50% / 60%
zone.  This seems to be supported by the lines shown in the line of four on
the last set of images.  That kink is an obvious zonal error.  The 
lines are about the same width though so the ROC between the zones is very
close.

> measure the correction to address that problem?  From Dale's analysis, 
> the correction error is several times more objectionable than the 
> astigmatism.  I wouldn't worry about the astigmatism too much until 
> that  is brought under control.

The problem is two fold.  What is causing the astigmatism and what is 
causing the false positive.  Heat could be at the root of both.  I am 
working on two pie plates right now attempting to replicate the error that
is in the 16.  I have caused astigmatism in the one.  It increased as I
moved closer to correction, decreased as I polished back towards a sphere.
At this point I cannot discount anything.  I am considering working in water
to add mass to pull off the heat.  I will take what I learn from the pie
plates and use it on the 15.5.  I probably won't 
touch the 16 for a month or better so no need for a comparative ronchi just
yet. 

> If it seems useful, I will run 50 lpi Ronchi simulations with your 
> mirror and with a perfect f/3.5 for comparison.  I won't be able to 
> get to this until Monday, however.
> --
> Steve Koehler

David Davis
Toledo, OR 97391

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