[ATM] Ronchi images and figuring help

[TONY BLAKESLEY]

Thanks for the input.

I am 100% certain it is not astigmatism. I have had a mirror with astigmatism in the past and I learned a great deal from fixing it. This mirror is constantly rotate and is spun on a turntable on the grinding machine. It is also a full thickness pyrex mirror so the test stand isnt introducing any astigmatism into the ronchi image.

Again im sorry for the poor quality image. It is way out of focus and I had to rotate/stretch/skew the image to format it onto the web to a decent size. 

I will continue to deal with the edge problems as you and Mel Bartels mentions. 

Thanks,

Tony

--- On Sat, 6/6/09, Jerry <wa4guu at verizon.net> wrote:

From: Jerry <wa4guu at verizon.net>
Subject: RE: [ATM] Ronchi images and figuring help
To: "'TONY BLAKESLEY'" <blaktony86 at yahoo.com>, atm at atmlist.net
Date: Saturday, June 6, 2009, 12:30 PM

There is some astigmatism showing and some roughness remains.

A picture of the pitch lap can help sometimes for me and others to see if it
may be trimmed in a manner that will improve results.

The astigmatism is seen by the S shaped nature of the bands, particularly
the central band.

The roughness is seen in the alternating change of the width of the bands.
With Ronchi testing alone it is difficult to see if it caused by zones or
ripple.

If the astigmatism is not induced by stress on the test stand, you will
probably work to get the astigmatism out and change the entire mirror from
this present condition. Test the mirror on several diameters and see if the
astigmatism rotates with the mirror and shows the same when the mirror is
positioned the same.

If you decide the astigmatism is from flexure on the test stand:
The outer 25% or so is overcorrected compared to the simulation. If this is
the 9" f:6 mirror you had mentioned in the past it might not be
overcorrected so much that it would make the mirror un-acceptable. But it
probably is a bit too much. You can view the defect as being a high
intermediate zone. If you can push that down you will have a better fit with
the simulated Ronchi. There are others here who know more about machine
figuring than me.

Not having seen what you had before this, I would not want to say how you
might fix it. You say it has gotten better so I would say continue with what
you have done and see if it gets even better.


Jerry



-----Original Message-----
From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of
TONY BLAKESLEY
Sent: Saturday, June 06, 2009 10:35 AM
To: atm at atmlist.net
Subject: [ATM] Ronchi images and figuring help

Hello,

I am deciding whether to parabolize my mirror now or try and make a perfect
sphere with a perfect edge first. I have been combating TDE for a few weeks
now. The ronchi image of the TDE before was pretty bad, the edges hooked
severly. I also had a bad central hole. After completing my modified
Mirror-o-Matic grinding and polishing machine, I polished for a few hours
trying various methods to knock down the TDE. I know have a very smooth even
figure with which appears to be a rolled edge. It matches closely to the
computer generated ronchi images. I would like to call upon the ATM gurus
knowledge and expertise to lead me to whether I should continue spherizing
and try to get that perfect edge, or to go ahead and continue on to
parabolization. View my ronchi images here:

http://blaktony86.fortunecity.com/ronchitesting.html

Thanks for the help guys,

-Tony
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