Saturday's ATM session was quite busy. Charlie and Josh were there and my photographer neighbor also came at the end. Charlie brought his 13" mirror to look at with the knife edge and ronchi screen. This is an f9 mirror, so the ROC was nearly 20 feet! By angling diagonally across my garage, we were able to get it set up for testing. It showed a pretty healthy turned down edge, but that is a workable problem. Charlie is concerned that the mirror is astigmatic; neither the knife edge nor the ronchi tests are really critical tests for astigmatism, and unfortunately I do not have a 'stig tester (got to make one someday...) I did see some evidence of astigmatism in the ronchi test, so Charlie's concern's may be justified. The best test for astigmatism is to do a star test with the mirror in a working telescope, and so Charlie is motivated to build the 'scope now and test the mirror. As some of you may know, the only cure for astigmatism is to go back to at least 320 grit and fine grind again. When this telescope is finished it is going to be incredible. An f9 13" Newtonian - wow! I will definitely be in line to be one of the first to look through it. Josh brought his 8" f8 (measured by us to be within 1/8 of inch of f8) mirror he picked up for a song on KSL.com. The coatings are in rough shape and do need to be redone. The figure looked quite good, but we did not do a Foucault test, just viewed it with a knife edge tester and ronchi screen. Josh really picked up the concept of the knife edge quickly and he is very motivated to grind, polish and figure a big mirror (18" is his plan). At the moment, his plans are to refigure the 8" he has so that he can get experience doing it then move up to a big mirror. Work was also done by Josh and me on my 4" f4 finder project. It is in the final figuring stages and the center was a bit high. Josh and I walked the barrel working the center with C.O.C strokes with a tool sized at ~ 50% of the mirror for about 15 minutes. This pushed the center down well, but left it a little rough. Later that day, I smoothed it out and tested it to be around 1/8th of a wave (P-V wavefront). It is still a little rougher than I like, so will continue with very light strokes and very fine CeOx. My neighbor, a photographer, came by to look at a barn-door mount. This might get him started in astrophotography, then he can spend big bucks later... At that point, it was time to close up the shop after a very good ATM session. The next session is on Oct. 15th from 9:00 AM to noonish. As usual, email me off list at mat.hutchings@siemens.com and I will give you directions to my house. Mat ---------------------------------------------------------------------------- This message and any included attachments are from Siemens Medical Solutions and are intended only for the addressee(s). The information contained herein may include trade secrets or privileged or otherwise confidential information. Unauthorized review, forwarding, printing, copying, distributing, or using such information is strictly prohibited and may be unlawful. If you received this message in error, or have reason to believe you are not authorized to receive it, please promptly delete this message and notify the sender by e-mail with a copy to Central.SecurityOffice@siemens.com Thank you