Re: [ATM] [atm_free] Detecting Astig in Ronchi images

[Mike Lockwood <melockwo@uiuc.edu>]

Mel,

Mel Bartels wrote:
> To say what I key off of is difficult because it is not a conscious process.
> I could point you to the bend in the Ronchi bands that smell like 1/2 wave
> on the surface error (in this case, not zonal therefore must be higher order
> 'stig; furthermore, play with a Ronchi plotting program and see what a 1/2
> wave surface error looks like, then project that error into a single banding
> wave), and I could point you to several spots in the image that indicate 45
> deg angled axes.  But I don't know how useful because it's a post-hoc
> explanation of what I 'see' in the back of my mind.  I'm happy to continue
> this dialogue if you want to zero in on specifics.

Actually, I think that if you could comment briefly on specific 
features in each photo, those comments, if added to Dale's web page, 
would make an excellent reference document that many would appreciate 
and could learn from.

To me, the only real dead giveaway for something bad going on (other 
than a generally uneven, rough surface) is in the fourth photo, where 
the slightly off-center line has markedly different behavior on either 
side of line near the top of the mirror.
   http://home.comcast.net/~doeason/DDavis/ronchi_scan.htm

To me that indicates some more "organized" badness.

Dale, by the way, the sixth and eighth photos are still broken in my 
browser (bottom two photos in right column).  ;(

If the important features were shown there, then I couldn't see them.

	Thanks,

	Mike Lockwood

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