Re: ATM Figure as a moon crater

["Arjan te Marvelde (ELN)" <Arjan.te.Marvelde@eln.ericsson.se>]

OK, the test was a very quick one, and i haven't even considered the possibility of an edge turned upwards. So I redid it yesterday and the edge in fact IS turned up (with the KE to the right it shows up bright when the center 70% greys out, ronchi inside ROC gives outward hooks). The edge probably has been there all the time as a leftover from fine grinding.
Since the center is still getting more transparent, i guess the edge is not very severe and will polish out in time. A bit more confident now, i'll just follow the simple advice for a while: shut up and polish!

Thanks,
/Arjan



>James Lerch wrote:
>Given your Ronchi results lacked the information of whether you were inside
>or outside of the ROC, its impossible to tell if you have a Turned down edge
>or a turned up edge (it could be either, depending which side of the ROC you
>were on)
>
>I find the Foucault test is the easiest to determine which is which, and the
>Ronchi test the best for seeing how bad (or good) the overall figure of the
>mirror is.

James W. Burrows wrote:
I'll second.  Since Arjan is starting to worry about the figure, it might 
be best to cut out a 4-zone Couder mask (not enough zones for final 
figuring of a 10", but enough for a quick look), and make some measurements 
to see if the surface does warrant worry.  Why not confront the continue 
polish/back to fine grind decision now before too much polish time has been 
expended? - a suggested threshold is 15-20 waves of surface error.  Another 
bugaboo of the thin-mirror set is stress-related astigmatism.