Re: [ATM] The 16 inch Ultrathin ronchi pics

[Dale Eason <atmpob@yahoo.com>]

We need to know the LPI of the Ronchi grid. 

However I can see that you are getting close to what I
got.  Look at my interferometry report and you will
see the two bumps in the center.   I think you are
also seeing the 1/2 wave surface primary astig as
well.  That is the slight twist  as you go through
ROC.  

I have added ronchi simulation to my analysis
software.  I think it is accurate.  At least it
compares very well with the actuals from this mirror,
Steve Koehler's sim, and Ronchi for Windows sim.

I can turn astig on and off for this mirror while
watching what ronchi looks like.  1/2 surface error is
very subtle.

I will post more in the next few days when the
software is complete.

The worst error I found on that F3.5 mirror was
correction of only 25%.  I think you can also see that
in your ronchi image but that depends on the LPI of
the grid.  If they are 50 to 100 then the lines are
much too flat and too few for an F3.5 I think.

Thanks David.

Dale Eason

--- vorblesnak@peak.org wrote:

> I got the mirror back today and had a half day of
> vacation left so I
> stayed home and twiddled a bit.  I built a video
> ronchi device with a 1/4
> x 20 TPI adjustment.  The final video was about 64
> meg, or 6000+ images in
> AVI, so I pulled some shots for discussion.
> 
> These first one is near the ROC, that was my index
> point.  Then I moved
> one rotation or 1 20th of an inch and paused.
> 
>
http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/Ronchi%20Pictures/ronc001%20ROC2.jpg
> 
> This one seems to show that there is a hump in the
> middle ..
> 
>
http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/Ronchi%20Pictures/ronc007%20Hump.jpg
> 
> This is just inside the ROC one or two 20ths ..
> 
>
http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/Ronchi%20Pictures/ronc008%20one%2020th.jpg
> 
> In you look closly this one seems to show a bit of
> twist in the line ..
> 
>
http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/Ronchi%20Pictures/ronc012%20Astig.jpg
> 
> This is a stacked shot and if you look you can see
> that the center line
> shits a bit between the two images.  Look at where
> it exits the edge of
> the mirror ..
> 
>
http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/Ronchi%20Pictures/ronchi%20compare.jpg
> 
> Finally a line of four posing the question, what is
> in the middle?  I say
> a hump ..
> 
>
http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/Ronchi%20Pictures/What%20is%20in%20the%20middle.jpg
> 
> The mirror did not ship well and the coating has
> gotten somewhat damaged. 
> There are little abrasions here and there all over
> it.  BUT!  There is
> plenty enough left to snag some moon shots when the
> new moon come out.  I
> will also try for a nebula or two.
> 
> Finally, if anyone wants to see the entire ronchi
> movie let me know and i
> will put it on a CD and mail it to you.
> 
> David Davis
> Toledo, OR 97391
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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