Subject: [interferometry] Digest Number 1053
Date: 3/13/2008, 8:49 AM


Messages In This Digest (3 Messages)

View All Topics | Create New Topic



New file uploaded to interferometry

Posted by: ""

Thu Mar 13, 2008 12:26 am (PDT)


This email message is a notification to let you know that
a file has been uploaded to the Files area of the interferometry

File : /John Abrahamian/Comparison of 6th session to 7th session Astigmatism Work.doc
Uploaded by : owl1820002000 <>
Description : Removing astigmatism thru surface mapping and machine polishing.

You can access this file at the URL:

To learn more about file sharing for your group, please visit:


owl1820002000 <>


Removing astigmatism thru surface mapping and polishing by machine

Posted by: "John Abrahamian"   owl1820002000

Thu Mar 13, 2008 12:46 am (PDT)

I've uploaded my results from my attempts at removing astigmatism from
the 25" BVC glass. The procedure entailed getting Zernike terms from
OpenFringe using my Bath interferometer, then inputing the data into
James' astigmatism removal spreadsheet. Some of the terms signs were
changed in the spreadsheet to represent the mirror orientation on the
test stand and OpenFringe models (thanks to Steve Koehler). I then
translated the spreadsheet work to my polishing machine, using a 6"
and 8" lap with soft pitch on them. I made them from aluminum and cast
iron. The 6" cast iron lap works really smoothly with no chatter. I
made it from a 5lb flat barbel weight. I used the 6" lap for work at
the very edge then switched over to the 8" lap when I could safely
without turning the edge. I locked the overarm over the various radial
positions and worked thru the stroke chart, rotating the freewheeling
turntable back and forth over the required zones marked in the degrees
which match the spreadsheet.

I believe I've gotten some nice results as the
surface map is getting more symmetrical. I have a description of how I
achieved my results in the Word document. It would be nice to leave
the astigmatism frustration behind me and actually get back to putting
a decent figure onto the glass but the work performed actually went
fairly quickly after I correctly labeled the polar coordinates onto
the mirror edge. The spreadsheet and OpenFringe are now in agreement
and I think good things can come from this combination as I really
hate to have to go back to regrinding again. The document is rather
large and I can remove it soon if the group moderators wish it.

It is here:

And is named: "Comparison of 6th session to 7th session Astigmatism
Work.doc "

The results were derived from 5 igrams imaged with many fringes
present. The wavefront files were averaged to achieve the results.
They are all from one orientation on the test stand.

All comments welcome, John Abrahamian


Re: Removing astigmatism thru surface mapping and polishing by machi

Posted by: "Stephen Koehler"   steve_koehler

Thu Mar 13, 2008 8:20 am (PDT)


> I've uploaded my results from my attempts at removing astigmatism from
> the 25" BVC glass.

Fantastic! The astigmatism has gotten so low that I thought, at
first, that you might have turned off the astig terms again. I
analyzed the sample interferogram and convinced myself that you have
done it right. I think you're very fortunate that most of the astig
came out in one session. Congratulations.

The astig is now much less than the remaining correction. I used
OpenFringe to estimate it as 1/9 wave RMS. It's oriented mostly
vertically, so it may very well be test stand astigmatism. Once you
get the correction closer, you need to start analyzing multiple
orientations to get the test stand astig out of the picture.
Steve Koehler

Recent Activity
Visit Your Group
Yahoo! News

Fashion News

What's the word on

fashion and style?

Yahoo! Finance

It's Now Personal

Guides, news,

advice & more.

Dog Fanatics

on Yahoo! Groups

Find people who are

crazy about dogs.

Need to Reply?

Click one of the "Reply" links to respond to a specific message in the Daily Digest.

Create New Topic | Visit Your Group on the Web
Messages | Files | Photos | Links | Database | Polls | Members | Calendar
Yahoo! Groups
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Individual | Switch format to Traditional
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe