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
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