I reckon I need to learn more about astigmatism! Thanks for the initial clarification.
So apart from a 27-point cell and a sling/wire lateral support that we are planning, you'd suggest a manual wavefront jig? How many points and where do you place them? If there's already a thread on CN I'm happy to go thru that.
If your mirror is a very good one, excellent wavefront in a relaxed state... should be no need for introducing tunable forces.
My cheap mirror suffered inherent astigmatism. Many (most?!) mirrors out there do. That's because Zernike Primary Astigmatism is the lowest bending mode of a thin, homogeneous, isotropic solid wafer. (I think I got that terminology correct?!) In layman's terms... just look at a thin mirror cross-eyed and it will manifest astig. Turns out that power and coma don't matter, because they will be focused or aligned out... and the other higher freq and higher order Zernikes take way more force to induce and are (therefore) less likely to be inherent in a mirror.
The choice menu comprises:
>live with it; try to ignore the poor imagery... enjoy observing!
>replace the mirror with a good one
>refigure the mirror at home or have it done
>add an optical (lens) global astig corrector
>stress the astig out of the mirror
Most people opt for #1 = always annoyed, but at least observing
Some people opt for #2 = expensive, should have bought a good mirror to begin with
Some people opt for #3 = redoubtable challenge at home or expensive to have done professionally
Few people do #4, even though it is very easy and works ... probably just never realized that can be done
Few people do #5, even though it is pretty easy and works ... probably just never realized that can be done
When I had the problem... I just thought thru it and came up with options #4 and #5; chose the latter; executed it --- it worked!
At that point I wrote a brief, informal white-paper on the subject and presented it here and there at local astronomy clubs, universities, and aerospace groups.
Some others have since successfully used variations on the themes. Here are a couple of excerpts from that (nearly all the text omitted) >>>
Oooh! Just remembered... I wrote a 4pp article on that, which appears in the Fall 2017 Issue #96 of Amateur Astronomy Magazine.
Highly recommended, complete series available on CD/DVD! Tom
Edited by TOMDEY, 02 September 2019 - 01:34 PM.