On a similar note, a very experienced atm friend uses a trick which may be old hat but I have not seen reference to before...he "tunes" out a bit of spherical abberation in his primary by heating the back side at a certain radius with a ring of resistors with a series reostat to control the power. I witnessed a before/after star test at various power levels and walked away impressed if not totally convinced. I am guessing (if this really works) that he achieves some sort of differential heating across the mirror. Anyone have any experience with this sort of thing?
Steve