Quote:Surprisingly, I think I have the problem licked! the only things I've done are
- re-did the collimation, still by eyeball using a Kodak film canister, since my laser is still a week or two out;
- I reinforced the focuser with an aluminum plate underneath
- I relocated the locking knobs for the main mirror (drilled and tapped new holes right next to the collimation knobs) so that tightening the locking knobs doesn't throw the collimation off as much as it used to
Here's a single 5-minute unguided sub of M27:
Stars are "round enough" over most of the field. What this tells me is, the 2" Keller reducer's performance drops off fairly rapidly once you get beyond the 22mm image circle.
ASA has always said the imaging circle is 22mm, but my sensor is APS-C (24x16mm, QHY8) and it's obvious that the stars streak out in the extreme corners.
but Powernewts (which use the same corrector) claim to cover APS-C. It's obvious to me that they don't, at least not to the very corners.