Hmmm. I'm glad to say, Bill, that I don't suffer from that problem. The SM40, ED80, B1200 combo is exceptionally flat wrt gradients. The PST has a bit of a sweet/hot spot, so I'm really enjoying using the SM40 on the ED80
.
I guess I can't assume that a larger Ha filter will still be flat when I go to upgrade...
Have you tried to devise a way to take a flat frame with a Ha scope?
Al.