I got out to do some Ha imaging today with a camera I just acquired, and I'm getting some pretty prominent Newton Rings. The camera is a Skyris 236M, and it's on a double-stacked SM II 60. I don't see any issues at native focal length, but they are very obvious with a barlow. I've got a couple of those cheap Celestron barlow's that come with the Plossl kits. With one barlow, the rings are bad, and with stacked barlows they are twice as bad. They don't align with each other in the stacked barlow state, so I'm hoping that might indicate it's just the barlows causing the issue? I'm attaching a shot with one barlow below.
I'm wondering if I should try another barlow first, or try to find a way to tilt the camera and see if it resolves the problem. Thoughts?