grimble_cornet

These are the results I used to get with the ASI120MM in Ha - I even got them in CaK if I used the dreaded x2.5 Powermate which is famous for exacerbating the problem! The tilt adapter image came from an article I read at the time - sorry I can't remember who I 'borrowed' it from - but it reflects my own experiences. I bought an early, commercial tilt adapter but had to fit longer bolts to get enough tilt. Without a Barlow or Powermate I could just about get rid of the Newton's rings by tilting and using flats but it was hard to maintain focus across the fov. Incidently, just reinforce Merlin's comment - my very early ASI120MM did not have a 'window' and produced the most extreme Newton's rings of any camera I have tried. Mike

I gave up trying to solve the Newton's rings problem with the ASI120MM years ago having tried tilting (needed almost 5 degrees and even that didn't work with Barlows or Powermates), flats and even Fourier transforms. Eventually bought a Point Grey Grasshopper CCD camera which has given me great results for over 5 years. I bought an ASI290MM a couple of weeks ago for EAA use but decided to try it out with my Lunt 100Ha on the large prom. Yep.......... the Newton's rings are there but not as bad as with the 120MM. I managed some prom images without any correction and the much faster frame rate (compared to the Grasshopper) could be a real advantage.