Rob here is an earlier thread on this setup.
http://www.iceinspace.com.au/forum/s...ad.php?t=23971
Below is an image produced by HA and O3 data at an ISO of 1600.
The Borg or Hutech FR/FF flattens the field nicely. Turns the 150mm F5 into an f/4.5. The AP FR/FF should also work quite well and then we will have a 150mm f/3.75!
Bert