Here is a thread with narrow band image taken with the Skywatcher 150mm F5. Below is a small image taken with HA and O3 narrowband filters.
http://www.iceinspace.com.au/forum/s...ad.php?t=23971
Also a star test
http://aberrator.astronomy.net/scope...tor_150_3.html
I don't know how good these are but they sound interesting.
http://www.scopestuff.com/ss_trzw.htm
The four inch focuser would be great as there is no vignetting.
bert