[winensky]

I use an Astronomik 13nm bandpass Ha and it provides quite natural star diameters, (due to the fact that it picks up a portion of the red end of the spectrum as well), very reasonable exposure times at f/4 and almost complete elimination of light polution/moon light. Also, 13nm filters tend to be less expensive. 4nm will remove more wavelenghts and so further reduce the effects of light pollution and non-systemic noise but at the price of requiring longer exposures. I have included a couple of examples of my Ha stacks I think about 1hr. and 30min.total respectively with my 13nm filter taken with fairly average gear. Hopefully, someone else could post a 4 nm. example.

Cheers.