[nebulosity. (Jo)]

G'day

I've got a nice Nikkor 85mm 1.8 lens that I use for wide field imaging and as Im about to make a mono DSLR I was wanting to do a bit of NB with it as well. I thought I would start looking around for a Ha filter but am not sure how narrow to go, I have seen ones from 40nm to 3nm and am wondering what would be best.

Also, I generally use the lens at f4 because of CA but with the filter CA wouldn't be a problem? So I could use it at f1.8? (its still tack sharp right to the edges)

Now, I was thinking about a clip in filter (camera's a 350d) but wondering if it would work OK at f1.8? The other option would be to get a 2" filter and attach it to the front of the lens, what do you think would be best?

Thanks
Jo