Pasting this from a recent post of mine...
Ha isn't the easiest on a DSLR that's for sure - checking focus between each shot in the absence of a bright star in the FOV is going to be a nachtmare!!!!
http://www.iceinspace.com.au/forum/....milies/lol.gif
I developed a little routine to help with the "user" program of Synscan which makes life a tad easier (just a tad mind!!) Find a bright star without Ha filter - set it as user object 1. GoTo and Frame the object you want to image - set it as user object 2. Go back to obj 1 (bright star), insert Ha filter into imaging train, focus, slew back to obj 2 - start imaging!!!! Simple Eh!?
http://www.iceinspace.com.au/forum/..../rolleye09.gif
(I'm using EOS clip in filters on my 40D Trevor)
The bugger is that if you use this to method to focus in-between shots, you stuff around with the guiding a bit too much.
Doug