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Hi Doug,
Nice effort.
You can also use the transform function in Photoshop. Not that easy to use but with patience it will do it. Get the RGB as base image. Now make a new layer and paste the Ha into it. Now hit control T to turn on the transform mode. Now you will see little arrows that show the directions you can manipulate the image. I think if you right click you get a menu and you want all directions enabled. I zoom in and then you can see what you are moving. Change the blend mode to something like lighten so you can see the 2 images. Photoshop I think seems to "click in" when you are close but I could be imagining that! It can be difficult to get it right but with patience you can. Perhaps alignment in CCDstack or Images Plus first would be far easier. I sometimes use it if I forgot to align an layer like Ha and it is close to being aligned.
Send me a PM and I'll let you in on a Ha blending approach I developed.
Otherwise blending Ha can be a pain and not well written up and you'll get odd colours with little control over the result. Even the approaches in well known books are inadequate.
As far as nm of Ha I was under the impression smaller nm was better as less "other" light gets in. Downside was longer exposure times but more detail when you did. For example Fred's 3nm Ha images which show detail not seen in other Ha images. Also Don Goldman's 3nm Ha images of Helix etc show detail not seen before. But it was hard work I believe.
I use an Astrodon 5nm Ha and I think its very nice indeed.
Not sure if using a 40D makes a difference in that regard, I am talking about CCD cameras. Don't see what difference it makes though.
Even with 5nm Ha I find I get nicer contrast when no moon compared to moon although the results are still very good with a moon.
Greg.
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