I spent some time looking at your images, I totally love them. They're amazing! The Elephant trunk is one of my favorites.
By the way, you asked me about Startools the other day, and Ivo, the guy who wrote StarTools decided to process my Heart nebula to show me what the tool can do, and I was blow away for an image that is taken from a Bortle 8 sky like Portland downtown...I uploaded his processing and obviously gave him credit for that, and I thought you may want to take a look to it.
Thanks for the comments Marc. The Canon 20Da has 2 main features for astrophotography, it has a slightly better IR response and more important it has 2 live focus modes that enlarge the center of the image making focus very easy. Trying to look through the view find is useless for the sky. My understanding is that when the 20D was in production one of the big executives asked engineering to make ans astronomy camera for him. They said they could not make one but they could make 5000, so they did and sold them. Don't know if this story is true or not.
True, you can set Grad Xterminater to deal with sudden changes via the "Fine" mode and "Strong" corrections, but I suspect that such a harsh filter would alter other desirable detail in the image(s).
Part of the issue with gradients is that one side of one of the images you are merging could have a brighter overall level than the other image you are merging, yet on the other side of the seam you could very well see the opposite in brightness comparisons. So when you got to equalize things on one end of the seam, you actually make things worse on the other end of the seam.
And from what I have found, it takes just a tiny tiny difference in levels to produce a visible seam....so this is a really 'picky' process (which I am still not 100% confident with doing!)
Hi Marc. That's a good question, and one that's relevant to ccd imagers too, because sky conditions vary so much during a night, or from one night to the next.
From what I have found, you will see some difference in the backgrounds, although some NoiseNinja or other noise removal routine will help. What you will end up having to do is to equalize the backgrounds while blending, and this MAY limit some of the faintest stuff you got in the image with the least noise. But it shouldn't be huge difference.
I should mention that the most pressing issue when blending images was that you have to do a careful job of flat-fielding and also removing any gradients due to the influence of light pollution or the Moon. The program Gradient Xterminator is excellent at this, If you don't have a perfectly flat background, you will blend on part of the overlap well, but then find that another area where the images overlap has a visible seam, and if you correct the visible seam, then the first area may not blend properly.
I hope this helps Marc. I look forward to seeing the results of your two-panel mosaic! :-)
Thanks for the comment Marc. I just went through your album and you have some very impressive shots. That particular shot of M76 was 9 5Min exposures on my 14" with a 12nm Astrodon filter. I also have the 3nm Astrodon and it would have brought it out more with less stars shine but I am setting out to get all Messiers in my backyard with Ha and since most are stars the 12nm gives me better overall results. I see no reason why your equipment wouldn't give you the same results. From my home location in So. Cal. narrowband filters have been a god send.