Jim,
Very nice images. I particularly like the vibrant colour.
It's a shame you have a little trailing and that the M20 shot doesn't seem quite as sharply focused as the others, but they are still very good images.
You say guided with an ED80 - was that using a camera for autoguiding or manual guilding by you using an eyepiece & correcting for errors?
Regarding the dark frames - I believe it to be quite 'normal' to take several dark frames than just one. Usually I'll take a series of 10. I examine them individually to make sure there's nothing abnormal about any of them - sometimes spikes of brightness will appear randomnly that are not consistent between the dark frames and I don't want those incorrectly being subtracted from the final image.
I'm not good with technical terminology and all that, so my rather simplistic view of why the several DF's make a better result is simply the same as why several light frames make a better result - improving the signal to noise ratio, where in this case the signal is the noise we want and the noise is the random occasional noise that we don't want to subtract.
Does your software cater for subtracing BIAS and Flat frames also? They would of course be another step in helping, and the reason I think of them is because as with dark frames, I would shoot 10 of each and average them out.
I wish my un-modified 350D could get that nice colourful nebulosity
Roger.
