M42 is tricky, even for the best imagers due to the fact that to get the outside nebula, so to speak one has to expose longer, and then the center gets burnt out.
Many people take a number of exposures at different exposure lengths, and then combine all of these different exposures in PS2 for instance.
One would take say, 10 at 15 seconds to get the core, than some at 1 minute to get the surrounding nebulas, and so on.
They would then combine all of these images, and manipulate them in PS2, or similar software to get the correct levels need to make it all come together.
I am no expert at this but others here will surly advise you further.
However you first attempt is excellent I might add, and you are on the right track.
I do feel that you should keep your ISO at about 400, 800 and 1600 is just to high for this object.
I image at 400 regardless of what I am shooting for, and just lengthen the exposure to suit.
Hope this helps a little bit.
Leon
