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Hi Paul,
You are being a bit hard on yourself that is a good result for learning new gear.
A couple of critiques:
1. Framing. To my eye it would be better to have M42 at that angle a bit more over to the right. That way the extended nebulosity will flow into the diagonal of the image. This image doesn't show that extended nebulosity but it could have. So if it did the image would have been off balance framing-wise. I usually look at someone elses image to frame the object before I do anything.
2. 25 minutes. Not sure what that means - one exposure of 25 minutes or several at 2.5? I suggest you use a standard exposure length for your camera/scope/mount. The shorter the exposure the easier on tracking but the less you will get of faint details. I use 10 minutes. I used to use 15 minutes. You have to get the signal above the noises of the camera to show anything. As pointed out there is an exposure calculator for different CCDs. 10 minutes is a handy length though.
3. M42 needs a unique approach because the core is so bright. You take a long exposure image of say 2 hours worth of LRGB at 10 minutes each.
Then you take a core shot of LRGB at about 15-30 seconds each. The core details are usually burnt out above 30 seconds but check it for your system and camera by test. Otherwise just take say 5 or more runs of LRGB at 15 and 30.
Then you process each shot separately then you replace the burnt out core of the long exposure with the shorter exposure core shot you took and blend the 2 to hide the join. There are a few ways to do this. There are examples on the net if you google it.
4. Sharpening is best done by selective sharpening. I almost never use
unsharp mask. Its like a blunt instrument that is too harsh very easily.
Again google selective sharpening. There are free tutorials. I think Don Wade has some on that. It basically consists of making a duplicate layer, setting it to overlay, run high pass filter to suit (perhaps 4 or 5 pixels),
layer/mask/hide all, set the background/foreground tool in the tool box to white/black now rub with the brush on the areas you want to come through in the underlying sharpened image and not areas you don't.
You can reverse the foreground/background to cover up areas you accidentally rubbed on (eg stars can look overly sharpened).
When finished layers/flatten image.
Seems like you got a lot of things right though in that image, cooling, autoguiding wasn't too bad, callibration etc.
Greg.
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