Paul - Simply not the case at all..
10 minutes will over expose the core, but you still wont get the deep dusty areas surrounding M42 in less than a 15 minute exposure..
The way to go with M42 is lots of subs, at many different exposure levels..
My best M42 to date consisted of:
10x10sec Ha subs
6x30sec Ha subs
8x10min Ha subs
17x4min colour subs
40x10sec color subs
Each of these sets of subs were stacked separately, giving me 5 .tif images. I then input the 5 tiff images into Registar, which countered the rotation and offset of each of the 5 resulting images, and saved the 5 new .tif files
Using photo shop I processed each of the tif files individually to its own merit (Very gentle stretching on the shorter subs, to retain the cores detail and the trapezium, and rather agressive stretching on the longer subs to bring out the fainter whisps of nebulosity that are not commonly seen..)
Still in photo shop, I layered the 30sec Ha tiff with the 10 min Ha tiff to create the final Ha image. which after layering, was evenly exposed from the very faint whispy details surrounding M42, right the way through to the 4 stars in the trapezium.
I then layered the colour Tif files together, creating an evenly exposed colour image.
Finally I layered the Ha image (black and white) into the final colour image as a luminance layer.. The Ha data showed much more fine detail than the colour one, due to its longer exposures, and hence forth, using it as a luminance was the best way to get the faint details to stand out in such short colour exposures.
Generally speaking, the longer the exposure time, the better the final image.. and the best exposure time for 90% of targets is the longest exposure time your setup can do before tracking errors occour..
M42 is a deceptive target.. because its big and bright, many people begin to thing that its an easy target to image... Whilst it is very easy to capture nebulosity in this area due to its brightness, it can be VERY difficult indeed to take an image of m42 that is great. This is due to its incredibly varying dynamic range... It contains everything from very dark dim areas of dust to extravagantly bright emission nebula.. Thanks to its composition, it is nessacary to take many sets of data at varying sub duration in order to give your image the depth required to show off everything this stunning target has to offer...
There are some images I've seen of M42 that have MASSIVE data sets.. the best I've seen had 50x5sec, 50x10sec, 50x30sec, 20x60sec, 10x3min, 10x5min, 10x10min and 10x25min...
That is one hell of a task just to capture that sort of data.. then to process it all... Its not for the faint hearted...
You've done well in your attempt, and Im sure you will improve on this in the coming months!
M42 is all in the processing... Capturing data is easy, Processing it to get a good result is very difficult.
Keep at it mate, and keep those exposures long!!
