The Orion Nebula has a very wide brightness range, so you have to take sets of subs at different exposures. Long exposures for the faint outer cloud and short ones (just a few seconds) for the trap and bright core. They are then combined with masks, layers or feathered selections in a program like photoshop.
There's tutorials on the net. One here, but there are many ways to do it.
http://www.astropix.com/HTML/J_DIGIT/LAYMASK.HTM