Tutorial
This section decsribes the processing steps I made when processing the raw images of M82 taken at f10. I made 10 exposures of 10 minutes each at 1600x1200 resolution for the Luminance layer. For RGB I made 6 images of 5 minutes each at 2x2 binning. For each of the resolututions I made darkframes in the given resolution at the corresponding exposure times.
The darkframe is shown in Figure 1 and the flatfield in Figure 2. These are images correspronding to the 10 minute Luminance exposures. The flatfield images are taken with the Lightbox I made myself. A pictures of this box can be found in the Equipment section. It's important to take these images during the imaging section itself after carefully focussing. I take the images outside after the imaging session without changing focus. If you change focus you need to take ne flatfields. I set the exposure times such that pixel values are half of the maximum values. For my ST2000XM this is around 32000. Setting exposure times such that the image will have a maximum pixel value between 24000 and 32000 works fine.
I use MaximDL to load the original images and adjust them using these flatfields and darkframes. I Normally take about 3 to 5 flatfields or darkframes and use the "average" function in MaximDL when correcting the source images. The result of this adjustment is show in Figure 4 when applied to a raw image as shown in Figure 3. Especially the effect of applying a flatfield is tremendous. After this calibration I use the align feature of MaximDL to align all images and created a summed image of all source images. This summed image (shown in Figure 5) is then loaded in Photoshop using the FITS Liberator. This is a very usefull tool developed by ESA/ESO/NASA which will help you to load Fits images in Photoshop and to process them in an easy way. Check out the Links section to download this free software plugin yourself. The result is shown in Figure 6. 
After applying the FITS liberator you can use the standard levels, curves and filters in Photoshop as you would do normally. In the same way the RGB images are processed. After creating the summed images these are aligned with the luminance image to ensure that they will overlay correctly when creating the LRGB image in Photoshop in the final step. The RGB images are shown in Figures 7,8 and 9. The red, green and blue images are converted into a single color image using the "merge channels" function of Photoshop (Figure 10). Finally the color image is resized from 800x600 pixels (2x2 binning) to the resolution of the Luminance image (1600x1200 pixels, 1x1 binning).
The color image is then pasted as color layer in the luminance images resulting in the final image as shown in Figure 11.
