This is a widefield mosaic and HDR, including;

• M42 - Orion Nebula
• NGC 2024 - Flame Nebula
• IC434 - Horsehead Nebula

Capturing
I used the Askar FRA300 for a flat field and wide view. My current setup with the ZWO 2600 DUO and AM3 is extremely mobile and fast.

As the latest Firmware from ZWO included finally increased FWC with GAIN -25, I used this option with 3-sec exposures to take the first round of the 2x2 mosaic. The idea was to get the most dynamic aus of Orion`s trapezium, which worked very well. With this short exposure, I took about 40 frames per mosaic piece.

Afterward, I took about 20x 180-sec exposers per panel with GAIN 100 to get more faint details of the region. I would have preferred to take more shots, but the night was moving on fast, and with it, Orion was moving closer and closer towards the horizon. 

Processing - APP
I started with stacking each individual panel with Astro Pixel Processor, my personal choice for stacking and mosaic stitching. I did this for the first four panels with the GAIN -25 setting and the same for the last four panels with GAIN-100. Afterward, I dynamic-cropped each frame in Pixinsight. I progressed every single one in GraXpert to remove the gradient/light pollution, which was introduced by the low altitude close to the horizon. Then, I stitched the first four panels, followed by the second two.

Processing - Pixinsight
Within PI, I used one of my preferred workflows to progress the pictures. Color Calibration, Deconvolution, Stretching, Curves.... you name it. I worked on the clouds and stars separately and saved the final outcome in three files.

1. GAIN 100 - Stars
2. GAIN 100 - Nebulae
3. GAIN -25 - Nebulae

Processing - Photoshop
After loading all three images into PS, I made some final adjustments with the Nebulea layers by using the "Camera RAW" Filter. In my opinion, the easiest, fastest, and most comprehensive solution to quick-fix the final look. I added the high-dynamic Orion into the Nebulea background, which can be considered a form of HDR. It is actually not HRD throughout the whole frame, but especially for the Orion region. Adding the stars with negative multiplies reduces the opacity of the star layer to 80-90% for more highlights on the nebulae. 

After uploading the picture to Astro-Bin, I noticed a green cast the the picture. Therefore I run SCNR within Pixinsight for the very final last touch.