Click to expand.

The Trapezium is seen at the center of M42.

Gadgets:
Sigma Telephoto lens 150-500mm at 500mm FL,
with two EOSs, EOS Rebel XSI and T3, both modded,
0.5,2,4,8 minute exposures (4~8 frames each) at ISO1600 with XSI and Orion SkyGlow filter and,
2 min. x 25 frames at ISO3200 with EOS Rebel T3 with IDAS LPF P2,
4~8 darks and 20 flats for XSI and 20 darks and flats for each for T3.
Note 8 minutes frames were discarded due to drift.
The processing was not easy due to the difference in the transmission spectra between the Orion and the IDAS filters.
Layer Mask method with Photoshop CS5 was used to composite the images.

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H-alpha and RGB composite for the M42/NGC1977 image
The shots were made just for testing purpose!
(1) 2 min. x 3 frames (IDAS only)
(2) 3 min. x 8 frames at ISO3200 for H-alpha (poorman’s H-alpha — Lumicon H-alpha + IDAS LPF P2)

same Sigma zoom lens (150-500mm) at 500mm FL.
Regardng the H-alpha and RGB composite, please refer to the URL below about the method of 80/20/20 by Neil Heacock:
http://tinyurl.com/7jqxzly

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The following shows the images (1), (2) and the composite.