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NGC7822, including Sharpless 2-171, a.k.a Cederblad 214 in Cepheus.
This luminance channel for this image is the stack of 12 eight-minute exposures taken through an Hα filter,
shown below.
While shooting the color data I was plagued with clouds, and was only able to
save 5 reds, 6 greens and 4 blues at 8 minutes each.
I threw away the red data and used the Hα for the red.
I added the green images and the blue images together,
and used the result for both the green and the blue channels.
I then sigmoid stretched the Ha and used it as the luminance.
This worked because the red data from the nebula is all from the
Ha emission. The blue-green is all from the OIII. So treating the
filtered data this way gives you a pretty reasonable color rendition.
Only the star colors suffer, because stars are broadband emitters,
unlike nebulae, which are emission line objects. A little bit of the
AIP4Win Star Color Tool fixed that up quite nicely.
All images were acquired using an STL11000M CCD camera on a Tele Vue NP101is.
The exposures were calibrated, defect-corrected, stacked and color-combined using AIP4WIN V2.
This image has been resampled down from its original size of 4008x2672.
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