This was over 9 hours of RGB data. At the time I was just glad to see the nebula itself in a single frame, but the time I stacked it, all the background stars and chromatic aberration of the old lens rendered the nebula virtually invisible.
Undaunted, I set out to improve upon this image. I picked up an optolong l-enhance filter at roughly 5X the cost of the whole lens. Suddenly the nebula stood out strong against a dim background of stars. But another 9 hours of subs left some great OIII data, but after learning to use the “extract H-a” and OIII debayer algorithms in APP, the OIII data looked great, but the H-a data was complete mush.
I set out with the theory that the lens wasn’t able to focus the two wavelengths at the same point, so I scribed a scale on the lens, and the next clear night I adjusted focus and took test shots, and used the FWHM measurement in APP along with the “extract H-a” option to find out which focus position resulted in the lowest FWHM for the H-a band pass. Success! I could get sharp H-a data at the expense of the OIII band pass. Unfortunately my dew heater failed that night, and I only ended up with about 2 hours of H-a data.
Anyways, this image is my attempt at putting lipstick on a pig. Because of the poor SNR of the H-a data, I couldn’t make a decent HaORGB image. So this is the result of the following:
Stack the RGB and the H-a and OIII data separately. Use starnet++ to remove the stars from each channel.
Since the OIII stars were the smallest, use the stars-only image of the OIII stars as a mask for the RGB stars to remove the CA.
Start with the star-removed RGB image with the lowest noise in the background. Due to the huge number of large stars, the background was splotchy so apply lots of noise reduction.
With an inverse luminance mask, blend the sharp HOO nebula data (with stars) into the noise reduced RGB data.
Add back the focused RGB stars. Lower the opacity to 10% with the “lighten” blending mode in GIMP. Since the sharp HOO image still had stars (starnet++ made mush of it when the stars were removed), this blended the nebula with a reduced star field.
Add another copy of the RGB stars with the “erode” filter applied, but blended at 100% opacity to bring back the brightest stars.
Adjust levels/curves/saturation, etc.
This final image isn’t great, but made me learn a lot about post processing. Bracken’s book made for great instruction. Anyways, maybe it’s a bit of an improvement? Suggestions for how I can do this are more than welcome.
All this because of bad optics...