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Another image of one of the most popular objects imaged by astroimagers... The Horsehead Nebula/Barnard 33 with Alnitak and the Flame Nebula, but exposed mainly through narrowband filters, but emulating natural colors of the object.

I was planning to combine H-Alpha as red, OIII as green and H-Beta as blue channels to create a natural colour image through CCD narrowband filters, eliminating any light pollution or moon sky-glow in the process.
Unfortunately, the last night when I was able to do any imaging of subs for this object was on the 20th February before it became cloudy every day and night with constant rain.
Having already completed the capture H-Alpha and RGB data, I set my exposure plan to alternate between OIII and H-Beta subs during that night, which is lucky because I only had a short window of a few hours and it turned out to be my final night of imaging for the foreseeable future. I managed to get only 3 x 30 minute H-Beta and 4 x 20 minute OIII narrowband subs.

After waiting for a couple of weeks, I figured that I'm not going to get much decent time on Barnard 33 before it become obscured by landmarks so I decided to combine my currently exposed subs, H-Alpha into red, OIII into green and H-Beta into blue, as planned, and added 25% intensity from my RGB subs resulting in the image above.

This image total exposure time was 9 hours and 32 minutes, channels consisting of 15 x 600 second H-Alpha, 4 x 1200 second OIII and 3 x 1800 second H-Beta 7nm narrowband subs with only 25% intensity added from the 14 subs each through red (180s), green (300s) and blue (600s) filters.

Taken through a 80mm Refractor @ f6.25, on a hypertuned CGEM mount with QHY268M camera.

I think that my narrowband imaging imitating natural color experiment is (once again) successful... the first time I tried this filter to channel alignment was on the Trifid nebula last August.

The advantages of exposing images through this narrowband filter to channel alignment is that most of (if not all) light pollution is rejected, imaging is possible during moon light (within reason), colors look natural, I find that more detail is captured through narrowband compared to broadband filters and narrowband filtered subs are much less susceptible to lens flares and/or internal reflections when there are bright stars near by to the object.

The only disadvantage I can think of is that the subs exposure times are a lot longer, resulting in much longer total exposure times needed for each image... although I'm starting to doubt this fact now after seeing how clean my H-Beta and OIII stack ended up being when they were stacks of only 3 and 4 subs... perhaps shorter exposure time per channel will suffice?


© Mariusz Goralski
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