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Confusing Results - OSC - Adding Ha to RGB data.

Processing Deep Sky NGC3034 M82 Galaxy
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Craig Dixon avatar
Craig Dixon avatar
I decided that M82 (Cigar Galaxy) would be a great target to try combining RGB data from a OSC camera with DNB data (Also OSC) but the results I got have left me confused. I assumed the best way to image this target would be to shoot the galaxy with a UV/IR Cut filter and then again with a DNB filter. Then split the channels from the DNB and add the red to the UV/IR data. Here's the data I collected:

6 hours of 300 second exposures with the Astronomic L3 filter
12 hours of 300 second exposures with the Optolong L-enhance
1 hour of 20 second exposures with the Astronomic L3 just for the stars

I stacked and processed the data so many different ways and the final result I decided to publish is here:

https://www.astrobin.com/5pscfd/

This data set includes just the 12 hours of L-enhance data (and then the 20 second subs for the stars) as the full data set I processed just didn't look as good.

Here is a screenshot showing three different versions:

The left image is the 12 hours of L-enhance data only
The right image is the 6 hours of Astronomic L3 data only
The middle image is the two data sets combined using the NBRGB Pixinsight script

I'm pleased with the final result I published but it has me wondering about whether I'm using the correct filters. My understanding was that the Astronomic L3 should be used for broadband targets and the L-enhance for emission nebulae. I've processed all of the versions to the best of my current ability but there will naturally be slight variances due to my processing. Throughout the whole process, I didn't find the combined data set to contain any more information than just the L-enhance data.

Is anyone able to shed any light on this? With so few clear nights, it's important for me to make the most of the imaging time I do get so I'm keen to fully understand these filters.
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andrea tasselli avatar
andrea tasselli avatar
If I were you I would have used the DNB filter all the time and added just the RGB stars at the end. Given that you did not do that and you have a 6-hours worth of RGB data a different approach is needed. In my similar attempt (here:M82 NB-RGB (OSC) - The Cigar Galaxy ( andrea tasselli ) - AstroBin ) I opted to combine the two data sets (L-Pro and L-Extreme in my case) using pixel math in Pi, after re-normalizing the two data sets (and removing the stars) as the most effective way of adding the H-alpha data into the RGB sets. I think I iterated the process 3 times to get the right mixture of streams visibility and galaxy main body depth.
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Craig Dixon avatar
Craig Dixon avatar
andrea tasselli:
If I were you I would have used the DNB filter all the time and added just the RGB stars at the end. Given that you did not do that and you have a 6-hours worth of RGB data a different approach is needed. In my similar attempt (here:M82 NB-RGB (OSC) - The Cigar Galaxy ( andrea tasselli ) - AstroBin ) I opted to combine the two data sets (L-Pro and L-Extreme in my case) using pixel math in Pi, after re-normalizing the two data sets (and removing the stars) as the most effective way of adding the H-alpha data into the RGB sets. I think I iterated the process 3 times to get the right mixture of streams visibility and galaxy main body depth.

Thanks. I gathered more DNB data than broadband after you suggested doing so on a different post and am glad I did so thanks for that.

I tried a few pixel math methods but just couldn't get it right. Adding the Ha data to the red channel just left a deep red cast over the entire image.

I'm pleased with the final image and it got top pick nominated, which is encouraging but it has just left me wondering about the best times to use the filters. The results here were just unexpected.