I captured 15 hours of data on the bubble nebula between Sept 5-6th, 2020. the target is small in the field of view with my telescope focal length and imaging chip combination, but thought it might be interesting because of the unique structure of the nebula. The nebula is heavy in the Ha range of the spectrum, but also has a clear Oiii component to the bubble itself. the imaging session details are below:
| imaging camera | ZWO ASI 1600MM Pro |
| guide camera | ZWO ASI290mm Mini |
| mount | Skywatcher EQ6-R pro |
| telescope | Explore Scientific ED102 APO |
| exposure settings | for all filters: gain 139 exposure 180s |
| filters | Optolong 7nm Ha Optolong 6.5nm Sii Optolong 6.5nm Oiii |
| stacking | 100 Ha lights 105 Sii lights 100 Oiii lights additional calibration for each channel 30 darks 30 flats 30 dark flats |
| processing | PixInsight |
Here are the three channels to compare the underlying data. Each image is stacked, cropped, and has dynamic background extraction a stretch applied.
ngc 7635 bubble nebula – Ha data 
ngc 7635 bubble nebula – Oiii data 
ngc 7635 bubble nebula – Sii data
I was initially stuck with a very green image when I combined to RGB using pixel math. the normal approach of using curves or scnr to reduce the green just wasn’t working to leave much to work with. I did a bunch of trial and error with curves to arrive at the following image:
I also created a starless image of this one again just for comparison purposes:
