4000 light-years from Earth lies The Butterfly Nebula (IC1318), part of the much larger Sadr Region in central Cygnus. This photo spans 80 light-years, but the area it occupies in the sky is only twice the size of your thumbnail held out at arm’s length.
Askar 130PHQ: August 2023
Cygnus is high overhead as seen from the UK this time of year, and it’s full of intricate nebulae. My Askar 130PHQ telescope has a focal length of 1000mm, which means it’s well suited for tight framing, detail-oriented shots. For this project I chose The Butterfly Nebula (not to be confused by a planetary nebula with the same name) because it looked interesting and would entirely fill the frame edge-to-edge.
As is now my standard practice for these types of nebulae, I used an Optolong L-Ultimate filter for H-alpha and OIII data; an Askar D2 filter for SII and more OIII; and then no filter just for the stars, to give them fairly accurate colours. So it’s an SHO image from an OSC camera. In terms of integration times, the L-Ultimate is 15 hours; D2 is 20 hours; and the no filter RGB stars is just 30 minutes (stars are really bright so you don’t need much time on them).
I’m receiving a lot of requests for a processing guide for this approach, and I plan to make one soon. Meanwhile, I made what I think is an interesting comparison of the data sources. I took just the Optolong L-Ultimate data and made a rough edit, producing a starless image. Then I did the same thing with the Askar D2. You can compare them using the slider:
The L-Ultimate data is better quality despite the lower integration time, simply because there’s so my H-alpha in the nebula. But the D2 is clearly bringing a different wavelength into the mix. My final image is the result of mixing L-Ultimate and D2 data, with RGB stars sprinkled in top.
There are methods of creating pseudo-SHO images from just the stronger Ha/OIII data. Perhaps best-known nowadays is the Bill Blanshan Pixinsight script that does this with a single click. For interest, I ran this script on my L-Ultimate data and gave it a very quick edit:
I much prefer the version with Askar D2 data added, although admittedly it’s a far longer total exposure time and was more fiddly to process.
Imaging details
* 19 July – 24 August 2023 (five weeks)
* Bristol, UK (Bortle 8)
* Telescope: Askar 130PHQ Flatfield Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Mount: Sky-Watcher EQ6-R PRO
* Guide: William Optics 50mm Guidescope with 1.25″ RotoLock; ZWO ASI 120MM Mini
* Control: ASIAIR Plus
* Software: PixInsight, Lightroom
* Filters:
– Optolong L-Ultimate (Ha / OIII): 450 x 120 seconds (15 hours)
– Askar Colour Magic D2 (SII / OIII) : 600 x 120 seconds (20 hours)
– No filter (for RGB stars): 15 x 120 seconds (30 mins)
Total exposure time: 35.5 hours
By Lee Pullen
Example source data
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