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This has been on my hard drive for some months, so nice to have finally got round to processing it! Shot over several nights in January in my back garden.
NGC 281, also known casually as the Pacman Nebula, is a bright emission nebula and part of an H II region in the northern constellation of Cassiopeia and is part of the Milky Way's Perseus Spiral Arm. It lies about 9,500 light years from us and is 48 light years across.
As the final version, I've gone for a crop, which I think holds up well, though I'll include the wider fov version in the next post.
I used a more natural colour blend for this image:
R = 76%*Ha + 24%*SII
G = 100%*OIII
B = 85%*OIII + 15%*Ha
For some reason, I was not expecting much from this image, but the result looks like it will be one of my favourites...the narrowband data was really good!
Captured using APT, stacked using APP and processed in Pixinsight.
5.4 hours integration time.
Link to full details and higher res version.
Thanks for looking!
So we had a completely clear night last Thursday and, as luck would have it, i was actually off work all week, so i was able to take full advantage. Well, mostly, as you'll soon find out.
As it turned out this was a night that almost went completely awry. The first thing that i messed up was i forgot the external battery that keeps the D5300 powered all night. I only noticed this after driving the 45 min trip back to the family home where i do my imaging. Doh! Luckily though, i dipped into my big bag of astro stuff and found the 2 old camera batteries and charger that i used to use. By my reckoning it was last December when i last used them, so i was amazed to find they still had quite a bit of charge in them! So i was able to charge one while i used the other. Unfortunately though it meant i had to keep going out to the scope every 2-3 hrs to change battery, but tbh i was just relieved that i didn't have to drive home and lose another 90 mins of dark sky time.
The next thing to grumble was the guider. For some bizarre reason, i could not see Polaris in the Fov in Sharpcap. I could barely see anything at all tbh so even though Sharpcap told me it was able to platesolve i was very dubious. And then when i came to do the Sharpcap PA routine, the adjustments were jumping around all over the place. It took me about 25 mins to PA instead of the usual 5, and i really thought the guiding was going to be a nightmare, but what do you know, it turned out to be actually really good. It even dipped below 0.5" at times. Go figure!
Due to the floodlights of the sports facility (which is rather conveniently only about 100 yards away from the house) i was forced to start with Ha subs, then once they were turned off at 10pm, i switched to Oiii, as i knew the moon was coming up around 00:30 so i needed to take advantage of the darkest part of the night. I figured i'd go for about 3 hrs of Oiii, knowing that with the final filter change back to Ha again, i should end up with about 4-5 hrs of Ha in total. Well, after doing the last filter change and going back in to grab a nap for a couple of hrs, when i woke up and checked Team Viewer i noticed that the sequence had unexpectedly ended. Went out and saw that the 7 Ahr LifePo4 battery i use for the mount had died. I also noticed that the lens of the Finder-Guider had completely dewed up. As it turned out, the dew strip for it had failed so i've had to order a new one. I've also ordered a PSU to power the HEQ5-Pro from the mains, so fingers crossed i shouldn't have to worry about mount power over the winter now. All in all this was a bit of a pain of a night, as i normally only shoot 1 filter per night. Sometimes in the longer winter nights i might do 2, but i've never done 3 before. It's a real hassle too, as i need to shoot flats, change filter, re-frame and re-focus. All of which can take upwards of 30 mins. Hmmphh.
So long story short i didn't end up with as much Ha as i wanted for this, which has meant it's been trickier to process than i would have liked. I should probably have just waited and done another night of Ha, but with all the hassle i have to go through to get any imaging done these days (drive, setup, tear down and pack away, drive home, sleep deprivation) i will always just try and use what i've got and move on to the next target. The Mean ADU level was quite low on this one, probably because the target is quite small and only occupies the centre of the frame. I've probably been lucky up to now, by mostly shooting larger targets, so i was disappointed with the low ADU levels, which are scraping the bottom of the barrel for me in terms of getting away from the noise floor. So i upped my exposures a bit, pushing as high as 25 mins, which is the nighest i've ever gone with the HEQ5-Pro. It seemed to still handle it quite well, although it didn't improve the Mean ADU level anywhere near enough.
Full capture details:
3 x 1200s, 2 x 1380s, and 4 x 1500s of Ha
9 x 1200s of Oiii.
11 x 480s of RGB (with an IDAS-D1). Used for the stars and sky background only.
7 Hrs 54 Mins in Total.
All shot with a Nikon D5300, SW 80ED, and an HEQ5-Pro.
The RGB data was shot over a year ago from inner city Belfast (Red Zone) while i was testing out the new Rowan belt mod. It was just a test shot to check the guiding, so the 8 min subs were far, far too long in reality, hence a lot of the medium and bright stars are clipped. But i have to say, the IDAS-D1 together with APP did a nice job of cleaning it right up and making it at least useable (well, by my standards at least!).
So on to processing. I've been playing with this for several nights now, and i just can't look at it anymore! i think this is the best i can manage with the limited data i have. It's been enjoyable and yet frustrating at the same time, lol. As usual, this has been stacked in APP and processed in PS. I used the tone-mapping method of processing, and created a synthesised Sii from a 50/50 blend of the Ha and Oiii. I then combined them in the classic Hubble Palette SHO. Obviously, not having any real Sii means i can never get the full range of tonal variations throughout. I'm also not completely happy with the colours if i'm being honest (especially the blue). That was the part i struggled with the most on this one.
I've also attached below a quick and dirty HaRGB version, which took me all of about 30 mins to process (in total contrast to the SHO version, which i won't say how long it took!).
As always, constructive criticism welcomed with open arms!
Ok time for me to stop rambling on now ?
Edit - Forgot to say, I resized the sSHO version down to 75% of the original (it's not worthy of 100% viewing).