Imaging The Pleiades

For my partner Amanda, who fell in love with it the moment she saw it through the viewfinder.

To astrophotographers the Pleiades, or Messier 45, need no introduction. It’s one of the naked eye deep space objects (DSO) that we cut our teeth on. Which is funny because, as bright as they are, and tantalisingly easy to shoot, they’re actually difficult to get right. But even done wrong they can be pretty spectacular.

The Pleiades (/ˈpliː.əˌdiːz, ˈpleɪ-, ˈplaɪ-/),[7][8] also known as The Seven Sisters and Messier 45, is an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. It is among the star clusters nearest to Earth at approximately 447 light years distance, it is the nearest Messier object to Earth, and is the cluster most obvious to the naked eye  – Source Wikipedia.

The Legends

There are a great many legends that revolve around the Pleiades, more than I have the time and space to go into here, but it seems that throughout the ages of humanity, it has had tremendous significance, culturally, astronomically and socially. Most are similar with regards to the names and numbers of visible stars, although there are some variations. Perhaps my favourite version is of the Pleiades being the daughters of an Amazonian queen, and who were acknowledged to be the creators of ritual dances and nighttime festivals. Although perhaps the most famous of the legends stem from Greek and Japanese ancient literature. In all honesty there are so many different variations of the legends surrounding the Pleiades that you could spend an eternity researching them all.

Previously…

The last time I imaged the Pleiades was about two years ago when I managed to grab about 5.5 hours using the modded Canon 450D on the SkyWatcher 72ED.

Previously…

It’s not a bad image, but with it being such a bright broadband target, using the modded camera was pretty much a waste of time, although I don’t think it really did it any harm. My processing however, left a lot to be desired, and I wasn’t shooting calibration frames at the time either, so the image has suffered for that.

This time out I wanted to sink a lot more integration, or exposure time, into it using a “stock” DSLR, the Canon 60D. And this time I’m going to be using the “big rig”, the EQ5 Pro to push for those longer exposures and bring out more detail in the surrounding nebula.

1st Night

It’s been that long since I used a GoTo mount that it quite literally took me 3 hours plus to setup and iron out the bugs. I know why though, it’s because I rushed the setup after getting home from work. I didn’t secure the spreader plate properly, I didn’t seat the mount on the tripod properly, I didn’t lock off the alt-az adjustment screws. But piece by piece I got it there. So tonight the new mount, the replacement EQ5 Pro (after the last one fell off the decking) finally gets its first light…it’s only been 465 million years!!

But for a first light and rushed setup, although it’s hard to not get hung up on the guide graph and numbers too much, it’s REALLY nice to see such good ones…

With a total RMS of consistently less than 0.5 I’m loving the new mount. And after spending several hours freezing it’s nice to get indoors and remote it via TeamViewer.

Looking at the single frame from APT, I don’t think going for the longer frames is actually a good idea. Even in the one frame you can see some of that nebulosity, and that’s just 60 seconds at ISO 800. Whereas with my original image, the stars were pretty bloated due to the removal of the IR/UV filter on the 450D, the 60D doesn’t suffer from it, and keeping the exposure to 60s is definitely the way to go.

75 mins in class 4 skies at home with the stock 60D. Totally blown away by this already. To my eyes, it already looks better than the 5.5 hours of my original image.

Of course it’s helped by the fact I’m imagining in class 4 skies this time as well, as opposed to the class 5 on my first attempt. Okay, so it’s a difference of just one number, but that one number makes a big difference when imaging deep space objects, even a bright one like the Pleiades. You’re not fighting the light pollution, and you can run without having to use a city light suppression (CLS) filter, so you also don’t get any of the haloes around the brighter stars either. All of this adds up to making the processing that much easier too, and you don’t have to be so aggressive on stretching the data.

The version above has been stretched considerably, but that’s purely down to only having 75 mins of total exposure time. As my time on target increases so my aggressiveness with the data will decrease, which will translate to a smoother finished look AND more detail in the nebulosity and surround dust cloud.

2nd Night

My second outing on this took place over a month later due to, you guessed it, our abysmal British weather.

Right from the outset I was up against it. Although the forecast said otherwise, I was blessed with some clear skies for a few hours, but with gusting winds and a mount that was refusing to guide in DEC and only allowing me to track in RA, I was having to nursemaid it through every frame almost, and on several occasions had a “hard stop” reported in APT for the camera, which required a disconnect of it and starting the imaging plan all over again. Thankfully it still retained the images that I’d captured though so it wasn’t a complete loss, merely frustrating.

The guiding issue I’m at a loss over, because when I first tested the rig I was getting 5 minute subs with no difficulty. I do have a theory though, and that is that the power supply I’m using is either failing or not up to the task, despite it being mains powered. So on the next run out I’ll try swapping it and seeing what happens.

In all from the second night I managed another almost hour of usable data, bringing the total acquisition time up to a solid 2 hours in all.

Stacking and processing what I had at this point was a slow task, but the end result so far was worth it. The detail that was coming through was pretty nice and I was seeing some nice separation between stars now, with reduced haloing and greater nebulosity. And already, I’m not needing to be so aggressive with the data stretch.

UPDATE Separate night imaging M81 and M82 and I’ve swapped the power supply. It seems that’s definitely solved part of the issue and I’m guiding, at least in RA, with 2 min subs, although not on this target. DEC still goes off and does its own thing though. I’m also going to switch back to “on camera” guiding and see if that helps.

2hrs (120 x 60 sec) at ISO 800

Pixel peeping this I quite obviously need a field flattener (look out towards the corners and you’ll see quite clearly elongated stars), and eventually this is something I’ll get a hold of. But, all other things being equal, I’m pretty happy with what I have so far.

3rd Night

Approximately 6 weeks later…that’s roughly how long it’s been since I last imaged at home due to, yup you guessed it, the weather. Its been pretty dire, even for the UK, but tonight is the first of two forecast clear nights.

My boss, bless him, allowed me to finish work two hours early, purely so that I could set up without rushing it in order to maximise imaging time. I’ve managed to capture a further 3 hours of usable data from tonight, which looking at the moon state, may well be my last run of the season on M45 from the back garden, unless I’m able to go portable. We’ll see. In total that now brings me up to a total 5hrs in all.

Two rigs running tonight at home. The main is on M45, whilst the Star Adventurer and 450D go wide on Orion with 2 min subs.

The stacking of the total of 5hrs worth of images (300 actual images in all, not counting the calibration frames) took 18hrs in Astro Pixel Processor. The problem with shooting with a DSLR I’ve found is that the file sizes are much larger than the ASI178MC that I usually use for deep space astrophotography. Unfortunately the field of view is too small with that camera, hence resorting to the DSLR, the stock 60D.

Am I happy with what I have so far? Absolutely! The image is looking pretty clean and crisp and to my eye there’s some amazing nebulosity there. One thing I’ve noticed with a lot of images of this region is that most tend to go overboard with the blue in my opinion. Which is great, but there are so many orange stars in there that it’s a shame to lose those in amongst all of that. I try and work hard on the star colour calibration for this very reason and I think I have it. In addition, the extra 3 hours I managed on the last run has opened up the field of view as well so it’s not so tight in the frame, and now has some room to “breathe.”

Could I have obtained more of the background with longer exposures? I think absolutely yes, but it wasn’t about that. It was about trying to obtain the cleanest image of this cluster that I could and I feel I’ve achieved this. Maybe next season I’ll add more time and go for the outer regions more.

5 hours in total with the stock 60D using 1 minute guided subs at ISO 800 with the 72ED

I think for this one I’m going to call the project complete for this year. We’re heading into a full moon period now and I’m not expecting it to become any easier to image as we head out of it. There’s plenty of space up there to keep me busy and I’ve already started or continued with other projects (keep an eye open for these in coming weeks.)

Thank you for taking the time to follow me as I’ve gone against the weather, the equipment and lack of general imaging time to produce what I think is my best image so far of this jewel of our sky at night. Until next time, clear skies all!

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