First M51 In Awful Conditions

[The-MathMog]

Went out Tuesday night to do some more practice with my new Celestron AVX mount, as a clear night was predicted. I wanted to improve my polar alignment and tested drift alignment for the first time. It came out very well, and I thought that I'd better not let it go to waste, so I went on to capture M51.

The thing is though, I had neglected/underestimated how much wind there would be that night, and it got horrible very quick. The medium wind (according to weather stations) was around 10m/s with gusts being more than that at its peak, but stubborn as I was I just endured it, knowingly that the a lot of the subs would be straight for the trashcan.
On top of that, it was 1.5-2 days after the full moon, so the sky was veeery lit up, proving even more of a challenge. But again, the lack of clear skies lately, made me not want to waste it.

So I ended up gathering around 64 frames of 1 minute at ISO 6400. I did try doing 2 minute and 3 minute exposures. They didn't show much trailing, but were a lot more prone to the strong gusts that made the stars jiggle, so I kept to doing 1 minute subs. And even out of those, only around 4 subs were decent without much traces of the strong wind..

Of course deep sky stacker didn't like my horrendous shaped stars, so I went on to stack 60 of them manually (at this point I didn't care about the shapes of the stars, I just wanted to see what data was hidden in it), stacking 5 at a time, and then stacking those 12 stacks 4 at a time, and then the last 3, for an estimated total exposure time of 60 minutes +- (as I was using a remote without a timer)..

Nonetheless, this is what one of the better subs looked like, and what eventually came out of it, and I am glad that I could at least pull something out of this, and this just makes me want to get out and shoot even more (preferably on less windy nights)!

60 Subs (1min+-)
60 Min Total Exp
ISO 6400
20 Dark Frames
Celestron 130 SLT OTA
Celestron AVX Mount
Baader 2.25 Barlow (For focus)

 

-Mathias

[mikey2000]

I was immediately drawn to the subject title - M51 is high on my list of things-to-photograph!

 

Your story is one of Intense Labour!  Well done for persisting!   From the initial sub example, I can't help wondering what software you used to stretch the image afterwards -  I imagine you may have a little more detail hiding in there somewhere :-)  I also spot a bit of coma in those stars. DSS was a lot happier with my shots since I got a corrector.

 

I have a funny feeling you might be just a month or so behind me in stumbling into autoguiding!

[The-MathMog]

24 minutes ago, mikey2000 said:

I was immediately drawn to the subject title - M51 is high on my list of things-to-photograph!

 

Your story is one of Intense Labour!  Well done for persisting!   From the initial sub example, I can't help wondering what software you used to stretch the image afterwards -  I imagine you may have a little more detail hiding in there somewhere :-)  I also spot a bit of coma in those stars. DSS was a lot happier with my shots since I got a corrector.

 

I have a funny feeling you might be just a month or so behind me in stumbling into autoguiding!

Haha indeed it was a intense!

It was all done in Photoshop CS2. Stacking, subtracting darks and stretching. And you might be right. But that sub example was also one of the better subs, most of the subs had worse data or worse stars too because of the wind, which is also apparent in the final image as I just used all the frames, making them all "stretch and blur" in one direction. Processing the images is still very new to me, so a bit of a learning curve, and as of right now, I try to not overdo it whenever I do it.

A coma corrector and auto-guiding is indeed my next step in astrophotography, so your estimation isn't all that wrong, as I will probably get those in a month or two. The bank was just broke with the AVX mount last month, so it needs to recover a bit hehe. Whenever I try to do longer subs than 1 minute I will often see what looks like periodic errors, at least not a consistent star trail, so guiding is something I'll be looking forward to, as well as doing Periodic error correction.

The coma might also be enhanced by the use of the barlow, or is that a wrong idea? And was it in the initial photo that you see the coma?

[mikey2000]

The coma isn't really that bad.  I have a 150mm reflector and shoot with an APS-C camera - stars are definitely 'fan shaped' at the edges, even half way from the centre on my set up.  So for me the coma corrector is essential unless I only look at the centre of the image.  (is your pic a crop or the full readout?)

 

I'm no expert on mounts, (I'm a newcomer too!) so I had to google your AVX.  I think it looks like a bit like an upgrade on my EQ3 so I'm nearly 100% certain you will benefit from a autoguide setup.

 

As for processing, I have a newer version of photoshop and never really managed good results on DSS stacked files.  Having seen the first sub, I can't see why DSS wouldn't like it - I've managed to stack much worse than that!  Once you get the DSS output, I'd highly recommened taking a look at startools - free to try and cheap to buy (25$AUS if I recall).  The free trial doesn't let you save but you can still take screen grabs....  Why spend all that money on a scope and mount then find you can't process the image properly!! ;-)

 

If you like, you can put the subs somewhere like dropbox and I'll have a go at stacking them too.

[The-MathMog]

1 hour ago, mikey2000 said:

The coma isn't really that bad.  I have...

Alright then. I did have quite a lot worse coma when I put the barlow closer to the camera. That was quite horrendous. And yeah this is actually a full frame, at least the first image. Right now I am stuck at using the barlow lens, for focus reasons, at least until I can find a place that sells the right screws for me to move the primary mirror up the tube.

From what I've heard and read, is should be about the equivalent of the HEQ5 mount, with maybe a slightly lower payload. Definitely I will! At this point I've been able to get some 3 minute unguided subs, but the periodic errors make me throw out at least 3/4 of them.

I absolutely agree. And processing is something that I am looking quite a bit into at the moment, using the tools I have available (I don't wanna spend more money than I have to at the moment :p)

I actually don't have the original RAW files anymore, as I had to convert them into a usable file  (Photoshop wouldn't handle the NEF file from Nikon), so I only have PPM files, which is around 4 GB of data. I don't have that much space left on my dropbox unfortunately haha! But if you wanna have a go at the final stacked image, be my guest!

https://www.dropbox.com/s/op2q56k1mvvwsly/Last Stack 60 Images.tif?dl=0