M13 Globular Cluster on Sunday Night (3rd-4th)

[The Thing]

21 lights processed in DSS. 1h 10mins mixed 4minute and 2 minutes subs.
LX90 8" f5.5(probably) with Baader Telecompressor. Minolta Dynax 7D & DSLR Shutter. SKywatcher AT80 with modified SPC900NC and wxAstrocapture for guiding.

This is a full size crop. I'm happy apart from what look like trailing hot pixels. Any ideas/advice?.

[RobertM]

Hi Dunc,

That's looking very good.  You have quite a few hot pixels but as they seem to have drifted during your capture you should be able to get rid of most of them using a Sigma stacking algorithm like SD Mask or Sigma Clip.  If you use DSS than I'm sure one of the stacking options looks like *Sigma*.  Other than that the stars are a good shape and the apparent drift should work in your favour once stacked.  There also looks like a bit of rotation - could your polar alignment be a bit off ?

Hope that helps
Robert

[MarkS]

Duncan,

Nice one!  You've got some good data in there - you just need to make the most of it.

Shoot some dark frames (at the same ambient temperature as your imaging), average them and subtract them from your lights - that will get rid of most of the background noise.  Use sigma stacking as well to clean it up further.  But as Robert says, sigma stacking alone will also make a big difference.

Boost the colour saturation (by a serious amount!) and you'll begin to differentiate the star colours (reds and blues) in the cluster.  I would also perform a 2x2 binning of the data.

Don't worry about the drift - you've got it just about perfect - not too much and not too little.  Drift is your friend - without drift you have to resort to highly technical approaches like "dithering" to iron out patterns in the CCD noise.

Mark

[RobertM]

Forgot to say.  You might also consider a wee bit of sharpening to tease out some more core detail.

[The Thing]

Great comments! Thanks.

I would like to sort out the hot pixel streaks. This is processed with a straight average as Sigma stacking produced a blob of red (Swine flu in DSS?). Maybe it was some other setting. I have read the manual properly now so should be able to do better. There is no sharpening applied or any other post processing apart from what you can do in DSS.

I used darks but they are not matched to the 2 minute subs (from a previous session) only the 4 mins. I will look to see if I have some two minute darks (the temp won't be right but hey ho) then I can use the Groups feature in DSS. The flats are OK as the DSLR wasn't moved between sessions.

I have made a mount for my Meade finder scope so I can use it for polar alignment - a compass is far to iffy. Now I just need an occasion to use it.

[The Thing]

Reprocessed in DSS using a custom area and file groups for the two different imaging sessions ligths and darks with common bias and flats in the Main group. Kappa Sigma clipping was used as suggested. Kappa 0.9 & 3 iterations, cosmetic hot and cold pixel removal and some tweaking in the Processing area.

The 0.9 Kappa rejected all the brightest pixels in the saturated stars in the 240s exposures leaving the dimmer pixels from the 120s exposures thus giving better colours. Saturation was also set at +29%. You can just make out NGC6207 top right.

[Fay]

Looks like you are all ready for next week, Duncan, with your results!  That is if I have not ruined ther weather!!

[The Thing]

Thanks Fay.

If the weathers bad there's always the pub. We'll just have to designate any OAS affiliated camper vans present as pubs and pile in.

[RobertM]

The background is much better and you've got more faint stars showing though I think perhaps the stars are a little over colour saturated.  Star colouring is always something I find very difficult so I'm probably not best placed to comment let alone criticise. 

[The Thing]

Thanks Robert,
I always overdo colour if there is any. I might go for more subs at DSC, I think I can get better focus and possibly re-collimation will help (needed after the trip down to Biddenden).

[The Thing]

Taken at Woodlands Park camp site in amongst the caravans.

20 subs, 12 at 120s 8 at 240s. Knoica Minolta Dynax 7D DSLR, Meade LX90 8", Baader Alan Gee II Telecompressor at shortest setting, no Orion Skyglow filter.



Processing is nearly there.

[Fay]

Hey Duncan, that is really coming along nice!!!!!

[Rocket Pooch]

This is looking very good