M16 from Blacklands 18-8-12

[Carole]

I was pleased for the opportunity to image this subject which is behind the trees at home and also at Rother Valley. Apart from 2 x 5min subs at High Halden last year (before it clouded up), this is my first attempt at this object.  

20 x 5mins 800 ISO, Modified Canon 450D @ 18 degrees and very damp
Skywatcher ED120, guided with PHD and dithering in APT on NEQ6
I stupidly left the CLS filter in place

There is a strange problem with the stars in this which seems also to be a problem in my M16 at High Halden.  Guiding graph was fine (Mike saw this at the time), I am just wondering what the cause is likely to be.  Fortunately it doesn't show up unless you look at the very large version.

Larger file:
http://gallery.orpington-astronomy.org.uk/albums/userpics/10047/M16_Blacklands_18-8-12_ED120_20_x_5mins_800_ISO_full_frame_CLs_filter_dith_APT.png

[Carole]

CROP of the central area.  

[MarkS]

It looks good - especially the central crop -you've got some good detail there and the colouring looks right. The noise is probably caused by the high temperature that night. 

The CLS filter has probably helped here by keeping doen the background glow and therefore making it easier to precess.

What problem with the stars are you referring to?

Mark

[Carole]

Thanks Mark.

What problem with the stars are you referring to?

Well it seems to be worse on the original subs, stacking and processing seem to have improved it somewhat.
Basically, egg shaped stars with some chromatic aberration.  

This is a crop of an enlargement of one of the RAW subs.



Carole

[Fay]

you did well with  the DSLR in those conditions Carole, especially with all the other lights as well. were those stars at the edge? I get stars like that at the edges , but that is when I am using the wide angle lens's

[Carole]

were those stars at the edge?

No Fay, they were all over.  I showed Mike while I was imaging, and also my guiding graph.  He wondered whether the DSLR was in crooked, but I don't think it was.

Carole

[RobertM]

Nice image Carol.  I did have to look quite closely to see the egg shaped stars.  Since it's so slight there could be that type of issue if there was a tiny bit of drag on the guide camera.

[Carole]

Thanks Robert.  I do normally tie up the guide cable leads so there is no chance of snagging, or waving around, so maybe I tied them up too tight on this occasion.  I will be more careful next time.  It would be great if that was all it was, as it's easily rectified.

Carole

[RobertM]

Ah, now I think we would all be happy if things were that easy   

[JohnP]

Well done Carole - Another to tick off the list. Your result is very good & like Mark points out for an uncooled DSLR in mid summer its superb..

John

[Carole]

Thank you John.

Carole

[Carole]

Following a tip on another forum I have re-processed this, and also found a tip to adjust the slightly egg shaped stars.

This shows less background nebulosity, but I think the detail is better.



Carole

[Rocket Pooch]

Oh dear thats not very good is it.

[Carole]

Is it not?
Had lots of good feedback on other forums.

please explain.

Carole

[Rocket Pooch]

I'm refering to the odd shapped stars, the image itself is ok for a DLSR.

[Carole]

odd shapped stars

Oh yes, I don't know why that was, as stated in earlier post, the guide graph was OK.  Normally I don't have a problem, could it be my polar alignment was a bit out?

I managed to process out the slightly oval stars in the re-process.

Carole