North America Nebula 12-6-11

[mickw]

Thought you already had that record 

[MarkS]

But how many re-processes can one thread take?

It's good to see your progress and everyone learns from it.  Getting the processing "right" is one of the most difficult aspects of astrophotography.  I put the word "right" in inverted commas because everyone has their own subjective idea of what is right.  

I don't use Photoshop myself for processing but I notice there is a new book just out called "Photoshop Astronomy" (reviewed p81 July 2011 Astronomy Now).  It may well be of some help.

My own technique tends to be very "purist".  I like to process the entire image in exactly the same way.  For instance I don't perform operations such as "select stars" because that would imply you are going to treat stars in a different way to the rest of the image.  That offends my "purist" instinct.  I'm not saying my approach is "right" and others are "wrong" - it's just the way I presently try to do things and I'm currently happy with the results it gives.  Maybe further down the line I'll find my approach too limiting and I'll adopt a completely different style of processing.

Mark

[Carole]

OK, got a lot more subs last night.  Now a total of 38 x 5mins (3hours 10 mins).
On first inspection this doesn't look too bad, but if you enlarge the image there is strange streaking accross it.  I have had this once before and have no idea what is causing it.  I stack and process the same way each time.
This one was stacked in DSS in two batches (both from scratch) and there were no streaks on the first batch.  I wonder if it's something to do with the double batching.  

Any ideas?  Have not gone too far with the processing as it seemed pointless in the circumstances.  Might have a go at processing in one batch and ignoring the different flats and darks just to see what happens.  You can get the larger image from the gallery. 

[MarkS]

Carole,

Try processing the second set of subs separately - I think you'll find the problem lies with them.  The streaks are caused by the fact that you suffered drift between subs during the acquisition and that your darks are not well matched to the data.  The streaks are then caused by the hot pixels (and warm pixels) leaving "trails" during stacking because the darks have not removed them first.

Mark

[Carole]

Hmmm, I wonder then whether it was my efforts to manually dither and perhaps overdid it 

Carole