Reworking old data

I've been spending some time over the past few days reworking old data. For several reasons, 1) I've got nothing new to work on. 2) To see what I could do with some new tricks I've discovered. 3) To see what effect a couple of changes to the stack made with new information I've read.

Well, first off the stacking. As I've found that darks actually seem to detract from the faint stuff in my images and in fact make noise processing more difficuly, I decided to remove them from the mix. I also read that dSLR's automatically subtract a Bias frame from each image taken. I've only seen it mentioned in one place, but given that when I include bias frames in the mix, I get odd results with horrible green casts (without using a CLS filter) this correlates nicely.

So first off, I went back and redid my M81 M82 data. It took a few goes to get it right, but some tips I found, in the end set me on the right path

Here's the original for reference



The first attempt, where I've overdone the processing...



Then refining a bit more



and finally, about as good as my processing skill can get it at the moment. I'm sure that at some point, I'll be better at this, and will also grab some more data to add, and can therefore improve it further.



I know I've got some oddities in the background on this, that's caused by the odd overlaps between framings over three nights. That's something I do need to work out how to deal with it, but I'll get there in time.


I then moved onto my M51 data. This was originally processed with no darks, but including bias frames, and the green cast is pretty obvious



So, restack, and reprocess, using a similar process overall to the last M81/M82 I ended up with



This time, however, I didn't crop the image, but used the DSS Drizzle feature to enhance the image scale. It's worked, but I'm not sure there's much benefit over cropping to be honest. With cropping the stars in the background remain smaller, but with drizzle they seem to grow a little...

Here's another experiment, but this time with 3x drizzle instead of 2x, this was just to see what the effect would be, and if it was something I could use and get away with in future.



It's got potential, but I'm not 100% whether it'll be that useful.