Deep Sky Stacker queries...

[AndyUK]

I'm still trying to get to grips with DSS and thought I was making reasonable headway (and getting fair results considering the length of sub exposures I've been using), but I have 2 queries (at the moment!):

1. Embedded or Applied changes? I'd been using applied to date, but I found a resource on the web that advised one should ALWAYS embed them so that better colours can be brought out in Photoshop... Is this right?

2. Stacking Images from > 1 session. I've seen posts that mention they've taken a total of 12+ hours of images, so presumably they've been shot over multiple sessions and then stacked all together... and of course then there images that have been combined with different exposures (or maybe that's a totally separate subject - Please excuse my naivety!)

I know how to perform (or at least theory of) a single session stack (with associated darks, flats, flat dark etc), but (and I have a feeling that this may be a silly question), how do you apply a 2nd and 3rd nights session etc whilst associating the "correct" darks, flats, flat darks etc from the appropriate session...?

[jgs001]

Good questions Andy...

1) The developer of DSS recommends embedding the adjustments only as the adjustments in DSS are not designed for completing the image. However, in reality, go with what works for you.

2) Within DSS, if you add any file to the list, look along the bottom and you will see a new group, called group 1 appear. Then, clear out the item in the master group. Add your first nights data into group 1, include the calibration frames. Then add the second nights worth of data into group 2 (which is added when you put the first file into group 1) and repeat as needed for each nights data into more groups.

You can use the Master group for any files that are to be used across all nights sessions, so for instance your bias frames could be done that way.

[AndyUK]

Cheers John - So the first one's a suck it and see... I'll try a restack / "embed" on one I previously produced with "applied" and then reprocess to see what difference I get. Again, with the limited exposure length subs I've been taking to date (30s) my SNR has been pretty poor, so I really need to start again.

Regarding multi-session stacking, I've never noticed the little "main group" tab at the bottom... until just now. I haven't got any multi-session images worth "group" stacking yet, but it's very useful to know where it is - Cheers!

[jgs001]

Np Andy... the first, yeah pretty much... I started out using the adjustments from DSS as I found it so much easier to do, but have moved on and now embed only as I find I can achieve better results without it. I think it's one of those things that can help if you're not comfortable with the processing steps.

I've used 4 groups as my largest, but DSS seems to do a very good job at sorting it all out for you. I'm now in the habit of creating group 1 and then putting all my image data for the first night in that, just in case I go back to have another session on the same target.

Sorry I missed one... as for different exposures, in theory, the entropy weighted is designed for that, although I'd use groups to seperate the sets and darks, or you can run multiple stacks of each set of exposures and combine afterwards.

[AndyUK]

Cheers again John - Being totally honest, it's the post stacking processing I'm now feeling most "lost" with, but I think I'd rather (try and) do any image processing in photoshop than in DSS so I'll use embed from now on.

I've tried to follow some step-by-step image processing I've found on the web, but some of it just blows me away - I can see that it DOES work... but why that number of pixels / thresholds / layers? Why invert, gaussian blur and reinvert... and why with those settings etc...! . I guess I just have to be patient and use a bit of trial and error... but that's a different minefield, er, subject entirely.

Now that you've introduced me to that tab, I'll be following your process and leave the main tab blank so that it's always possible to add another session later - That's an excellent (non-documented) tip...!

With regards to different exposure stacking / blending, I think I'll leave that alone for now... I need to get some good quality subs first - longer exposures (guided hopefully) and less light pollution is my first goal and then we'll see which wall I hit next. Thanks again...!