Deep Sky stacker - scoring images

[Tommohawk]

Long story short - I did some more subs through the night for Elephants trunk. The framing is slightly different from my first set done some weeks ago, and of course there was the tail end of some lunar LP.

So how do I choose the best of the bunch from the 2 sets? Use the DSS scoring? Or maybe use the FWHM rating? would the latter give better comparison given the different conditions?

Thanks in advance.

[geordie85]

When you click register there's an option to stack the best XXX amount of subs. I usually have it set to around 80%

[Filroden]

1 hour ago, Tommohawk said:

Long story short - I did some more subs through the night for Elephants trunk. The framing is slightly different from my first set done some weeks ago, and of course there was the tail end of some lunar LP.

So how do I choose the best of the bunch from the 2 sets? Use the DSS scoring? Or maybe use the FWHM rating? would the latter give better comparison given the different conditions?

Thanks in advance.

I think the DSS scoring is how it's assessing "stackability" and takes account (amongst other factors) of the number of stars it can detect - not really (just) a measure of the quality of the image. I'd probably assess FWHM (and given I use Pixinsight now rather than DSS, I can also take account of star eccentricity and overall signal to noise ratio). Ultimately, see what FWHM and DSS scores are suggesting then visually inspect the worst ones to make sure you agree the right cut-off value.

Any % cut of subs risks including bad or excluding good subs as it's just an arbitrary bar.

[Tommohawk]

12 minutes ago, geordie85 said:

When you click register there's an option to stack the best XXX amount of subs. I usually have it set to around 80%

Thanks yes I have figured out how to choose the best from a single run of subs, either by x % or over a threshold. Never been quite sure how many to stack - I usually try and see if theres any obvious drop off somewhere in the list and stack above that.

But my point is if you have 2 lots of subs, which may have different underlying conditions eg lunar LP, or maybe a different star set due to different framing, isnt it possible that one set will score higher just because they happen to include some higher scoring region? If so, is there a better way of comparing the 2 sets?

Whilst posting this, I had DSS re-registering the 2 sets of subs, and interestingly the highest scores are mixed from both groups - maybe this answers my question is maybe DSS can be relied on to score independently

[Tommohawk]

2 minutes ago, Filroden said:

I think the DSS scoring is how it's assessing "stackability" and takes account (amongst other factors) of the number of stars it can detect - not really (just) a measure of the quality of the image. I'd probably assess FWHM (and given I use Pixinsight now rather than DSS, I can also take account of star eccentricity and overall signal to noise ratio). Ultimately, see what FWHM and DSS scores are suggesting then visually inspect the worst ones to make sure you agree the right cut-off value.

Any % cut of subs risks including bad or excluding good subs as it's just an arbitrary bar.

Thanks Ken - the DSS "score" and the FWHM do seem related, but not quite the same. Your post crossed with mine above - it may be that DSS can stack different framings independently.

Sometime, when we've had a run of superclear nights and I'm bored of clear sky and have run out of projects, I might try comparing different sets of subs having the same conditions, but framed differently to test this idea. Will this happen anytime soon?... probably not.