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Advice on stacking different exposure times please.


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I’m still very new at this and so far I’ve only stacked subs taken with the same exposure.

If I try to stack subs with different exposures but at the same gain and temperature do I put them all into DSS or similar and stack together or do I process them separately?

That then leads on to the question of what do I do about calibration frames?

Any advice will be greatly appreciated.

 

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Following with interest.

Yesterday I had the opportunity (first night in weeks) to play with my astro-stuff (in the presence of a bright moon) and took 3 hours of the Pacman Nebula split in 12x300s, 15x240s and 20x180s, all at ISO800. I wanted to use APT histogram to set the optimal exposure time, but all three tests seemed overexposed (further to the right than expected). Next cloudy night (tomorrow unfortunately) I'll have a go with the data integrating all subs in a single image. Maybe not very practical in this target, but a new technique to learn.

Regarding calibration frames, since I only use Flats and Bias (both ISO-dependent only) I will use a single set for all the subs.

If you use Darks, I believe you will need a set for every different exposure time.

Looking forward to hear from the experts.

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Matching darks are necessary, if you plan on using darks at all so a set of darks for every different exposure time. Bias, flats and darkflats are ISO/gain/temperature dependent so you can use them with all the different exposure times.

In Deepskystacker you can use the "groups" function at the bottom to separate the different exposures into their own groups. Drop set1 of frames to group 0, set 2 to group1 etc. This is also used for projects spanning several nights, each night in its own group. DSS stacks all of them together in the final image.

Different stacking combination methods for the lights can also have an effect. You can try using the entropy weighted method if the exposure times were very different, like 2s x300 + 120s x 100. But generally stack as you normally would, with median kappa-sigma.

In Siril with using Sirilic you can also create a project with multiple sessions and drop the different sets into those.

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1 hour ago, ONIKKINEN said:

Matching darks are necessary, if you plan on using darks at all so a set of darks for every different exposure time. Bias, flats and darkflats are ISO/gain/temperature dependent so you can use them with all the different exposure times.

In Deepskystacker you can use the "groups" function at the bottom to separate the different exposures into their own groups. Drop set1 of frames to group 0, set 2 to group1 etc. This is also used for projects spanning several nights, each night in its own group. DSS stacks all of them together in the final image.

Different stacking combination methods for the lights can also have an effect. You can try using the entropy weighted method if the exposure times were very different, like 2s x300 + 120s x 100. But generally stack as you normally would, with median kappa-sigma.

In Siril with using Sirilic you can also create a project with multiple sessions and drop the different sets into those.

Thanks a lot for that, it’s something that’s puzzled me for a while and I couldn’t find any information on YouTube.

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