Image integration question

[Gavin1234]

Just a question about integration in PixInsight. I’ve been told many times that taking some long exposure subs plus some shorter ones will help my image so I’ve done exactly that.

As an example I have a whole bunch of subs of helix ranging from 15 minutes right down to 10 secs. To keep this example simple let’s say I have
50 x 30 sec lights
50 x 30 sec darks
10 x 5 min lights
10 x 5 min darks
50 x flats
250 x bias

So first question is that I’ve been assuming when people tell me to take long and short exposures they mean that I should stack them all together. Is that correct or do I make a separate images and then copy one onto the other as a layer?

Next question, do I mix them all together I.e just ignore the fact that they’re two different length exposures or do I make 1 x 5 min master dark and 1 x 30 sec master dark etc and then just stack the final two calibrated, aligned, debayered, registered images together?

Any links to tutorials on this would be greatly appreciated. I haven’t been able to find one yet. I would prefer to do it manually instead of batch pre processing if at all possible.

Thanks in advance

[RickS (Rick)]

No, don't try to stack them together. You need to stack each sub time separately (and calibrate with appropriate length darks) and then combine the separate masters with HDRComposition.

This is only worth doing with targets that have a high dynamic range. The Orion Nebula is a good example. The Helix is not a good example and doesn't need HDR.

Dunno about a tutorial. Warren Keller's IP4AP or Adam Block's adamblockstudios.com might be worth checking out.

Cheers,
Rick.

[Gavin1234]

Thanks very much Rick. I’ve found a tutorial on HDR Composition. If anyone else is interested it’s https://youtu.be/yB0_g58CQBY

So with lower dynamic range targets you’re saying don’t bother with different length exposures? Or combine them through some other method.

[RickS (Rick)]

Originally Posted by Gavin1234

So with lower dynamic range targets you’re saying don’t bother with different length exposures? Or combine them through some other method.

There's generally no need to take different length exposures for "easy" targets, IMO at least...

Cheers,
Rick.

[Gavin1234]

Ok thanks again Rick

[sil (Steve)]

Originally Posted by RickS

There's generally no need to take different length exposures for "easy" targets, IMO at least...

Cheers,
Rick.

True, but if you have existing subs from different times with different gear and settings you can still combine them nicely. But as Rick said there is no need on most targets. Galaxy cores and some tight globular clusters too can benefit from using multiple exposures, basically if part of the target tends to become an overblown blur of white you can try multi exposures and hdr combine to try to retain detail across the whole target. Experiment though, hdr techniques are often obvious in the final image, dont overdo things.

[RyanJones]

Hi Gavin,

I've found stacking different subs handy for avoiding blow out in the centre of nebulae. I've not done different lengths but I've done different ISO. If you are stacking in DSS, upload all the first set of subs with their appropriate darks and flats etc. At the bottom of the window where the subs are listed there in a tab saying " group 1 " and so on. Put each different set of subs, darks etc into each group then stack as required. DSS takes care of the combination for you.