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stacking image subs of different exposure


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Last weekend I decided to add some more data to my ha rosette.

Previously I had taken 10x 15 minute subs but because it was quite breezy this time I did 15x 10 minute subs.

Stacking all the subs from both sessions in DSS I tried all the options but each time I ended with less data than either individual 150minute session.

I tried normalizing the subs in Nebulosity2 and then stacking but with the same result.

Does this mean that I must keep to only stacking subs of equal time length.

Any advice greatfully received.

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In DSS you load all your "type 1" subs, including darks and flats etc if you have them. You will see a tab at the bottom of the screen called "main group" and next to it will have appeared a tab called "group 1". Click on the tab Group 1 and load all your "type 2" lights, darks and flats etc. DSS will then stack each set seperately and will combine the two sets into one final image for you automatically.

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In DSS you load all your "type 1" subs, including darks and flats etc if you have them. You will see a tab at the bottom of the screen called "main group" and next to it will have appeared a tab called "group 1". Click on the tab Group 1 and load all your "type 2" lights, darks and flats etc. DSS will then stack each set seperately and will combine the two sets into one final image for you automatically.

If you have got bias subs, you can put them in the 'main' tab and they will be applied to all the other groups, rather than adding them to each group individually.

HTH

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  • 2 years later...
  • 2 weeks later...

Presumably putting all the subs into DSS as indicated here, means there would no longer be a requirement to obtain individual stacks for each exposure level and then combining them in something like Photoshop? I am thinking something like the Orion Nebula which has a great variation in brightness across the image that required a number of different exposure to get the whole picture.

Presumably the end result of stacking all in DSS would be equal to combining them in Photoshop?

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Funny you're talking about Orion Nebula as recently I stacked 3 different exposure types (7x ISO3200/15sec, 6x ISO2000/15sec, 5x ISO 800/15sec) into one and the core of M42 got blown out anyway (as one would expect). So I ended up doing 3 separate stacks for 3 different layers in Photoshop, but not only align in Photoshop but layer mask too.

1) All 18x in one stack (no flats)

2) 3x stacks with flats & with Photoshop layer masking

post-39208-0-37805100-1422234878_thumb.j

post-39208-0-02763200-1422234896_thumb.j

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  • 3 weeks later...

I did a rerun of different exposures of Orion Neb using DSS. Putttng the different exposures into separate DSS tabs. The end result was an Orion Neb image without the core blown out, despite one set of exposures in one of the tabs being blown out. This suggests that putting everything into DSS, will do what has to be done manually in Photoshop to combine different exposure lengths.

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I tend to use on of the shorter subs for the reference frame for all the separate "exposure"  stacks...

The reference frame doesn't have to be checked in DSS so it's not included in the stack... 

If you use standard mode for the stacking and you will have separate files all the same dimensions that you can open and paste as layer into photoshop...

Peter...

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I might be inclined to make two separate stacked images, one from each set, give them each a similar stretch/cutback, get the background sky value the same in each then paste one onto the other in PS. Then I'd play with the opacity slider to find out at which point the blend had the best S/N ratio. Choose that, flatten and continue to stretch.

Olly

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I might be inclined to make two separate stacked images, one from each set, give them each a similar stretch/cutback, get the background sky value the same in each then paste one onto the other in PS. Then I'd play with the opacity slider to find out at which point the blend had the best S/N ratio. Choose that, flatten and continue to stretch.

Olly

That's the "reminder" I needed for what I was doing wrong...

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  • 1 year later...
On 27-2-2012 at 20:43, Bizibilder said:

n DSS you load all your "type 1" subs, including darks and flats etc if you have them. You will see a tab at the bottom of the screen called "main group" and next to it will have appeared a tab called "group 1". Click on the tab Group 1 and load all your "type 2" lights, darks and flats etc. DSS will then stack each set seperately and will combine the two sets into one final image for you automatically.

Thanks for this! I was wondering how to do this as a beginner in astrography. 

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  • 1 year later...

I used to get a better result by stacking the two different lots of images into two stacks and then stacking the stacks.  Pretty much what Olly has said, except DSS will align them for you as the chances are the orientation and framing it going to be a little different for each night.

Carole 

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  • 2 months later...
On 28/02/2012 at 08:19, Demonperformer said:

If you have got bias subs, you can put them in the 'main' tab and they will be applied to all the other groups, rather than adding them to each group individually.

HTH

Is this also true for flats? Can you just add them to the main group as they do not match the exposure time anyway? Happy to hear. Thanks all. 

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On 24/08/2018 at 11:46, widotje said:

Is this also true for flats? Can you just add them to the main group as they do not match the exposure time anyway? Happy to hear. Thanks all. 

If the flats match both groups, then yes add them to the main group and they will, like the bias, be used for all sets.......... all calibration frames added to the main group will be used by ALL groups, unless a set is added to a specific group, it will then only act on that group. 

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  • 1 month later...
On 31/08/2018 at 15:13, martin_h said:

If the flats match both groups, then yes add them to the main group and they will, like the bias, be used for all sets.......... all calibration frames added to the main group will be used by ALL groups, unless a set is added to a specific group, it will then only act on that group. 

So does that mean you shouldn't use darks in the main group? Bias and flats should be fine, but darks should mirror the exposure of the lights. It's fair enough only putting group 1's darks in group 1, but any darks in the main group would also be applied to group 1?

If that's the case, is it best to put only bias and flats in the main group, and then each set of matched lights/darks into the numbered groups?

 

 

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