Starting out with Deep Sky Stacker

[StuartT]

I am dipping my toe into the water of image stacking. Last night I took a relatively small number of images (20) of a star field with a bright star in the centre. I have not taken any flats or whatever, I just wanted to try DSS in a very basic way to see if I could align the images and stack them.

The 20 images were shot at the prime focus of an SCT with a Canon EOS750D (10sec exposure at ISO800). An example is the first image below. The tracking is slightly off, so the stars drift slowly in position through the set. But I am assuming the registration process takes care of that. 

Problem is, the first go at stacking makes them into trails (so doesn't seem to be registering them properly (second pic below). I set the threshold quite low and it was detecting plenty of stars (about 300)

Can anyone help me with the basic settings I should be using? I was basically following this article by way of a tutorial.

[AstroExploring]

What setting do you have selected in the Results and Alignment tabs in the Stacking Parameters window? I made a video tutorial for DSS about 12 months ago which you hopefully find useful https://www.astroexploring.com/deepskystacker you might be able to skip to about the 7 minute mark to confirm your settings for stacking. 
 

HTH

[StuartT]

2 hours ago, AstroExploring said:

What setting do you have selected in the Results and Alignment tabs in the Stacking Parameters window? I made a video tutorial for DSS about 12 months ago which you hopefully find useful https://www.astroexploring.com/deepskystacker you might be able to skip to about the 7 minute mark to confirm your settings for stacking. 
 

HTH

Results tab : Standard and Alignment tab : automatic

Thanks. I'll check out your tutorial 🙂

Edited March 30, 2021 by StuartT

[The Lazy Astronomer]

What does a stretched single sub look like? Can you visually see a very large number of stars? Maybe DSS is mistaking hot pixels or some other kind of noise for stars and that's messing with the registration and alignment.

After registration, you can click the edit stars icon (I think it's on the lower right hand side of the image on screen) and check what it has identified as a star within the frame.

It only needs a minimum of 8 stars shared between all subs to align and stack, so maybe as a quick test, re-register the images with a higher detection threshold and see what it spits out (possibly try for around 20 - 50 stars, depending on how significant the drift is across the whole set).

[StuartT]

 

7 minutes ago, The Lazy Astronomer said:

What does a stretched single sub look like? Can you visually see a very large number of stars? Maybe DSS is mistaking hot pixels or some other kind of noise for stars and that's messing with the registration and alignment.

When you say 'stretched' do you mean using the levels control in Photoshop to move the midtones point? If so, here's how one of them looks

 

[The Lazy Astronomer]

20 minutes ago, StuartT said:

 

When you say 'stretched' do you mean using the levels control in Photoshop to move the midtones point? If so, here's how one of them looks

 

Yes, that is what I meant - judging from this, I would be surprised if there were 300 actual stars in the frame, so I'm sticking with my previous theory.

Edit: removed irrelevant statement

Edited March 30, 2021 by The Lazy Astronomer

[michael8554]

13 hours ago, StuartT said:

The tracking is slightly off, so the stars drift slowly in position through the set. But I am assuming the registration process takes care of that. 

Sorry to say Stuart, DSS will reject stars that aren't fairly round, stacking won't make them round

 If you look at the stretched sub, there are only about 40 stars, so "300 stars" will probably comprise hot pixels, not stars.

If you open DSS there's their own comprehensive user guide (bottom of the side window), did you read that first ?

Michael

[StuartT]

10 hours ago, michael8554 said:

Sorry to say Stuart, DSS will reject stars that aren't fairly round, stacking won't make them round

 If you look at the stretched sub, there are only about 40 stars, so "300 stars" will probably comprise hot pixels, not stars.

If you open DSS there's their own comprehensive user guide (bottom of the side window), did you read that first ?

Michael

ok, so I have the threshold for star detection set too low. Thanks.

I didn't read the user guide 😬 but I shall now!

So I tried again with a higher detection threshold (in case it was just finding hot pixels). But still it can't seem to align them.

 

Edited March 31, 2021 by StuartT

[Adam1234]

How many stars does it detect?

[Seelive]

That last image looks like you have selected the 'No alignment' option. Can you upload a few lights to a file sharing site? I'm sure there are plenty of people who will be able to analyse the cause and/or suggest a fix to your problem. Have you tried the DSS forum?

[StuartT]

Ok thanks everyone. I seem to have it working ok now. I got an aligned image at least 😊 This is Regulus

I think my biggest problem is that my tracking won't allow me exposures longer than 10 sec, so I am prob not catching enough photons

 

 

Edited April 1, 2021 by StuartT

[AstroExploring]

What setting did you change out of interest? Glad you got it working 

[StuartT]

10 hours ago, AstroExploring said:

What setting did you change out of interest? Glad you got it working 

I was using JPG images, so I re-shot some RAW images last night and it worked a lot better

Maybe JPGs are too noisy?

[AstroExploring]

Yeah that makes sense. The compression of a JPEG probably adds too much noise, which DSS picks up as a star because the background will be very grainy. Then trying to align on the noise will be an impossible task!