Deep Sky Stacker not aligning?

[Laurieast]

Hi All,

I took 10x unguided 20 second lights at 800iso at f4 on a Canon EOS 500D with the lens at 18mm and images stored at Large JPEG so 4752x3168.

Got a good set if images pointed in the direction of Hercules, but when I stack them in DSS the final resulting TIFF looks like one long exposure with star trails.

I have tried cropping twice, tried various settings in DSS like changing the star count, but can't seem to get a normal stacked image, also tried stacking TIFF's after saving as in CS. Watched several Youtube tutorials and it looks so easy, looked here for a similar problem and can't find it answered.

Feeling like the last moments of HAL 9000 now ...

Any help please?

 

Edited September 27, 2020 by Laurieast

[Chefgage]

The first point to make is you should be shooting raw images to stack. 

[PeterCPC]

As above. How many subs did DSS say it had stacked?

Peter

[Laurieast]

Thanks Chefgage, will do next time, I had thought I had Raw + JPEG set..

PeterCPC,  It's registering 10, stacking 8, they all look ok to me. Same result just now. 

Edited September 27, 2020 by Laurieast

[happy-kat]

Can we see the registration results please, that shows star count column and score

[Laurieast]

[Paul2019]

Just going to throw it out there, recently I had this issue with my stacks when using no tracking. Turns out the issue was me moving the camera in between subs, I took 3 sets of 30 subs and moved the camera in between each set. If I stacked all the sets, or 2 of 3 the stars weren't correctly aligned but if I stacked only one set then it was fine. Maybe its something similar?

[Laurieast]

10 minutes ago, Paul2019 said:

Just going to throw it out there, recently I had this issue with my stacks when using no tracking. Turns out the issue was me moving the camera in between subs, I took 3 sets of 30 subs and moved the camera in between each set. If I stacked all the sets, or 2 of 3 the stars weren't correctly aligned but if I stacked only one set then it was fine. Maybe its something similar?

Thanks Paul,

It was very windy, but other than that it was on a tripod, and I never touched it guv. 😉  , apart from pressing the button....hmmm, but I had it on delay/countdown.

I took another set at 1600iso, but that gives the same result.

 

Edited September 27, 2020 by Laurieast

[Seelive]

With such a short a focal length lens, the image scale distortion can be quite large so any misalignment between images can cause stacking issues. 

[Laurieast]

25 minutes ago, Seelive said:

With such a short a focal length lens, the image scale distortion can be quite large so any misalignment between images can cause stacking issues. 

Zoomed in on the stacked trails.

[Paul2019]

58 minutes ago, Laurieast said:

Zoomed in on the stacked trails.

This is noise, easily removed with Darks

 

[happy-kat]

The FWHM is a little on the high side but you have a workable star count. Although the number of frames should be more than 20 try a stack using sigma clipping.

[Laurieast]

40 minutes ago, happy-kat said:

The FWHM is a little on the high side but you have a workable star count. Although the number of frames should be more than 20 try a stack using sigma clipping.

I thought you had it then when I looked at Autosave 1, then realised I'm looking at hot pixels. Autosave is still the same.

Thanks for trying!

[happy-kat]

select each frame in turn and make sure the hot pixels have not been recognised as stars, if one has pick it so it is off and save the frame, the mini icon bar in the right

[Laurieast]

I gave up with the JPEG images, no more JPEG's ever.

It was clear last night, so took some more unguided, camera on tripod, focus and shooting in BYEOS, 36 RAW Frames of 10s subs, lens up to 35mm from 18mm, and now I have stacking going on! Not perfectly round stars, but there must be a fix for that?

Thanks to all for the guidance. 

 

Edited September 28, 2020 by Laurieast

[happy-kat]

That's great. Kappa sigma clipping on the lights will help with roundness.

[Crackabarrel]

Looks much better.

Try reducing your exposure time to control roundness.

The crop factor on Canon APS-C is 1.6, so your effective focal length at 35mm is 35*1.6 = 56mm

Rule of 500 give you a max exposure length of 8.9sec

However I have had better experience using the more stringent NPF rule for exposure length to retain star roundness

https://www.sahavre.fr/tutoriels/astrophoto/34-regle-npf-temps-de-pose-pour-eviter-le-file-d-etoiles