Help needed with registering!!! - Forums

Topic starter

Apr 21, 2026

Hey everyone,

I’m trying to stack data on NGC 4216, but I keep running into registration issues.

My FOV is pretty small (~0.5° × 0.3°), and I’m shooting 10s subs with an ASI662MC on an alt-az Celestron SLT130 (~300 frames total). There are very few stars in each frame, and both Siril and SASPro are struggling — lots of frames don’t register, and SASPro mismatches stars.

I’ve already tried lowering thresholds, affine transforms, mono/green channel, etc., but still not great results.

Is there any way to register data like this when there are very few stars in the FOV?

(Feels like I’m hitting the limits of short exposures + small FOV + alt-az 😅)

Any advice would be really appreciated.

Well written Respectful Engaging

Tony Gondola

Frequent contributor

Exemplary contributor

Apr 22, 2026

One trick with Siril is to take a sub frame and run dynamic PSF on it. Image Processing>Star Processing>Gear Icon.

Tell it to detect stars and keep reducing the threshold. Keep doing that until you see a sudden drop in FWHM that indicates you are just detecting noise, remove those if present. You want to detect at least 8 stars, 20+ is better.

Now, run your regular stacking script. It will run perfectly if you detected enough stars. If it still has registration issues:

Change your working directory to the process directory

Go to the “Sequence” tab

Search the sequences and select the pp_light_.seq sequence

Click on the stack of images icon in the lower right corner of your screen and make sure all images are checked

Click on the “Registration” Tab

Registration method should be “Global”

Reduce “Minimum Star Pairs” to 4

Click “Go Register” At this point all the subs should register properly. Once that’s done, click on the “Stacking” tab and stack.

If you can’t find at least 8 stars then repeat the above but instead of using the “Global” registration method, use the 1-2-3 star method. It’s all a huge pain in the ass but it can be made to work.

Good luck!

Well written Helpful Engaging Supportive

Interactive Sky

Topic starter

Apr 23, 2026

Tony Gondola · Apr 22, 2026, 02:33 AM
One trick with Siril is to take a sub frame and run dynamic PSF on it. Image Processing>Star Processing>Gear Icon.
Tell it to detect stars and keep reducing the threshold. Keep doing that until you see a sudden drop in FWHM that indicates you are just detecting noise, remove those if present. You want to detect at least 8 stars, 20+ is better.
Now, run your regular stacking script. It will run perfectly if you detected enough stars. If it still has registration issues:
Change your working directory to the process directory
Go to the “Sequence” tab
Search the sequences and select the pp_light_.seq sequence
Click on the stack of images icon in the lower right corner of your screen and make sure all images are checked
Click on the “Registration” Tab
Registration method should be “Global”
Reduce “Minimum Star Pairs” to 4
Click “Go Register” At this point all the subs should register properly. Once that’s done, click on the “Stacking” tab and stack.
If you can’t find at least 8 stars then repeat the above but instead of using the “Global” registration method, use the 1-2-3 star method. It’s all a huge pain in the ass but it can be made to work.
Good luck!

Thank you very much, Tony,

I followed the steps, and it worked perfectly.

Thank you. Clear Skies!

Well written Respectful Supportive

Tony Gondola

Frequent contributor

Exemplary contributor

Apr 23, 2026

Great!