No stacking with 120sec exposure and guiding

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
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bemo47
Posts: 29
Joined: Sat Apr 21, 2018 12:06 pm

No stacking with 120sec exposure and guiding

Post by bemo47 » Sat Jan 11, 2020 10:45 pm

Hi,
Second time i try to do long exposures, 120sec, after having activated the guiding with PHD2.
1st time my guiding was quite bad, but now the guiding is quite good, gloabl RMS error of 0.14, and the Live stacking of SC doesn't want to stack frames.
I put here the screen shot of SC showing an individual frame, but the log says that less than 3 stars have been detected, and same for all subsequent frames.
For the 1st session i thought that it was due to bad guiding, but tonight guiding is good.
So i am not sure to understand the reason for such issue....

Remind about my configuration :
- Newton 200x800 f4
- Mount EQ6RPro
- Imaging with ASI1600MC
- guiding with ASI224MC on 50x205 scope
1.JPG
1.JPG (201.9 KiB) Viewed 980 times

BlackWikkett
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Re: No stacking with 120sec exposure and guiding

Post by BlackWikkett » Sun Jan 12, 2020 5:34 pm

Hi bemo47

Check out https://docs.sharpcap.co.uk/3.2/#Live%20Stacking see the alignment tab section.

The settings I use that usually always work for me. Please note these settings are provided as a starting point and you'll need to adjust for your camera and equipment.

Noise reduction 1 or higher
minimum star width 4
maximum star width 16
black level threshold 50
digital gain 2x

When adjusting these settings I recommend you only change one setting at a time take a frame and check the amount of stars detected. Eventually you find the best settings for your combination of scope, camera and sky conditions.

-Chris

bemo47
Posts: 29
Joined: Sat Apr 21, 2018 12:06 pm

Re: No stacking with 120sec exposure and guiding

Post by bemo47 » Sun Jan 12, 2020 8:27 pm

thanks for the feedback.
when i check the parameters for alignment, i have :
- noise reduction 0.5
- minimum start width 1
- maximum start width 16
- black level threshold 50
- digital gain 8x

so i will try next time tomake changes....

what is strange is that for 30sec exp i don't have any issue, it happens when i increase the exposure.

But i will try that,

Thanks again,
Bernard

BlackWikkett
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Re: No stacking with 120sec exposure and guiding

Post by BlackWikkett » Mon Jan 13, 2020 12:57 am

If you're getting the images to stack at a shorter exposure go to the alignment tab and check how many stars are detected. Detecting too many stars is just as bad as not detecting enough. Too many stars and the alignment doesn't calculate. If you get alignment with your current settings at shorter exposure I'd lower digital gain down to 2x or off and see if you get enough stars.

-Chris

bemo47
Posts: 29
Joined: Sat Apr 21, 2018 12:06 pm

Re: No stacking with 120sec exposure and guiding

Post by bemo47 » Mon Jan 13, 2020 9:47 am

yes, ok, that make sense

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admin
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Re: No stacking with 120sec exposure and guiding

Post by admin » Mon Jan 13, 2020 7:11 pm

Hi,

Thanks for posting the screenshot – from the error I think it's fairly likely that no stars were being detected, but it looks like SharpCap isn't handling that situation correctly leading to the error text that is showing in the log window in your screenshot. I can correct that in the next version of SharpCap, but you will still need to try adjusting your star detection settings as mentioned above to get the alignment to work for you.

Cheers, Robin

bemo47
Posts: 29
Joined: Sat Apr 21, 2018 12:06 pm

Re: No stacking with 120sec exposure and guiding

Post by bemo47 » Mon Jan 13, 2020 9:18 pm

ok, done, by reducing digital gain to OFF, i can stack again !!!
i had also a warning for hot pixels, so i in,crease the minimum size of stars from 1 to 3 and its fine now, 120 stars used to align and it works perfectly.
Thanks again,
Bernard

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Re: No stacking with 120sec exposure and guiding

Post by admin » Tue Jan 14, 2020 7:18 pm

Hi,

That sounds good – normally digital gain would be a last resort for when stars are very faint. If you turn on digital gain with a bright background and bright stars it might make the whole image too bright (once the brightness is doubled or quadrupled) for the star detection to work properly.

Clear skies and hope you get some great images!

Robin

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