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Weird black squared in my astro photo

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#1 wheelers4life

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Posted 08 December 2019 - 07:12 PM

Ok this is the veil nebula 10 stacked frames of 10 min.  20 dark frames, 20 light frames gain at 310 raw 16 I stacked them in deep sky stacker. When I loaded the image in pixnsight and used the screen transfer function to stretch using the radioactive icon. When I zoom in I get these black squares. Have anyone encountered this. I went back an looked at other images and some have them and some do not. any ideas why this would happen. The attached pic is of the zoomed in pic to see the black squares. 

Thanks

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#2 OldManSky

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Posted 08 December 2019 - 07:14 PM

This usually happens if:

a) your offset wasn't high enough, and/or...

b) your darks don't match your light frames (for temperature, gain, offset, and time).

 

Make sure you aren't using the option to scale/optimize dark frames as well.


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#3 wheelers4life

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Posted 08 December 2019 - 08:08 PM

Dang when I take my darks. I take them right after my lights. I do not change anything except shut guiding off

#4 Scott Mitchell

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Posted 08 December 2019 - 08:14 PM

What camera are you using? Is it cooled? If so you should be able to build a dark library independently of shooting lights.Then just pulled the appropriate temperature darks when you're ready to stack.



#5 OldManSky

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Posted 08 December 2019 - 08:45 PM

So if your darks match your lights in all settings, then...what was your offset?

And did you have scale/optimize dark frames "on" when you stacked them?

 

What software are you using for capture and stacking/calibrating?



#6 wheelers4life

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Posted 08 December 2019 - 09:10 PM

I'm using a zwo 294mc pro cooled to -10. I'm using sharpcap. I'm new to all this so I do not know what offset is.
My process is. Turn on sharpcap and center Polaris. Attach my mask and focus. The do a polar alignment with sharpcap. Then open cpwi and align scope. Find my target and do sample exposures until it is to bright then bring my subs down a bit. While this is going on I make sure my color balance is set right. Blue and red are peeking at the same point. Then take my light frames. When they are finished I put my cover over the scooe and take my dark frames. Then take some fast dark frames for bias. Then put the cover off. Place a white t shirt over the scope and turn on my light board and place it on the scope and take some fast flat frames.

#7 wheelers4life

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Posted 08 December 2019 - 09:11 PM

I use deep sky stacker to stack, pixnsight and photoshop to process. This only happened to a few of my images.

#8 gezak22

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Posted 08 December 2019 - 09:49 PM

Even when your darks are perfectly matched to your lights, you should be dithering your exposures so that dead pixels and hot pixels end up at different locations (relative to the stars) and their extreme values can be rejected and replaced by actual data (from subs when the dead/hot pixels landed elsewhere).

 

If this makes no sense, just try a session where you dither every shot and compare the sky background in the resulting image to that from previous images.



#9 wheelers4life

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Posted 08 December 2019 - 10:44 PM

Ok is this dithering set up in sharpcap while imaging


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