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Bright spot on dark frames.

CMOS Beginner Astrophotography
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#1 Foofy

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Posted 25 July 2021 - 05:49 PM

Hi all,

I’m new to AP and after briefly looking at some of my dark and light frames, I’ve noticed a bright almost star diffraction spike looking light on some of my darks and lights. Not sure what’s causing it, but I think it could have to do with leaking light from my filter drawer (but I don’t see how this could show up on my darks since I take them in a pitch black room). Anyway, I’m wondering if anyone has an idea on what the culprit is.

Here’s what I am shooting with:
William Optics Zenithstar 81 with 0.8x reducer and flattener, ASI294MC-P with a 2” ZWO filter drawer, and an Optolong L-enhance filter.

#2 Foofy

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Posted 25 July 2021 - 06:03 PM

Here's an attachment of one of my dark frames. Exposure: 360 seconds, Temp -10 C, Gain 120.

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  • IMG_0215-min.jpg


#3 Sky Muse

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Posted 25 July 2021 - 06:09 PM

I'm seeing light creeping in from both sides, from top to bottom; however none from the top and bottom, from the center outwards. 



#4 alphatripleplus

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Posted 25 July 2021 - 06:14 PM

It's amp glow which will appear in both raw light and dark frames with many CMOS sensors. When you calibrate your light frames (by subtracting) darks that are matched with the lights in terms of  gain, temp and exposure, the calibrated lights should be free of amp glow.


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#5 Foofy

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Posted 25 July 2021 - 06:59 PM

Got it. So as long as I am taking calibration frames, it shouldn’t matter.

#6 alphatripleplus

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Posted 25 July 2021 - 08:18 PM

Yes, dark subtraction will remove amp glow from your lights.




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