Noise: how much difference in temperature causes more noise?

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Menno555
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Noise: how much difference in temperature causes more noise?

Post by Menno555 » Sat May 23, 2020 8:58 pm

My camera is a Zwo ASI385MC, no cooling but it has a temperature read out.
How much more (or less) noise is there per 1 degree Celsius? For example, the sensor indicates 15 degrees C when I take Darks.
But after an hour it indicates 13 degrees C. Is it best to take new Darks then? Is there a general rule for that?

Thanks
Menno

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oopfan
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Re: Noise: how much difference in temperature causes more noise?

Post by oopfan » Sun May 24, 2020 5:45 am

Menno,

Manufacturers generally don't publish dark current figures for uncooled cameras because uncooled cameras are typically used for lunar and planetary imaging which use ultra-short exposures. Fortunately they do publish data for cooled cameras. We can gain some insight by looking at the dark current of the ASI1600:
ASI1600 Dark Current.jpg
ASI1600 Dark Current.jpg (68.95 KiB) Viewed 58 times
In the summertime it is not uncommon for your sensor to run at +25C or hotter. According to the graph the dark current is 0.5 electrons per second per pixel.

Dark noise is the square root of Dark current.

If your exposure is 4.5 seconds then your Dark noise is on par with your Read noise. That is, SQRT(4.5 * 0.5) = 1.5 electrons.

Dark noise increases with exposure but Read noise remains constant.

It is my personal experience that you will get better results capturing darks before lights while the sensor is warmest. I don't recommend capturing darks after lights. Some people advocate capturing 1/2 before and 1/2 after.

Dark noise is much less of a problem during winter months.

Brian

Menno555
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Re: Noise: how much difference in temperature causes more noise?

Post by Menno555 » Mon May 25, 2020 9:05 am

Brain, thanks!
I tried that methode of 50% Darks before and 50% Darks after. But then I have to use them in DeepSkyStacker and somehow that goes wrong. Doing everything that the DSS manual states for making Darks and Flats but when applying, I get totally screwed results. So using the SharpCap feature to make and use them. Works fine so far :)

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oopfan
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Re: Noise: how much difference in temperature causes more noise?

Post by oopfan » Mon May 25, 2020 2:21 pm

Menno,

I am glad you tried 50/50. Hmm, that's odd behavior out of DSS. Are the dark files in separate folders or did you move all dark frames into one folder before launching DSS? You ought to commingle the dark frames into one folder. The idea is that the master dark file that DSS creates will be created from frames at opposite ends of the temperature spectrum. The master is essentially the midpoint.

Brian

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