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OSC Cooling?

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#1 claws

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Posted 24 September 2021 - 07:38 PM

I have a ZWO ASI294 and have noticed many people cool these cameras to -10 C or lower before imaging. What is the reason for this? It would seem that cooling the camera to 0 degrees C would be sufficient since that is the temperature that water freezes. I must be missing something here. 

 

Thanks,

Kim


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#2 Jim Waters

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Posted 24 September 2021 - 07:47 PM

There's less read and background electronic noise in the image with lower temperatures.  Look at the dark current graph below - electrons per second per pixel..  When I can I cool my ASI2600MC Pro to -10c and sometimes lower.  A dew heater keeps the window free from frost and the sensor camber has desiccant packs to keep the humidity down.  Cooling increases dynamic range.

 

https://astronomy-im...294mc-pro-color


Edited by Jim Waters, 24 September 2021 - 07:50 PM.

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#3 Rac19

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Posted 24 September 2021 - 08:22 PM

The lower the sensor temperature the less noise, especially for longer (DSO) exposures. I think that cooling is even of some benefit, though not essential, for planetary imaging, allowing (I think) the gain to be increased to set shorter exposure times, for "lucky imaging".

 

Going below zero doesn't in itself mean that dew will form, although air can carry much less water at 0 and below than at "normal" temperatures. As mentioned above, cooled cameras have various precautions to counter dew formation such as dew heaters (ironically) and desiccant tablets.

 

EDIT: An often stated benefit of cooling fir DSO imaging is that it allows for lights and darks to be exposed at a constant/controlled temperature,


Edited by Rac19, 24 September 2021 - 08:26 PM.

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#4 claws

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Posted 24 September 2021 - 08:53 PM

Thanks for this info guys. The dark current vs temperature graph shows the need for sub zero temperatures quite well.

 

Kim



#5 barbarosa

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Posted 24 September 2021 - 09:32 PM

At least a few ASI 294 owners, myself included, have discovered that on some nights cooling below about 0C creates localized freezing in the sensor. This can manifest as random dots in the image or streaks resembling a blurred fingerprint. When you raise the set point from below 0C to say 1 or 2C you can watch these dots and lines fade and vanish.

 

I now set the cooling on my 294 and the dots no longer appear.

 

ZWO diagnosed the problem as moisture in the camera and after some back and forth and various do this try that suggestions they t replaced it.

 

A few months later the spots returned but raising the set point solved it well enough for me.


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#6 claws

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Posted 25 September 2021 - 09:03 AM

At least a few ASI 294 owners, myself included, have discovered that on some nights cooling below about 0C creates localized freezing in the sensor. This can manifest as random dots in the image or streaks resembling a blurred fingerprint. When you raise the set point from below 0C to say 1 or 2C you can watch these dots and lines fade and vanish.

 

I now set the cooling on my 294 and the dots no longer appear.

 

ZWO diagnosed the problem as moisture in the camera and after some back and forth and various do this try that suggestions they t replaced it.

 

A few months later the spots returned but raising the set point solved it well enough for me.

I think that APT has an incremental cooling option that is supposed to address this problem. Don't know how well it works since my first attempt at imaging last week was a total failure. I was totally unprepared on just about every level.




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