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Old 04-12-2008, 09:41 AM
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avandonk
avandonk

avandonk is offline
 
Join Date: Aug 2005
Location: Melbourne
Posts: 4,786
Before I built my fridge I worked out what was happening to the sensor temperature of my 5DH. When you turn the camera on it uses about four watts at idle and the sensor temperature goes up by about 2 deg C from ambient. When doing a long exposure the camera uses about eight watts and the sensor temperature then goes up by about 2 deg again. This takes some minutes to reach equilibrium.

You can measure the temperature of the sensor with one of those IR remote thermometers when the mirror is up.

If you have ever taken a sequence of exposure with ICNR from idle have a look at the first image and you will see 'holes' caused by the first 'dark' being taken at about 2C above the first 'light'. These holes are then much dimmer in subsequent exposures since the camera has reached equilibrium and 'darks' are at the same temperature as the 'lights'.

Turning the camera off between exposures is a waste of time as it takes many minutes for the camera to cool.

The only way to overcome these ambient temperature variation problems is to put the camera in a constant temperature environment. The fridge I built is temperature controlled within 0.1 C. This temperature can be set to any temperature 28 degrees C below ambient. So if the night starts off at 18C I set -10.0 C and in summer say -5.0 C or even higher on a very hot night.

I always take some test exposures for focus and start collecting data as soon as possible to stop the first exposure being 2 C cooler than the rest.

Bert
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