The DSLR sensors do return a signal even in complete darkness. This signal is due to the thermal movement of the electrons. The atoms, excited by the heat, are expulsing some electrons from time to time, the heater the merrer. These electrons are then analysed by the DSLR electronic such as the "real" electrons generated by the photons. This current is called the "dark current". It is proportional to the exposure time and increases with the temperature.

A common rule of the thumb says that the dark current doubles every 6 to 8 °C. This article tries to measure the law of the Canon EOS 1000D sensor.

Key word : Canon EOS 1000D, dark current, temperature

1. Preparation

Take about 60 photos in the complete darkness (400 ISO, 300 seconds). Place the camera under a pillow to let it heat up, then if a fridge and a freezer to let it cool down. By doing this, I was able to shoot pictures from 0°C to 40°C.

The EOS 1000D records the temperature into the EXIF data. I used Exiftool to recover it.

The pictures were then analysed with Iris from Christian Buil in order to substract the offset (made from 32 pictures) and to remove the dead/hot pixels.

2. Conclusion

I found that the rule of the thumb is accetable to explain the dark current of the 1000D sensor, the dark current doubles when the temperature increases by 6.5 °C.