Temperature Curve of long time exposure [Unmodified EOS 350D(Rebel XT)]

▣ The rise of the temperature of image sensor according to exposure time   [unmodified original 350D(Rebel XT)]

data: Canon 20-35L lens,
EOS 350D(Rebel XT)
      ambient air temperature:75℉ (24 ℃)
ASA1600, 15min exposure &
3min rest & 5min exposure

We have checked temperature change with B shutter exposure by attaching thermometer on the back surface of CMOS Sensor.

A chart above shows that the temperature rises in proportion to the exposure time. When 15 minutes exposure was finished the temperature reached 86.5℉(30.3 ℃) with a rise of 11.5℉ (6 ℃). After 3minutes rest we made 5 minutes exposure with the same camera setting. The temperature was dropped 0.5℉ (0.3 ℃) after 3minutes’ rest but with the exposure that was rose again and reached 88℉ (31.3 ℃).

These images below were cropped from original full size images.

Large file (100%)☞

In the case of multiple shots for composition, because the rise of sensor temterature, each of images didn’t have same noise level. The images taken later had more noise. This fact makes darkframe image processing more difficult work.
If you are interesing good quality, you need to either take pictures with a sufficient interval or take pictures with a proper cooling system.

Images below are reduced comparison of pictures above with the those taken by Astro 350D.