Last week, I was blogging about exiftool’s newest tag discovery, the CameraTemperature. I assumed that the CameraTemperature roughly equals the environment temperature and sketched some really exciting applications based on this idea (e.g. assigning keywords or conducting searches using this tag).
Unfortunately, some open questions remained: I couldn’t evaluate my assumption, because I don’t own a PowerShot. Another interesting, yet unanswered question is how quickly the CameraTemperature adapts to the environment temperature. Luckily I spend this weekend at my mother’s house and could conduct the necessary tests with her Powershot A2000 IS.
My test setup
My test setup was fairly simple: turn on the Powershot for 5 minutes and take a picture to my digital thermometer every 20 seconds. I planned to conduct this procedure inside my appartment (approx. 24 degrees Celsius room temperature) and outside (approx. 3 degrees Celsius). Before running my tests I allowed all devices an acclimation time of 10 minutes. I deliberately choose this period to be rather short, because I wanted to test how fast the CameraTemperature adapts to a changing environment temperature (think of quickly leaving your warm room to take some pictures of the snowman the kids have built).
Although the Powershot A2000 IS is just pocket size, I didn’t put it in my jacket to avoid any accidential heating by my body.
Interior Test
The interior test ended quite promising: I took 15 pictures, the first 7 yielded a camera temperature of 20 degrees, the other 8 of 21 degrees. My thermometer was showing constantly 23.3 degrees. Wow! This means just a difference of 2-3 degrees.
The thermometer reports 3.7 degrees celsius, but the CameraTemperature yields 18 degrees for this picture.
The disappointing Exterior Test
The exterior test caused more headaches (not just because of the cold October 
). Even after the acclimation period of 10 minutes, my reference thermometer was still showing the interior temperature of 23.3 degrees. When I “rebooted” it by removing the batteries, the temperature first dropped down to 8, then to 3 degrees. This was the accurate temperature according to the local weather report.
However, for my total 20-minutes-stay outside, the camera temperature never dropped below 17 degrees. Quite far away from the 3 degrees actual exterior temperature.
This diagram shows the slow acclimation time for the CameraTemperature. Coming from a previous interior temperature of 23.7 C, it was exposed to an exterior temperature of 3.7 C for 10 minutes. After that, numerous shots were taken at the same temperature. The points indicate the recorded CameraTemperature for each shot. After 20 minutes, the CameraTemperature just dropped to 17C
Conclusions
The results from the exterior test seem to indicate that the camera needs a long acclimation time until its temperature reachs the external temperature. In my tests, the temperature dropped by just 5 degrees in the first 20 minutes, which equals to 25% percent of the total temperature difference of 20 degrees. If we assume a linear progression, the camera needs to be exposed at least for 4*20 = 80 minutes to an environment until its temperature equals the environment temperature.
