I was recently reading the article The Truth about Digital ISO in Digital PhotoPro magazine, and decided to investigate the camera sensor noise profile of the Canon Powershot G12 I use for underwater photography.
Noise plays a big part in underwater photography. Available light levels are lower underwater,with less available the deeper you go. Knowing the noise performance of your camera allows you to push the ISO and get maximum performance.
I started looking at noise in the Canon Powershot series of cameras in my previous post Noise Comparison – Canon Powershot G11 vs G10.
There has been some recent talk on the web about “native ISO”, where the lower ISO of a camera is not necessarily the best for noise performance due to in-camera amplification methods. I have always thought the underwater photos taken with my Canon G12 at ISO160 were better than ISO80 or ISO100, and thought this might have been the effect of native ISO.
After reading the article The Truth about Digital ISO in Digital PhotoPro magazine, I decided to test my theory.
I setup the camera in manual mode, with a shutter speed of 1/60 sec, aperture of f2.8, and fixed white balance. A fixed white balance is required so the camera does not try and change the colour tints of the high ISO noise, giving you an incorrect result.
I placed a filter barrel and cap over the lens to block out all light, and shot a sequence of RAW images at different ISO settings from 80 to 3200.
The first interesting thing I noticed was the size of the RAW files.
The size of the file increased as the ISO increased with more sensor noise. The ISO3200 RAW file is nearly twice the size of the ISO80 file.