Finding the ISO of the Human Eye
People often draw the comparison between a camera and a human eye. It's a flawed metaphor, especially with digital cameras which act as part-eye and part brain, but a compelling one nonetheless.
The folks over at Pixiq have posted an interesting article comparing the photographic process with the one that the human eye goes through. In most cases, the human eye is superior. It adjusts for the light, autofocuses at incredible speed and even helps to clean up blurs. In the camera's corner is the lack of a brain, which means there's nothing to trick.
One of the most interesting parts of the article is the attempt to pin down the ISO of the human eye. The answer is complicated and well worth a read.