What is the ISO equivalent (film speed) of the human eye?
This is one of those “no clear answer” type questions. The eye is truly amazing in some ways, but limited in other ways. It has no zoom function, no telephoto ability. It also only has high spatial resolution in the fovea, and the brain basically stores or constructs most of the image. In low light, the central fovea basically stops working. The remaining rods can only see black/white at low spatial resolution (compared to the fovea). If you were to build a wide-field (short focal length), fixed (no zoom ability), and a high-quality black/white CCD with high quality noise reduction algorithms, I’m fairly confident you could approach the ISO performance of the human eye. I think because there’s a bit of “apples vs oranges” problem here, it is difficult to give a single ISO equivalent, and google searches show guesses anywhere from 800 to 60,000 ISO (ie., probably no one knows for sure).
