AF working range/detection range?
Carl Snyder wrote:
What determines a camera's ability to focus in low light? I
noticed that the 20D has a rating of -0.5 to 18, while the 1DII is
rated at 0 to 18. The detection range of the nikon cameras is -1
to 19. What do these numbers mean and what determines them?
These are EV numbers and they are a convienent way to indicate absolute light levels without going into ISO, apertures and shutter speeds.
EV 0 to -1 are "subjects lit by dim ambient artificial light", according to Fred Parker's EV chart: http://www.fredparker.com/ultexp1.htm .
There is a good explanation ov EV in the dpreview glossary, under "Exposure": http://www.dpreview.com/learn/?/Glossary/Exposure/Exposure_01.htm
There is a somewhat simpler intro to EV at my IR resource page: