AF working range/detection range?

Started Sep 4, 2004 | Discussions thread
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gisle Senior Member • Posts: 2,468
Re: 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: .

There is a good explanation ov EV in the dpreview glossary, under "Exposure":

There is a somewhat simpler intro to EV at my IR resource page:

  • gisle

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