Low-light AF Rating
The dimmest light level at which a camera's autofocus is specified to work, quoted in EV at a stated aperture and ISO.
Measured in
EV
In depth
Figures are only comparable when the stated conditions match, since a rating measured with an f/1.2 lens flatters a camera against one measured at f/2. Ratings around −4 EV cover a candlelit room; −6 EV approaches the light of a moonless night sky, where the eye itself sees almost nothing.
Examples in practice
A body rated to −6 EV with an f/1.2 lens can autofocus on the Milky Way, where a −3 EV body must be focused manually.