Auto ISO
A camera mode that lets the body select sensitivity automatically within limits the photographer sets, usually with a minimum shutter speed.
Measured in
ISO
In depth
Properly configured, Auto ISO turns manual mode into a semi-automatic system: the photographer fixes aperture for depth of field and shutter speed for motion, and the camera varies only the least damaging of the three. The important settings are the ceiling — beyond which noise becomes unacceptable — and the minimum shutter speed, which many cameras can tie to the focal length in use.
Examples in practice
A wedding photographer sets f/2, 1/250 s, Auto ISO 100-6400, and shoots an entire reception without touching another dial.