Shutter Actuation Count
The running total of exposures a camera's mechanical shutter has made, recorded in the file metadata.
Measured in
count
In depth
Mechanical shutters are rated for a life expectancy — typically 100,000 cycles on an enthusiast body and 400,000 or more on a professional one — though these are statistical averages rather than expiry dates. The count is the main measure of wear when buying used, in the way mileage is for a car, and it is read directly from the EXIF of a recent file.
Examples in practice
A used body advertised at 32,000 actuations against a 300,000-cycle rating has used roughly a tenth of its expected life.