ShutterDoc Checks Whether Your Film Camera Tells the Truth

Field notes

The proposed workflow uses iPhone video at 240 frames per second, then measures the light passing through a camera shutter to report its actual duration. It covers both focal-plane shutters, common in SLRs and rangefinders, and leaf shutters built into lenses. A separate capping test is identified as beta; it evaluates uneven exposure across the frame rather than returning a shutter-speed number. The site states that recordings remain on the phone.