ShutterMeter

ShutterMeter times a mechanical shutter through the iPhone's microphone. It measures the gap between the opening and closing sounds and compares it with the selected speed, in stops. It covers 11 speeds from 1 s to 1/60 and does not measure faster ones. It rejects a reading when it can't tell which two sounds are the shutter. Three clear readings per speed build a health map for each camera. The app analyzes audio on the phone and doesn't upload it. The developer hasn't validated it against a hardware shutter tester. After 10 free results, a one-time purchase unlocks unlimited measuring.