Test your film camera's shutter
ShutterDoc measures how long your film camera's shutter really stays open, using your iPhone. It is free to download.
Shutters wear out. If you set the dial to 125 on an older camera, it might hold open for a hundredth of a second instead, with seemingly nothing amiss. ShutterDoc films the shutter at 240 frames a second and measures the light that comes through, telling you how truthful your camera's shutter speeds really are. Because it measures light rather than timing the shutter, it can read an exposure shorter than a single frame.
There are two ways to test speeds. The Quick Test is free. It can be performed handheld, in normal lighting conditions, and requires minimal setup. Point the phone, fire the shutter, and see each speed from 1 second to 1/60 on focal plane shutters, or to 1/125 on leaf shutters. It is quick enough to check a camera at a flea market before you buy it. The Full Test, part of ShutterDoc Pro, measures every speed from 1 second to 1/1000, or to 1/500 on a leaf shutter, with the camera steady on a tripod or a stack of books, in an even light.
Both work on focal plane shutters, the kind in most SLRs and rangefinders, and on leaf shutters in the lens. ShutterDoc's readings have been checked against a dedicated phototransistor tester on six cameras of both kinds: a Nikon FE, Canon EOS-1N, Minolta X-370, Kiev 19, Tele-Rolleiflex and Kodak Retina.
For focal plane shutters, ShutterDoc Pro also has a capping test. Rather than a speed, it shows how evenly the light lands across the frame, and whether one band of it is getting less light than the rest. Fire the camera at least ten times at one speed, as fast as 1/1000, and ShutterDoc averages the firings into one map of the light across the gate.
You need an iPhone on iOS 17 or later that films slow motion. ShutterDoc is built for 240 frames a second.
ShutterDoc does not replace a workshop-grade tester. Flickering light, or a small change in the light or the filming angle, can move a fast reading, and the app says when it doubts one.
The measurement happens on your phone. There is no account, and your video is never uploaded.
See how a test is done, on video.
Free, with one purchase for the rest
Without buying anything you get the Quick Test, any result shared as an image, and your last five quick tests kept to open again.
ShutterDoc Pro is one in-app purchase. It adds the Full Test to 1/1000, the capping test, and My cameras: each camera with its shutter type, flash sync and notes, every test kept to compare over time, export to a spreadsheet, and backup to one file.
Bought ShutterDoc before it was free? You already have ShutterDoc Pro, with nothing to buy. If anything shows a lock, tap it and choose Restore purchases.
Get ShutterDoc free on the App Store, for iPhone.