ShutterDoc: Shutter Speed Test

Measure what your film camera's shutter is actually doing. ShutterDoc measures shutter speeds in ordinary room light.

Take the lens off, open the back, point the phone into the mount and fire. A run from 1/30 to 1/500 on an SLR, three firings a speed, takes about two minutes. A test roll costs you the film, the developing and a fortnight of waiting, and still leaves you guessing which speed was off.

You can also detect shutter capping for speeds up to 1/1000th of a second.

WHAT IT DOES

Measures speeds from 1 second to 1/500, on focal-plane shutters, so most SLRs and rangefinders, and on leaf shutters, so folders, TLRs and fixed-lens compacts. Separate guidance for each.

Detects shutter capping. It maps the exposure across the whole film gate and finds bands that received little or no light, on horizontal and vertical shutters alike.

Puts a confidence on every reading, and says when conditions will not support a number you can trust.

Keeps a library of your cameras, with shutter type, flash sync and notes, tested or not, and saves every session so a body can be compared over time.

Exports readings and capping maps as CSV, for a repairer or a buyer.

Walks you through the setup the first time you open it.

WHAT IT IS FOR

Buying. The seller says the speeds sound about right. Check before the money changes hands, at a flea market or across a cafe table.

Shooting. An old leaf shutter can be well off its markings at the slow end. Measure it once and expose for the real number rather than the marking.

Selling. Show a buyer the numbers rather than asking them to take your word for it, and put the export in the listing.

A shelf of them. Work through the bodies you never tested and find out which are honest.

Servicing. Test it, send it off, test it again, keep both sessions.

CAPPING DETECTION

At fast speeds a focal-plane shutter exposes the frame through a moving slit. If the curtains drift out of step the slit closes partway across and a band of every photograph receives nothing. Rest the camera on a tripod, fire about ten times one speed, and ShutterDoc averages them into one map of the light across the gate. It answers in one of four words, even, uneven, unsure or capping, and says unsure rather than picking the nearest when the evidence will not carry one.

ACCURACY

Verified against a phototransistor rig built for the purpose, on a Nikon FE, Minolta X-370, Canon EOS-1N, Kiev 19, Kodak Retina and Tele-Rolleiflex: horizontal and vertical focal-plane, and leaf.

1 second to 1/30: typically within 5% of true speed.
Leaf shutters: typically within 0.15EV as far as 1/125.
Focal plane at 1/125 and 1/250: usually within 0.3EV.
1/500: usually within 0.5EV, almost always within 0.6EV.

Handheld is fine at 1/60 and below, which is what quick test mode is built for. Above that you want a constant, diffused light source, a monitor at full brightness or a wall with indirect sun on it, and a tripod if you have one. The app explains the setup and carries the full table.

WHAT YOU NEED

An iPhone that shoots 240fps slow motion. A camera whose lens comes off and whose back opens, with no film in it. Fixed-lens leaf-shutter cameras work too, at their widest aperture. A bright wall or a monitor at max brightness is enough light.

HOW IT WORKS

The phone films the shutter at 240 frames a second and adds up the light that reached the film gate, which is what your film would have received. Measuring light rather than timing an event is what resolves an exposure shorter than one frame.

PRIVACY

Your video is never uploaded. The measurement runs entirely on your phone. No account, no sign-in, no tracking.

LIMITS

ShutterDoc does not replace a workshop-grade tester, and small changes in lighting or filming angle can move a fast reading. Published accuracy results come from internal testing under controlled conditions, and your own may differ with your camera and your light. Get in touch if something is not working.

Filming

• A full test on a focal-plane camera is now filmed from behind: back open, lens on at its widest aperture and pointed at your light, in a dark room. Only light that came through the lens and the shutter reaches the phone. A quick test, and capping, are still filmed from the front with the lens off. Leaf shutters are filmed from behind for both tests.
• Filming from behind, hold the phone upright or sideways, whichever is more comfortable.
• Before each test, a short card shows how to set up the camera and the phone. The setup screen and the recording screen both say which side to film from.
• If you have used ShutterDoc before, a short note explains the change the first time you open it.
• The setup guide is shorter, explains the two tests first, and has a new drawing for filming from behind.

Focal-plane shutters

• At the flash sync speed and slower, from 1/60 down, each reading now times every part of the frame on its own, so light that changes during a long exposure no longer throws it off. With no flash sync entered, this starts at 1/30. If the light reading disagrees, the reading says so.
• Fixed: in dim light, speeds around 1/8 and slower could read far too short, with a "Mirror light removed" note. Noise in a dim picture was being taken for light from the mirror.
• A quick test can now measure the sync speed itself with no slower shot: 1/60 on a camera that syncs at 1/60, 1/30 on one that syncs at 1/30. Enter the flash sync on the setup screen.
• A full test now needs a slow speed to measure the faster ones against: 1/30 on most cameras, slower on one with a slow flash sync. It starts ticked, and you can swap it for any slower speed.
• A gate a little off square no longer brings up a "Camera tilted" warning.

Setting up

• The setup screens are shorter. What to do stays on screen; the reasons are behind the ⓘ buttons.
• Capping opens with a short "Before you start" card, including which way to hold the phone. The example maps have a colour scale, and Saved runs is at the top of the screen.

Other

• When a test on one of your cameras is finished, closing the readings takes you to that test on the camera's page.
• Exports now include the frame rate each reading was filmed at.