If you’ve been using a manual film camera and can’t figure out why some of your photos turned out over or underexposed, chances are the shutter isn’t firing at the speed your camera says it does. To fix this, you have two options: either send it for a repair that’ll most likely last weeks, maybe months, or get yourself a lie detector called the Filmomat PhotoPlug. Once you know the real numbers, you can adjust your shutter speeds accordingly.
The PhotoPlug is a small device that connects to your phone via a 3.5mm audio plug and measures the shutter speeds your camera is actually delivering. Filmomat also makes the app, aptly named Shutter Speed. You can download it for free on iOS and Android.
Since I already have three manual film cameras, I wanted to see how different the real shutter speed is from the one on the dial. I’ll walk you through the entire process and show you the results along the way.
Setting up the PhotoPlug and the app
Getting started is straightforward. Open the back of your film camera and remove the lens. Then place a source of light in front of the lens mount, shining onto the curtain. A phone’s flashlight is enough for this.
Connect the PhotoPlug to your phone using its 3.5mm plug. If your phone doesn’t have an audio jack, you’ll need an adapter. This is where it’s worth paying attention: Filmomat warns that many USB-C to audio or Lightning to audio adapters won’t work with the PhotoPlug, so they sell their own, which works reliably. If you’re still using an older phone with a built-in audio jack, you’re already set and can skip the adapter altogether. The app also runs on tablets, which helps, since most tablets, unlike phones, have kept the audio jack.
Once connected, position the PhotoPlug facing the open back of the camera, aimed at the shutter curtain. Open the Shutter Speed app and add your camera to the Camera Manager section. Add all your cameras here before you start testing; it makes the rest of the process faster.
Recording the shutter speeds
Once you’ve set up your camera and the app, recording is simple. Set the shutter speed on your camera. Then press the aperture symbol in the app to start capturing. Fire the shutter, and wait for the result to appear. Once it does, select the target speed from the button in the bottom left corner, then hit Save Measurement in the top right. The app shows the saved camera list; select the camera you’re testing and press Save. Repeat this for every shutter speed your camera can do.
One thing worth pointing out: the app can only save measurements for speeds between 1/1s and 1/500s. It can still record faster speeds, like 1/1000s, but won’t let you file them into the table alongside the rest.
After you’ve gone through all the shutter speeds, head back to the Camera Manager section to see the full set of results for that camera.
The results
Before getting into the numbers, it’s worth explaining the Correction column: it shows how much exposure compensation you’d need to apply, expressed in thirds of a stop, to make up for the gap between the target speed and the shutter’s actual output. Note that the Zenit 11’s table has no data for speeds slower than 1/30, since that’s the camera’s slowest setting.
Looking at all three cameras, a pattern shows up: every camera loses accuracy as the shutter speed increases, though not by the same amount. The Minolta CLE holds up best, never drifting more than two-thirds of a stop off target, even at 1/500. The Zenit 11 and the Pentacon Six TL both fall off more steeply at the faster end. The Pentacon Six TL is the most extreme case: at 1/250 and 1/500, it needs a correction of 1 stop and two thirds, meaning the shutter is running far slower than the dial claims, and anything shot at those speeds would come out noticeably overexposed.
Since neither app table includes a 1/1000s row, I’ll mention them next. The Minolta CLE, when set to 1/1000s, actually fires at roughly 1/1100s, only a minor deviation. The Pentacon Six TL tells a different story: at the same 1/1000s setting, it fires at roughly 1/370s, a third of what’s supposed to do, and in line with the 1/250s and 1/500s speeds.
As the numbers started drifting noticeably from the marked speeds, I repeated several tests to make sure I wasn’t looking at a fluke. The results held up, with only small variations between runs. Testing the Pentacon Six TL’s 1/1000s setting three times, for example, returned 1/364s, 1/373s, and 1/367s, confirming the camera is consistently firing at roughly a third of its intended speed rather than the reading being a one-off error.
Recording without the PhotoPlug
The app can also measure shutter speeds using just your phone’s microphone; you don’t need the PhotoPlug for this. It’s a fine option if you only need to check a speed once. I wouldn’t recommend it if you’re testing multiple cameras and want to build out full tables of results. The whole experience feels lacking.
The difference shows up right away in the waveform. I tested the same Minolta CLE at the same 1/60s speed, and the microphone recording came out far noisier than the PhotoPlug’s clean signal. That makes it harder to tell where the shutter actually opens and closes. Setting the start and end points becomes cumbersome as a result, and the pinch-to-zoom feature, which should help with precision, feels clunky instead.
Should you buy it?
If you’re happy with your camera and getting predictable results when setting shutter speeds, then you don’t need the PhotoPlug. If you have multiple film cameras, or you’re about to buy one and have agreed with the seller to run a shutter speed test first, it might be worth spending €44.90 on it. Keep in mind that the price is for the PhotoPlug alone, if you need one of Filmomat’s adapters, the USB-C version brings the total to €54.90, and the Lightning version to €69.90. For me, it helped a lot with adjusting expectations, especially from the Pentacon Six TL.
