Install
Get YsEVMeter from the App Store. It requires iOS 17 or later and runs on iPhone, in portrait.
On first launch the app asks for camera access. Tap Allow — metering the live scene is what the app does, and it cannot do it without the camera. If you tap Don’t Allow by mistake, turn it back on in Settings › YsEVMeter › Camera.
Location access is asked for separately, and only when you first record a frame. It is optional: decline it and everything works except the coordinates attached to a recorded frame.
1. Point it at the scene
The app opens in Live Mode. Three reticles float over the preview and track the scene as you pan:
| Reticle | Colour | What it is on |
|---|---|---|
| High | Red | The brightest region — Zone VII |
| Mid | Green | The middle tone — Zone V |
| Shadow | Blue | The darkest region — Zone III |
Each carries its EV, and the readout below repeats all three. The gap between the High and Shadow numbers is the dynamic range of the scene in stops — the number that tells you whether your film can hold it.
2. Set ISO and format
Two controls change what the readings mean:
- ISO — set it to the film you have loaded. Doubling ISO adds 1.0 EV to every reading, so a wrong ISO makes every number wrong by the same amount.
- Film format — pick the frame you are shooting (35mm through 8×10, or custom) and the focal length. The preview crops to that format’s angle of view, so what you are metering is what the camera will see.
3. Freeze the frame
Tap the shutter button. The camera stops, the frame freezes, and the app enters Offline Mode with the full set of tools. Nothing is written to your photo library — the snapshot lives in the app until you leave offline mode.
To meter a photograph you have already taken, tap the photo button instead and pick one from the library.
4. Place the tones
In offline mode the readings hold still, so you can put them where you want them:
- Drag the High, Mid or Shadow reticle onto the thing you actually care about. A spot you drag is marked Manual; Reset returns it to the automatically detected position.
- Tap anywhere else to add a custom spot and read the EV there. Tap it again to remove it.
- Change Adaptive Zone — 2%, Otsu or Manual — to move where the shadow and highlight boundaries sit.
Turn on the Zone Map (V) overlay to see the whole frame posterized into the eleven zones. It is the fastest way to check that the tone you metered is on the zone you meant.
5. Read the exposure
Scroll down to the exposure calculator. The EV field shows the metered midtone; below it, aperture and shutter speed are linked, so setting one moves the other and the exposure stays put. Set the aperture you want, read the shutter speed. Add a colour or ND filter, bellows extension or reciprocity correction and the numbers follow.
6. Keep the frame
Tap Record to log the exposure — to a film roll, or as a standalone memo. The app saves the snapshot with its heatmap, histogram, zone map, spot positions, EV readings and every setting you used, so after the film comes back you can compare what you metered with what you got.
Where to go next
- Live Mode — the controls on the camera screen, and what metering mode changes.
- Offline Mode — spots, adaptive zones and the three overlays in full.
- Calibration — making the app’s numbers agree with your reference meter.