YsEVMeter reads the light through the iPhone camera and reports three exposure values at once — highlight, midtone and shadow — so you see the range of a scene, not just its average. Freeze a frame, place the spots where the tones you care about actually are, and the exposure calculator hands you the aperture and shutter speed to put them there.
It is built around the Zone System rather than bolted onto it. The three readings correspond to Zones VII, V and III; the Zone Map overlay posterizes the whole frame into the eleven Adams zones; and the Adaptive Zone control decides where the shadow and highlight boundaries fall — by percentile, by Otsu thresholding, or by hand.
Highlights
- Three readings, not one — highlight, midtone and shadow are metered together and labelled on the image, so the dynamic range of the scene is a subtraction you can do at a glance rather than a second measurement
- Zone placement you control — the Adaptive Zone picker sets the shadow and highlight boundaries by percentile (2%/98%), by multi-Otsu thresholding that finds the scene’s own tonal clusters, or by manual sliders
- Spots you can move — drag the three reticles to re-meter any point, or tap anywhere to drop a custom spot and read the EV there; tap it again to remove it
- Three overlays — a heatmap of brightness across the frame, a luminance histogram with the zone boundaries marked, and a Zone Map that posterizes the scene into the eleven zones
- Meter what you already shot — load a photo from the library and the app reads its EXIF aperture, shutter speed, ISO and date, then meters the frame the same way
- A full exposure calculator — ISO, aperture, shutter, ±EV, colour and ND filters in full, ½ or ⅓ stops, with aperture and shutter linked and your last manual choice preserved; bellows extension for large format, and reciprocity failure with a library of film presets
- Frame the format you are shooting — crop the preview to 35mm, APS-C, 6×6, 6×7, 6×9, 4×5, 5×7, 8×10 or a custom size, at the focal length and orientation you will use
- Calibrate to your meter — enter readings from a reference meter and the app fits a per-zone correction, so its numbers agree with the meter you already trust. Keep a separate profile per meter
- A shooting notebook — record a frame to a film roll or as a standalone memo, with the snapshot, its overlays, the spot positions, every exposure setting and, optionally, where you stood
Requires iOS 17 or later, on iPhone.
Everything is measured and stored on the device. There is no account, no analytics, and nothing is uploaded. Location is attached to a recorded frame only if you grant access, and it stays on the phone with the rest of the frame.