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Just your iPhone and a scene to meter. Zone Meter uses the rear camera to read ambient light — no accessories required. iOS 16 or later is needed. A real device is required; the Simulator has no camera.

Use the Av / Tv / ISO selector on the Meter tab.

Av (Aperture Priority) — you set the aperture and ISO on the drum wheels; Zone Meter calculates the correct shutter speed.

Tv (Shutter Priority) — you set the shutter speed and ISO; Zone Meter calculates the aperture.

ISO Priority — you set aperture and shutter speed; Zone Meter tells you what ISO you need.

The computed (locked) column is highlighted and auto-scrolls as the light changes.

Tap anywhere on the live camera preview. Zone Meter moves both the focus point and the exposure point to that location — you'll see a yellow square appear briefly at the tap point. The EV and all computed values update to reflect that specific area of the scene.

Select your ND filter from the grid (or enter a custom stop value), then choose whether to use the live meter reading as your base shutter speed or pick one manually. Zone Meter multiplies the base exposure by 2^stops to give you the long-exposure shutter speed. If the result exceeds 30 seconds, it reminds you to use Bulb mode.

Hyperfocal distance is a fixed optical property of your lens, aperture, and sensor format — it does not depend on where your subject is standing. It is the focus distance at which everything from half-hyperfocal to infinity is acceptably sharp.

What does change as you move the slider are the near focus limit, far focus limit, and total depth of field — these describe the sharp zone when you focus on your subject at that distance.

The Strobe tab uses the guide number formula: f = GN / distance. Select your strobe from the presets (or enter a custom guide number), choose your power setting, and set your ISO. Zone Meter calculates either the aperture you need (Aperture mode) or how far to place the strobe (Distance mode). The fill light ratio calculator shows you the aperture for a second light at any ratio from 1:1 to 16:1.

Tap the Save button in the top-right of the Meter tab, or the Save button in the Strobe tab header. A sheet slides up showing the current reading — type a name (like "Window light, morning" or "Studio key at f/8") and tap Save. Your reading appears in the History tab.

Yes. In the History tab, swipe left on a reading for Share and Delete. Swipe right to edit the name and notes. You can also use the trash icon in the top bar to clear all readings at once.

Go to the Help tab. At the top of the screen, under Preferences, tap the m / ft toggle. The change applies immediately to all distance displays in the DoF and Strobe calculators.

"Waiting…" means the camera session is still initialising. This usually takes 1–2 seconds on first launch. If it persists, check that Zone Meter has camera permission in Settings > Privacy & Security > Camera. The dot in the top-right turns green when the camera is live.