Light Meter

A real-time light meter that’s always in your pocket. Point your phone at a scene and read the light straight off the camera — the exposure value, and the aperture, shutter and ISO that go with it — before you ever unpack the rig. Tap around the frame to meter the shadows and the highlights, see the scene’s whole tonal range on a Zone-System ruler, and place a tone exactly where you want it. It’s the fastest way to compare the light between two spots, judge a high-contrast scene, or settle on a starting exposure while you’re still deciding where to stand.

A reference meter, not a calibrated instrument. Your phone isn’t a lab-grade incident meter, and its sensor and lens aren’t your camera’s. So the Light Meter is built to be internally consistent — brilliant for comparing zones and scenes and getting a confident starting point — rather than claiming an absolute, calibrated reading. If you want it to match your camera or a handheld meter exactly, you can calibrate it once (see below).

Everything on this page is what the meter does on iPhone. The Light Meter is coming to Android too, and much of it will be there — reading the light, spot metering, the Zone System, the histogram and colour readouts, and the zoom. Camera profiles, calibration, film reciprocity, freezing a frame, saving a reading and the built-in walkthrough will all be there too. Here’s exactly where it stands.

What you get

• Live exposure, read from the scene. Aim at the scene and the meter shows the exposure value (EV) it reads, updating as the light changes. It’s read from the camera’s own metering, so there’s nothing to dial in to get a number.
• Aperture or Shutter priority. Pick which side of the exposure triangle you want to hold fixed. In Aperture priority you set the aperture and ISO and the meter solves the shutter; in Shutter priority you set the shutter and ISO and it solves the aperture. The solved value updates live and is highlighted so you always know which one the meter is choosing for you.
• Spot metering — tap the tones that matter. Long-press anywhere on the live view to drop a metering pin. Drop a few — one in the shadows, one on your subject, one in the highlights — and read each one independently. On a high-contrast scene this is the whole game: meter the dark and the bright, not just an averaged guess.
• The Zone System, on your phone. Every pin is placed on a zone ruler from 0 (pure black) to X (pure white), with Zone V as middle grey. See the contrast range at a glance (“5 stops · III–VIII”) and a clear flag when the highlights or shadows will clip. Then place a reading in a zone: pick a pin, choose the zone you want that tone to sit in, and the exposure shifts so it lands there — and you can see whether the rest of the scene still fits or blows out. It’s Ansel Adams’ method, worked out for you in the field.
• Histogram and colour temperature, always on. A live luminance histogram (with clipping markers at the ends) and an estimated colour-temperature reading in kelvin sit on screen the whole time you’re metering — glanceable, no tapping required. When a scene is a strong colour rather than a shade of white — a deep blue-hour sky filling the whole frame, foliage packed edge to edge — there is genuinely no colour temperature to describe it, so rather than invent a number the reading shows a dash. The same goes for light at the far ends of the scale, like a frame lit by nothing but candle flame. Everyday metering is unaffected: skin, snow, shade, overcast, tungsten and sunset all read normally.
• Zoom to the framing you’ll actually shoot. Pinch to zoom continuously, or tap the preview to reveal a lens chip for each framing your phone actually has — 0.5× / 1× / 2× on a multi-lens phone. Metering follows the framing. On a phone with a single rear camera you get neither the chips nor the pinch: the meter never offers a framing the hardware can’t produce.
• Camera profiles. Tell the meter which body you’re shooting and it remembers that camera’s calibration, so readings line up with the gear in your bag.
• Reciprocity for film. Shooting film on a long exposure? Choose your film stock and, once the exposure is long enough for reciprocity failure to matter (past about a second), the meter shows the corrected shutter time and how many stops it added. On digital, it stays quiet — there’s no reciprocity failure to correct.
• Freeze the frame and experiment. Tap Freeze to grab a still, then drag the settings and watch how the exposure would change — the meter shows how many stops brighter or darker you’ve gone against the frozen reading, and the frozen image dims or brightens to match. Tap Live to go back to metering. It’s a risk-free way to play “what if I opened up two stops?” without chasing the light.
• Save a reading. Keep a reading for when you come back to shoot. Save it as a new spot where you’re standing, or add it to an existing spot — the frozen frame, the exposure settings and your GPS location are stored together, so next time you’re here you have the frame and the numbers you worked out, not just a pin on a map.
• Built-in help. Tap the ⓘ any time for a walkthrough of the controls.

Calibrate it to your gear (optional)

Because the phone is a reference meter, the absolute EV can sit a little off from a calibrated meter or your specific camera. If that bothers you, calibrate it once: open the settings from the ⓘ, set an EV offset so the EV the meter reports matches your camera or handheld meter, and the meter saves that offset to your camera profile and reuses it from then on. You never have to touch it again — and out of the box, with no calibration at all, the meter is already consistent enough to compare scenes and choose a starting exposure with confidence.

To be exact about what the offset moves: it shifts the EV figure the meter reports. The suggested aperture, shutter and ISO are worked out from what your camera metered, and the offset does not currently shift those — so treat it as reconciling the number you read, not as re-dialling the exposure for you.

The Light Meter on Android

Nothing here is available to install yet — Viewpoint for Android has not shipped.

Viewpoint for Android is on its way, and a Light Meter will come with it. Most of what’s on this page will be there — but not all of it, and we’d rather set out which is which than let you find out after you’ve paid.

Reading the light will work the same way. Point the phone at the scene and it will read the exposure value (EV) straight off the camera, updating as the light changes. Pick the side of the triangle you want to hold: in Aperture priority you set the aperture and the ISO and it will solve the shutter, and in Shutter priority you set the shutter and the ISO and it will solve the aperture. The figure the meter works out is the one it marks as automatic, so you will always see which of the three it is choosing for you.

Spot metering and the Zone System will be there. Press and hold anywhere on the live view to meter that tone, drop a few across the scene, and read each one on a zone ruler from 0 to X, with the contrast range and the same clipping flags. Placing a tone in a zone will work too: pick a pin, choose the zone you want that tone to sit in, and the exposure shifts to put it there — and before you commit, it will tell you what that would do to the rest of the frame.

The always-on readouts will be there. The live luminance histogram with its clipping markers, and the estimated colour temperature in kelvin — including the dash it shows instead of inventing a number for a scene that has no colour temperature at all.

Zoom will follow the framing. Pinch to zoom, or tap a lens chip. On a phone with only one rear camera you will get neither, rather than a chip for a lens it hasn’t got.

The rules behind all of that will be shared with the iPhone app — what a zone is, where a tone clips, when a scene has no colour temperature to report — so the two apps won’t disagree about what a reading means. The two phones read the scene through different cameras, though, so don’t expect the same number to the decimal on both. None of it will need a signal.

The settings you will be able to dial are a shorter ladder than the iPhone app’s: whole stops from f/2.8 to f/16, shutter speeds from 1/1000 to 1/30, and ISO 100 to 1600.

Camera profiles and calibration will be there. Tell the meter which body you’re shooting from the profile chip, and calibrate it once from the ⓘ: set an EV offset so the EV the meter reports agrees with your camera or your handheld meter, and it’s saved against that profile and reused from then on. Switch bodies and the offset saved for that body applies. With no calibration at all the meter works exactly as it does now — the offset starts at zero and nothing waits on it. As on iPhone, the offset shifts the EV figure rather than the suggested aperture, shutter and ISO.

Film reciprocity will be there. A second chip under the profile picks what’s loaded in that body — digital, or film with mild or strong reciprocity failure. Choose a film stock and, once the exposure the meter is suggesting is long enough for reciprocity failure to matter, a line appears with the corrected shutter time and how many stops it added. On digital there’s no such line at all: there is no reciprocity failure to correct, so the meter says nothing about it. The correction itself is the same one the iPhone app makes — it comes from the same shared engine — and it follows whatever you’ve dialled, including a tone you’ve placed in a zone. Your choice of stock is remembered, and it’s independent of the camera profile: switching bodies doesn’t change what’s in the camera.

Freezing the frame will be there. Tap Freeze and the meter holds the last frame as a still while the reading stays with it. Drag the settings and a badge tells you how many stops brighter or darker you’ve gone against what was metered, and the still washes a little lighter or darker to match — a cue, not a preview of the photograph. The histogram and the colour reading hold with the frame too, so everything on screen describes the same moment. Tap Live to go back to metering with nothing left over.

Saving a reading will be there. Tap Save reading and the held frame, the exposure you’ve settled on and your GPS position are kept together — as a new spot where you’re standing, or added to a spot you already have. It’s the same offline-first path the camera uses: written to your device straight away and queued to sync when you’re back in range, so you can keep a reading deep in the backcountry and lose nothing.

The built-in help will be there. Tap the ⓘ and the guide above opens inside the app — not a link out to a browser — alongside the calibration control, in your language where we have translated it and in English otherwise. It’s bundled with the app, so it works with no signal.

What will be different from the iPhone app: the shorter stop ladder above, and nothing else on this page. We’ll keep this section honest as that changes.

Works offline

The Light Meter runs entirely on your device — the metering, the priority math, the Zone System, reciprocity and the readouts all work with no signal. Saving a reading follows Viewpoint’s offline-first rule too: it’s written to your device immediately and syncs when you’re back in range, so you can meter and save deep in the backcountry and never lose a thing.

Related

• Photography basics — exposure, the exposure triangle and the Zone System explained.
• Calculators — depth of field, hyperfocal, long-exposure and more, for when you want to plan the numbers rather than meter them.