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Light Meter

Measure light with your phone camera and shoot perfectly exposed film.

Metering

Nothing the camera sees leaves your phone. Tap the image to meter a spot.

— · — Turn on the camera or meter with a photo

Your film and your camera

Film ISOthe one on the box

Prioritythe value you set

Fixed apertureit works out the other one

Stopshow your camera clicks

Compensation+ brighter · − darker

Equivalent exposuressame exposure

They all give the same exposure. Pick what you need: a fast shutter to freeze motion, a wide aperture (small number) to blur the background.

Calibratenot calibrated

Every phone is different. Calibrate once and it stays saved on this phone. Meter first, then choose how to calibrate.

Clear day, full sun behind you: meter (average) something ordinary lit by the sun, like grass, a wall or the street, and tap the button.

Match another light meter, or a camera with a meter, metering the same thing:

Aperture

Shutter

ISO

Roll notebook0 shots

Write down the settings of every shot. When you get your film developed, compare and learn. It stays saved on this phone.

Film

Camera

⚠ Before you trust the reading

It's a helper, not a certified instrument. Accuracy depends on your phone. For color negative and black and white film (which forgive 1 or 2 stops of error) it's more than enough; for slide film or shots you can't repeat, bracket (one brighter, one darker) or use a handheld meter.
Live vs. photo. On some Android phones the browser can control the camera exposure and the meter works live. On iPhone and many other phones that isn't allowed: there the accurate reading is “Meter with photo”, which reads the exposure data stored in the photo. If your phone doesn't store it, you'll be told.
It measures reflected light, like the meter in any camera, and assumes the scene is middle gray. Snow, beaches and white backgrounds fool it (you get dark photos: compensate +1 or +2), and so do black backgrounds or stages (you get bright photos: compensate −1 or −2). For what matters, spot meter a midtone, like grass or tanned skin.
Phones process their photos (HDR, “smart” photos), and that can shift the reading, especially against the light. That's why it's worth calibrating once.
Exposures longer than 1 second: film loses sensitivity (reciprocity failure). Add time according to your film's datasheet; the meter doesn't correct for it.
Values are rounded to your camera's nearest stop. Old shutters are often inaccurate, especially at slow speeds.
Your phone sees wider than most lenses. If you use a telephoto, spot meter what matters to you.
Your privacy: the camera image and metering photos are analyzed on your phone and are never saved or sent anywhere.

Free online light meter for film cameras

This light meter uses your phone camera to measure light and tells you which aperture and shutter speed to set on your film camera for your film's ISO. It runs in the browser with nothing to install, though you can also install it as an app.

How to use it

Pick your film's ISO and the value you want to set: aperture or shutter speed.
Turn on the camera and point it at what you're shooting, or tap “Meter with photo”.
To meter a spot, tap that part of the image (for example, a backlit face).
Set the aperture and shutter speed shown in large type on your camera.

Sunny 16 rule (no meter)

Light	Aperture	ISO 100	ISO 200	ISO 400
Snow or sand in sun	f/22	1/125	1/250	1/500
Full sun, hard shadows	f/16	1/125	1/250	1/500
Weak sun, soft shadows	f/11	1/125	1/250	1/500
Overcast, no shadows	f/8	1/125	1/250	1/500
Heavy overcast or open shade	f/5.6	1/125	1/250	1/500
Sunset	f/4	1/125	1/250	1/500

FAQ

Can a phone work as a light meter for a film camera?

Yes, in most situations. A phone camera measures reflected light just like the meter in a camera. For color negative and black and white film, which tolerate one or two stops of error, it is more than enough. For slide film, bracket your shots or use a handheld meter.

Why do I have to meter with a photo on iPhone?

Safari does not give web pages the live exposure data of the camera. A photo, however, stores its shutter speed, aperture and ISO, and with that the light meter works out the real light level.

What is EV?

Exposure value: a single number for how much light there is. Each EV step is double or half the light. A sunny day is around EV 15 (at ISO 100), an office around EV 8 and a street at night around EV 4.

What is the Sunny 16 rule?

In full sun, at f/16, the right shutter speed is roughly 1/ISO of your film: with ISO 100, f/16 at 1/125. It is handy to calibrate the meter and as a backup when you have nothing to meter with.

When should I use compensation?

When the scene is much brighter or darker than middle gray: snow, a beach or a white background (+1 or +2), or a stage or black background (−1 or −2). Also when you want a brighter or darker photo on purpose.

Are my photos uploaded anywhere?

No. Everything happens on your phone: the camera image and the metering photos are analyzed in the browser and never sent to any server.

DecimuLabs · La Plata, Argentina