Luma · Light Meter

One screen, three values: the aperture, shutter speed and ISO to dial in on your camera. Live metering, a haptic dial, and an honest "out of range" when it is.

A mechanical camera does not forgive an exposure mistake: on a roll of 36, you only see your misses at the lab. Luma answers the one question that matters as you raise the camera — which aperture, which shutter speed, for this scene and this film?

No shot log, no frame counter, no hidden settings. One screen, three values.

LIVE METERING Your iPhone's camera becomes the meter. Luma continuously reads the exposure the phone settles on and converts it into an ISO 100 normalised EV, smoothed for a stable reading. No photo is ever saved: the image is analysed, then forgotten.

ONE RECOMMENDATION, NOT A LIST Luma shows a single aperture and shutter pair, chosen for handheld shooting: at least 1/125 s to stay clear of camera shake, then f/5.6 to f/8 where the lens is sharpest. When light runs short, it opens the aperture before slowing the shutter.

THE DIAL Every equivalent aperture / shutter pair scrolls under your thumb with clicking haptic feedback, like the shutter dial on the body. Pick f/2.8 to lift a portrait off its background, f/16 for a landscape sharp front to back — the shutter speed follows.

SPOT METERING Tap the viewfinder to place the metering circle on your subject: a backlit face, a shadow worth keeping. Tap the circle to return to average metering.

IT REFUSES TO LIE When the scene falls outside the camera's range, Luma says so — too dark, too bright — and shows no values at all. A wrong recommendation would be worse than none.

IT EXPLAINS Two lines under the values: what the shown aperture does to depth of field, what the shown shutter speed means for shake. Enough to learn, roll after roll.

FILM STOCKS Portra 160/400/800, Ektar 100, Gold 200, UltraMax 400, HP5+ 400, Tri-X 400, Delta 100/400, Fomapan 100/400 — plus manual ISO entry for everything else, including pushed or pulled film. Your choice stays loaded for the whole roll.

BUILT FOR A SPECIFIC CAMERA Luma is calibrated for a Nikon FM2 with a 28 mm f/2.8 lens: 1 s to 1/4000 s, f/2.8 to f/22. It serves any manual camera sharing that range just as well — simply transfer the values to the stops your gear actually has. Independent project, not affiliated with Nikon; trademarks are named only to describe compatibility.

IT ASKS FOR NOTHING No account, no ads, no network access: Luma works fully offline and collects no data whatsoever. Free, no in-app purchases, open source.

Please note: the app's interface is in French.

Luma is an aid, not a guarantee — cross-check it against a reference meter on a few scenes before trusting it with a roll.