fiat lux - a lightmeter for film photography

fiat lux — let there be light

A roll of film has one speed for its whole length. Get the light wrong and there is no undo, only the next thirty-six frames.

fiat lux is a light meter for cameras that do not have one of their own. Point the phone, read the exposure, set the camera by hand.

What it does
- Meters through the phone's camera, the way a reflected meter does. Tap the viewfinder to meter a spot.
- Pairs every aperture with the shutter speeds your camera really has, on a dial. The nearest speed is chosen and the dial says how far off it is; tap another speed to go over or under on purpose.
- Knows your cameras: built-in or interchangeable lenses, shutter in the body or in the lens, and the speeds and apertures they actually have, odd ones like 1/300 included.
- Load a film and meter at its speed, pushed or pulled. Over fifty current films are listed, with favourites.
- Log shot takes a photo with the settings burnt in and counts the frame. Each roll has its own page, and History shows how much you shoot, by day, camera and film.
- Quick Meter for everything else, at any ISO.
- Calibrate against a meter you trust.

Where it works
Tested on the Jolla Phone (2026) only, where the camera reads 4 stops low out of the box; Calibrate starts at +4 to correct that. Lux reaches the camera through Android's Camera2 via libhybris, so it needs a phone whose Android side offers Camera2. On any other phone, check it against a meter you trust before you trust it with film. Nothing else needs to be installed.

Your data
Cameras, lenses, films, rolls and frames are kept in one database on this phone. The camera is used only to meter and to take the picture when you log a shot; those pictures are saved in Pictures/FiatLux. No account, no network access, nothing reported anywhere.

The name
fiat — Latin, let there be. From fiat lux in the Vulgate: let there be light, and there was light. The first app took the phrase. The rest of the family kept the verb.
lux — Latin, light. The word the whole family took its name from, given back to the one app that measures it.

Fiat lux. Et facta est lux.
Let there be light. And there was light. — Genesis 1:3, Vulgate

Built on RAWfish by Logic-gate (BSD 3-Clause): Lux carries its own copy of RAWfish's Camera2 helper and bridge.

Part of the fiat family — small, focused Sailfish OS apps that do one thing plainly.
Source on GitHub · MIT licence: https://github.com/munksh/FiatLux

Only 64-bit atm, since it's only tested and tried on the Jolla Phone 2026, I'd really have no idea to make this work on another phone, sorry </3