Open-source light meter

Calegari Meter

A pocket light meter you print at home. An AMOLED face, a translucent dome on top, a knurled dial and a red key. Reflected and incident light, flash, colour temperature and the zone system.

Build guide Download everything

Why

A meter for a view camera.

The Calegari View 2 wants a meter that is quick, quiet and exact, and that speaks the language of a lens in a Copal shutter: whole stops of time, thirds of aperture, long exposures on slow film, a flash now and then.

The meters that do all of that are big or expensive. This one is a small black block that sits in the hand like a first iPod shuffle, with the manners of a Leica: one red dot, one red key, a dial you turn without looking. Its shape comes from the object, not from the board inside it.

Seven printed parts, three bought boards, a battery and seven wires. No screws, no glue.

Specifications

Small, and complete.

Size

41.6 × 55.7 × 21.4 mm

plus the dial and the dome on top

Screen

1.8″ AMOLED

368 × 448, touch; black, warm white and one red

Light

Reflected and incident

a 44° cone through the port; the dome for incident, recognised by itself

Answer

Aperture or shutter priority

whole stops or thirds of time, ISO 6 to 6400, compensation in thirds

Film

Reciprocity

HP5, FP4, Delta 100 and 400, Pan F, Tri-X, Acros II

Flash

Cordless

the aperture in tenths, and the share of flash and ambient

Colour

Kelvin, tint, filter

eight spectral channels; the Wratten filter; flicker at 100 or 120 Hz

Zone

III to VIII

shadows and highlights: the range, N±, the exposure

Bought

About 60 EUR

Waveshare AMOLED board, Adafruit AS7341, an encoder, a LiPo cell

Gallery

Every angle.

Front: the glass stands 0.6 mm proud; the band above it is the top plate

Side — Right side: the red key, the power key, USB-C

Top: the dome over the sensor, the knurled dial

Rear — Back: a plain lid, the shadow line all round

Dome parked — Reflected light: the dome parks under the foot

Inside: the battery behind the screen, sensor and dial across the top

Screens

The answer, large.

The biggest thing on the screen is always the answer, set like the numbers on a shutter dial. The value the dial changes has a red line under it. At the foot a scale slides to the answer like a real dial. Every screen here is drawn by the firmware's own code.

Long exposure — 29 s on HP5, reciprocity corrected

Colour: 3180 K, an 80A for daylight film

Colour, fluorescent — Green tint and flicker under a tube

Settings: the dial changes, the red key chooses

How it works

Two shells, three boards.

The screen boardWaveshare's ESP32-S3 with the AMOLED, charger, power key, speaker and USB-C on one board behind the glass. It is the face.
The sensorAn AS7341 with eleven channels lies across the top under a port. The port's rim is the stop for reflected light.
The domeA solid half sphere of translucent PETG, pressed into a seat over the port. The sensor's own LED, under its flange, tells the meter it is there.
The dialAn EC11 encoder threaded into the top wall, a knurled dial on its shaft.
The keysA red key and a black pill snap through the side wall onto the board's own buttons.
The trayIt stands on the board where it has no parts; two printed leaf springs take the lid's posts, so the lid holds the glass against the window with a light, even push.

Build

Seven wires, one hour.

Three plates, no supports: every curve lies in the plane of the bed, every rising edge is vertical or a 45° chamfer. Solder seven wires, drop the screen in, snap the lid on, load the firmware with one command.

Step 1

Seven wires

Four to the sensor, three to the encoder, all to one header on the back of the screen board.

Step 3

The screen

Face first into the window, onto the ribs, its buttons behind the two keys.

Step 4

Sensor and dial

The sensor into its groove under the port, the encoder threaded into the top.

Steps 5 and 6

Tray, battery, lid

The tray on the board, the cell on the tray, four snaps: the lid's posts press the tray's springs and hold the screen.

Checked before it is printed

Measured, not guessed.

interferences between any two parts, bought or printed

supports needed, on any of the three plates

22°

half angle of reflected light, set by the rim of the port

screens, rendered on a computer by the firmware's own code

The first meter has not been put together yet. Two numbers in the firmware come from the datasheets and are confirmed with the first build: the calibration guide says how.

Files

Everything you need.

Print platesThree 3MF plates for a 180 mm bed: black, red and translucent white, parts already oriented.print/plates → Shopping listScreen board, sensor, encoder, battery, wire.docs/bom.md → Printing guideMaterials, orientations, layer heights, painting the dots.docs/printing.md → AssemblySeven wires and six illustrated steps.docs/assembly.md → FirmwarePlatformIO: one command over USB. The screens also run on a computer.docs/firmware.md → CalibrationThe dome, the light against a meter you trust, the colour against a halogen bulb.docs/calibration.md → Using the meterThe controls, the four modes, every setting.docs/using.md → Design notesSeven rules for the form, and why they are also rules for printing.docs/design.md → Parametric modelPython and build123d, with STEP files of every part in print/step.cad →