PROFILM METER
Turn Your Phone into a Precision Light Meter for both Film & Plate Photography
ProFilm Meter turns your phone into a highly accurate light meter engineered for demanding analog workflows. Designed for both modern film and historical processes, it delivers precise exposure readings across materials with different spectral sensitivity modes including blue-sensitive, orthochromatic, and panchromatic. Advanced features such as two-point calibration, reciprocity failure correction, bellows compensation, and real-time colour temperature analysis ensure reliable results in any lighting condition.
Available on Android and IOS
The professional light meter built for film photographers. On your phone.
Precise. Trustworthy. Film-first.
Most light meter apps are built for digital photographers who think in stops and histograms. ProFilm Meter was built from the ground up for the way film photographers actually work — with reciprocity failure, spectral sensitivity, bellows compensation, and the ritual of getting the exposure right before you press the shutter.
Whether you're shooting 35mm on the street or a 4×5 sheet in the studio, ProFilm Meter gives you the accuracy and depth of a dedicated meter in the device you already carry.
Real metering. Real control.
Four metering modes. Spot, center-weighted, average, and multi-point — take up to four readings and let the meter calculate the averaged EV automatically. Bracket without guessing.
Three priority modes. Aperture priority, shutter priority, or full manual. Lock your exposure and work the scene.
Flash metering. Trigger via optical flash sync, cable, or ambient light sensor. The meter captures peak luma, calculates your flash EV, and even suggests RA4 filter packs from the flash's color temperature. No separate flash meter required.
Live color temperature. See the scene's CCT in real time, so you know what you're printing into before you shoot.
Built around your film.
ProFilm Meter ships with a library of the most-used emulsions, and connects to a continuously updated remote database of film profiles you can pull in on demand. If your stock isn't there, add it yourself — with custom ISO (including fractional values), spectral sensitivity, and its own reciprocity curve.
Spectral sensitivity modes let you shift the meter's response to match how your film actually sees light: Panchromatic, Orthochromatic, Blue-sensitive, and Infrared.
Reciprocity is handled automatically. Every film profile carries its own Schwarzschild p-factor. Long exposures are corrected in real time so the time you set is the time that works.
Every tool you actually need.
Reciprocity Calculator — Corrects metered time to compensated time for any film in your library. Adjustable threshold per stock.
Depth of Field Calculator — Near and far focus limits, hyperfocal distance. Pick your format, focal length, and aperture.
Bellows Compensation — Enter focal length and extension distance, get the exact number of stops to add. Macro and large format ready.
IR Estimator — Estimates infrared offset for 720nm and 850nm filters from the current scene EV. No more bracketing blind.
Rolling Shutter Calculator — Know whether your shutter speed will cause banding artifacts before you fire.
Step Wedge Tool — For darkroom workers calibrating film development and printing processes.
Zebra Exposure Guide — Visual zone mapping that puts skin tones, shadows, and highlights into context for your scene.
Alternative Processes Meter — Exposure guidance for cyanotype, platinum-palladium, silver gelatin, and other non-standard processes.
RA4 Color Engine — CMY filter pack recommendations direct from the scene's color temperature. Walk into the darkroom with a starting point, not a guess.
Calibrated to your device. Your lens. Your workflow.
No two phone cameras are the same. ProFilm Meter includes a full two-point calibration system — calibrate to a dark reference and a bright reference to correct your specific sensor. Front and rear cameras are calibrated independently. Lens calibration accounts for field-of-view differences between your phone's optics and the lens on your camera.
The result is a meter you can actually trust.
Shoot and record.
Every exposure gets saved to your journal — ISO, aperture, shutter speed, EV, focal length, film stock, GPS location, date, and a cropped snapshot from the viewfinder at the moment you metered.
Share individual entries as a branded ProFilm Card — a photo with all your exposure data overlaid, ready to post or archive. Or export a full digital contact sheet across multiple entries.
Your gear. Your way.
Build out your kit in the app: custom lenses, custom aperture series (full, half, third, or two-third stops), and custom film formats down to the millimeter. Save your favorite camera, lens, and film combinations as Preferred Setups and switch between them in a single tap.
Environmental compensation runs automatically in the background — elevation and UV index adjust your readings based on GPS and local weather, so you're always metering for the conditions you're actually shooting in.
Available in eight languages.
English · Español · Français · Deutsch · Slovenčina · 日本語 · 中文
Metric and imperial. Your choice.
Instructions to build your own Camera to flash sync cable
Warning, if you mess this up you may destroy your phone. If you do it is on you
Parts Required
Qty Part Notes
1 PC817C opto-isolator 4-pin DIP IC
1 2N3904 NPN transistor TO-92 package
1 47Ω resistor Yellow – Violet – Black
1 100Ω resistor Brown – Black – Brown
1 TRRS 3.5mm plug 4-conductor (not TRS)
1 PC sync socket/cable Co-axial / Prontor-Compur
Identifying Your Components
PC817C Opto-isolator (4-pin DIP)
The IC is a small black rectangle with 2 legs on each side. One corner has a small dot or notch moulded into the plastic — that is Pin 1.
Hold it with the dot at the top-left, legs pointing down:
dot
·
┌────┴────┐
1 │ Anode │ 4 ← Phototransistor Collector (output to flash)
│ (+) │
2 │ Cathode │ 3 ← Phototransistor Emitter (output to flash)
│ (−) │
└─────────┘
INPUT side OUTPUT side
(from phone) (to PC sync)
Pins are numbered anti-clockwise from the dot.
Diode direction: Current must flow in at Pin 1 (Anode, +) and out at Pin 2 (Cathode, −). Wired backwards = nothing triggers, no damage, just silence.
2N3904 Transistor (TO-92)
Small black D-shaped component with 3 legs. Hold it with the flat face towards you, legs pointing down:
___
/ \ ← flat face toward you
| |
|___|
| | |
E B C
Left = Emitter (E)
Middle = Base (B) ← signal in
Right = Collector (C) ← connects to PC817C
3.5mm TRRS Plug (CTIA — iPhone / most modern Android)
Conductors from tip to base:
──── Tip (1st) = Left audio — not used
──── Ring 1 (2nd) = Right audio — not used
──── Ring 2 (3rd) = Mic Bias ← ~1.8–2.2V DC ← USE THIS
──── Sleeve (4th) = Ground (GND)
OMTP phones (older Samsung/some Android): Ring 2 and Sleeve are swapped. Check your phone spec before soldering — shorting Mic Bias to GND can damage the phone.
Full Circuit Diagram
PHONE 3.5mm TRRS (CTIA)
─────────────────────────────────────────────────────
Ring-2 (Mic Bias ~2V)
│
[47Ω] ← base resistor
│
└──────► 2N3904 Base (B = middle leg)
Sleeve (GND) ──────────────────► 2N3904 Emitter (E = left leg)
2N3904 Collector (C = right leg)
│
[100Ω] ← LED current limiter
│
PC817C Pin 1 Anode (+) ← dot corner
PC817C Pin 2 Cathode (−) ──── GND (same as Sleeve)
PC817C Pin 4 Collector ──────► PC Sync (+) centre/tip
PC817C Pin 3 Emitter ──────► PC Sync (−) outer/sleeve
─────────────────────────────────────────────────────
Step-by-Step Build
Step 1 — Base resistor
Connect 3.5mm Ring-2 → one end of the 47Ω resistor → other end to 2N3904 Base (middle leg).
Step 2 — Emitter to ground
Connect 2N3904 Emitter (left leg) → 3.5mm Sleeve (GND).
Step 3 — Collector to opto-isolator
Connect 2N3904 Collector (right leg) → one end of the 100Ω resistor → other end to PC817C Pin 1 (Anode, dot corner).
Step 4 — Cathode to ground
Connect PC817C Pin 2 (Cathode, bottom-left) → GND (same wire as Sleeve).
Step 5 — Output to flash
Connect PC817C Pin 4 (Collector, top-right) → PC sync centre/tip (+).
Connect PC817C Pin 3 (Emitter, bottom-right) → PC sync outer/sleeve (−).
Common Build Mistakes
PC817C wired backwards — If you have Pin 1 and Pin 2 swapped (dot corner going to GND instead of toward the transistor), the internal LED is reverse-biased and will never light. Nothing triggers. Check the dot corner orientation.
Transistor inserted backwards — If the curved face is toward you instead of the flat face, Emitter and Collector are swapped and the transistor won't switch. Flat face = E / B / C from left to right.
Using Tip instead of Ring-2 — The Tip carries AC audio, not the DC bias you need. You must use a 4-conductor TRRS plug and connect to Ring-2 (the third conductor from the tip).
Resistors swapped — 47Ω goes between Ring-2 and the transistor Base. 100Ω goes between the transistor Collector and PC817C Pin 1. Swapping them over-drives the base or under-drives the LED.