SlowLightMeter vs ProFilm Meter

As a film photographer, I wanted an accurate yet simple reflective and incident light meter. After trying several, I decided to build my own. This light meter continuously measures light, so it requires minimal interaction during a shoot. To avoid accidentally changing film ISO, I added an ISO lock. And since I shoot often with my Hasselblad, I made EV values a core feature of the app.

ProFilm Meter is the most complete light meter and exposure toolkit for film photographers. From 35mm to 8×10 large format, dry plates to tintypes, it handles every calculation you'd normally reach for three separate tools to solve — all offline, all in real time. LIGHT METERING Your phone's camera becomes a precision reflected-light meter. Choose spot, center-weighted, or average metering and dial in exposure with ⅓-stop, full-stop, or any combination of increment sets running simultaneously. A live RGB histogram keeps highlight and shadow zones in view at all times. Native per-frame ISO, shutter, and aperture capture at ~10 fps Multi-point metering: average 2–4 scene readings into one exposure value Tap-to-focus and multi-lens camera selection Adaptive EV smoothing adjusts for scene changes automatically Screen stays awake during active metering sessions CALIBRATION Two-point guided calibration locks each camera to a trusted reference. After calibration, a fine-tune step lets you match any external meter in ⅓-stop increments. Uncalibrated cameras are gated with a full-screen prompt so you never shoot on an unmeasured body. FILM STOCKS & RECIPROCITY An on-device film stock library covers 35mm, 120, and large format emulsions — including the full Zebra Dry Plate collection. Every stock carries its own reciprocity profile. Eight built-in profiles (Acros II, T-Max, HP5+, Portra, Fomapan, Zebra, and more) plus full custom profile creation, including Schwarzschild p-factor and optional threshold. Add custom film formats and reciprocity profiles inline, without leaving the film stock screen. COMPENSATIONS Reciprocity failure — corrected automatically for exposures beyond threshold Bellows compensation — calculated stop-for-stop from draw and focal length RA4 Color Reversal — estimates scene color temperature and gives you Mired-shift filter corrections for color positives; works in both ambient and flash mode Spectral sensitivity — metering coefficients adjusted for panchromatic, orthochromatic, and blue-sensitive emulsions Lens filters — ND (1–10 stops), polarizer, yellow/orange/red/green contrast filters, R72 and deep IR, plus custom filters Positive/reversal process — +0.5 stop compensation, auto-enabled for tintype stocks UV/environmental compensation — adjustable for altitude and atmospheric conditions IR Light Estimator — dedicated tool for infrared exposure estimation FLASH Flash metering detects incident flash via fast polling with peak-hold and sticky arming. A built-in flash trigger supports Optical Slave (fires the LED torch to trip slaved units) and Cable Sync (audio click for USB-C to PC-sync adapters). VIEWFINDER A lens-independent viewfinder zoom gives consistent framing regardless of which physical lens the phone uses. Overlay your chosen film format frame lines and compose like you're looking through a director's viewfinder. FIELD JOURNAL Save any exposure to the journal with one tap. Each entry records ISO, aperture, shutter speed, EV, reciprocity correction, RA4 and spectral corrections, GPS coordinates, and a cropped preview photo. Entries are exportable and shareable. EXTRA TOOLS Depth of Field Calculator — for any format and focal length Zebra Exposure Guide — zone-system reference for dry plate work Alternative Processes Meter — cyanotype, platinum, salt print, and more Step Wedge Tool — exposure planning for contact printing Rolling Shutter Calculator — flash sync safety for focal-plane shutters 20 FILM FORMATS 35mm · 6×4.5 · 6×6 · 6×7 · 6×9 · 4×5 · 5×7 · 8×10 · 9×12cm · 10×10 · 10×12 · 11×14 · 12×12 · 13×18cm · 20×24 · Sixth Plate · Quarter Plate · Half Plate · Whole Plate · custom dimensions 7 LANGUAGES English · Slovenian · Spanish · French · German · Japanese · Simplified Chinese PRIVACY All metering and calculation runs entirely on-device. No account required. No data leaves your phone.