Long exposure · iOSTimerGlass
A field companion for long exposures on film.
Reciprocity correction, filter and bellows compensation, pinhole geometry, exposure estimation and long-exposure timing — gathered into one quiet, considered tool beside the camera.
By the studio · iOS
What it is
In film photography, reciprocity says that density depends on total exposure (light intensity × time). But once the exposure grows long — usually beyond a second — the rule breaks down: this is reciprocity failure, the Schwarzschild effect. The film becomes ‘slower’, the meter's time is often not enough, and the correction curves differ from stock to stock and maker to maker. Leafing through PDFs and data sheets in the field is slow and error-prone.
TimerGlass is made for exactly this: it gathers reciprocity correction, filter and bellows compensation, pinhole geometry, exposure estimation and long-exposure timing into one quiet, retro-flavoured tool — so whether you are shooting large format landscapes at dusk, a pinhole long exposure, or 135 / medium format at night, you get a trustworthy result quickly, right beside the camera.
The problem it solves
- Metered time ≠ the time you should actually expose: long exposures need reciprocity correction by film stock, or you risk underexposure.
- Filters and bellows add time: ND, GND, CPL, colour filters and centre ND, plus bellows extension in large format close-ups, all change the final time and must be counted in.
- A pinhole has no aperture stops: you first work out the pinhole and effective aperture, then estimate exposure, then time it.
- A long exposure isn't just ‘how long’: you also have to remember to close the shutter, see the progress after the screen locks, and reckon with contrast and colour shifts at the development and scanning stage.
TimerGlass links these steps into one field workflow.
Core capabilities
Reciprocity-failure calculation (the core)
Enter your metered time and see the corrected exposure instantly, with the reciprocity curve for that stock so you understand how metered time maps to real time.
- 100+ common film stocks: black and white, colour negative, colour reversal, plus some experimental and paper stocks
- Brands including Ilford, Kodak, Fujifilm, Foma, Rollei, ADOX, CineStill, Lomography, Harman, Kentmere and Bergger
- Curves based on manufacturer data — power-law formulas or table interpolation, according to each stock's real behaviour
- Favourite your regular stocks and filter by brand or type for faster switching on location
Filter and bellows compensation (worked out in one pass)
Filter stops and the bellows factor are folded into the same reciprocity calculation, so the output is the final time to open the shutter.
- Filter library: ND (ND2–ND32000), graduated GND, polarising CPL, black-and-white contrast colour filters (yellow / orange / red / green / blue) and the centre ND common in large format (e.g. Schneider specs)
- Stack filters, or add a custom filter — including a variable ND entered by measured stops
- Bellows extension: enter focal length and extension, and light loss is compensated automatically by (extension / focal length)²
Pinhole tools
Everything a pinhole exposure needs, before there is any aperture to read.
- The optimal pinhole diameter for a focal length (Lord Rayleigh), and the resulting effective aperture
- Against your actual pinhole, a cue for too small (diffraction) / near optimal / too large (geometric blur)
- Equivalent angle of view by format, to picture the coverage
- Built-in Sunny-16 scene presets (sunny snow, sunny, hazy, cloudy, heavy overcast, shade, indoor window light, night lighting and more) that flow straight into the reciprocity calculation and timer
A long-exposure timer
A countdown built for long exposures, so exposure and timing stay aligned.
- Start it in sync with opening the shutter
- Live Activity and Dynamic Island: the remaining time stays accurate on the lock screen and with the screen off
- A reminder to close the shutter at the end, so you don't ‘forget the curtain’ — notifications tuned for long-exposure use
- Send a finished calculation straight to the timer, with less switching back and forth
Practical long-exposure guidance
Reciprocity correction answers ‘how long’; a long exposure also brings effects at the development and scanning stage. TimerGlass gives situational notes by actual exposure time and stock type:
- Black and white: contrast may rise — a hint to pull-process a little
- Colour negative: long exposures may shift toward cyan — pointers on filters and scanning
- Reversal (E-6): hard to rescue by pulling, so more emphasis on colour temperature and filters while shooting
Exposure history and sharing
Look back at what worked, and share it.
- Recent exposure settings — stock, metered time, corrected time, filters, bellows — recorded automatically for review and comparison
- A refined share card to pass a setup to a friend or keep as a note
Custom film stocks
For a stock the database doesn't have, add your own — good for handmade stocks, discontinued films, or correction data you've measured yourself.
- Define the curve with a power law, or
- Enter manufacturer data points as a lookup table
Works with MeterGlass
TimerGlass pairs with its sibling metering app, MeterGlass. MeterGlass offers averaging metering, roughly 1.5° spot metering, multi-point Zone System metering and format masking from 135 to 8×10; the shutter time it measures can be sent to TimerGlass in a tap, flowing straight into the reciprocity calculation. Meter, correct, time — one field chain.
Design and experience
- Made for the field — one hand on the camera back, the other on the phone: a clear hierarchy, with the key result visible at a glance
- A retro, film-flavoured interface, with light / dark / follow-system
- Six languages: Simplified Chinese, Traditional Chinese, English, Japanese, German and French
- Privacy: no data collection; calculations and history stay on your device
Who it's for
- Large format and pinhole photographers who shoot long exposures often
- 135 / medium format film users chasing dusk, blue hour, night scenes, flowing water and cloud
- Serious film enthusiasts who want ND, bellows and reciprocity worked out in one pass
- Anyone tired of reading data tables by torchlight in the field, who wants a quiet, dependable tool
TimerGlass — a reciprocity calculator, filter and bellows compensation, pinhole and exposure estimation, and a lock-screen-ready long-exposure timer: a one-stop companion made for long exposures on film.
Download on the App Store