Support
Quick answers first. If yours is not here, write to us — a person reads every message.
Where do the formulas and the film data come from?
The hole follows d = c·√(f·λ), with one of four published constants: Petzval’s √2 ≈ 1.414 (1857), Young’s √2.44 ≈ 1.562 (Applied Optics, 1971), Rayleigh’s 1.9, his visual optimum (Philosophical Magazine, 1891), and Rayleigh’s theoretical 2 (Nature, 1891). The reciprocity corrections are the film makers’ own, read from their datasheets, and each film links to the datasheet it came from.
Why do some films say “no published data”?
Because the maker publishes nothing past one second, or only says to make tests. The app never guesses: a guessed correction costs a frame.
Why do some films show the maker’s words instead of a time?
Some makers give the correction in stops of aperture. A pinhole cannot open its aperture, and adding time instead is not what the maker said, so the app shows the maker’s words and works nothing out.
Why is there no answer past the end of a maker’s table?
A maker’s table stops at the longest time it tested. Past that, any number would be an extrapolation, so the app says the time is beyond the table.
The light meter shows a different value from my meter.
Phone meters vary. Use the calibration setting in Expose, and check it once against a meter you trust.
How do I measure a hole?
Scan the hole on a flat scanner, or photograph it next to a ruler, and choose the picture in the app’s Measure screen. The picture is read on the phone through the system photo picker and is not kept.
How do I report a mistake?
Open the film on 35mm.org and use “Suggest a time or report a mistake” at the foot of its page, with the source if you have one. A curator checks it against the source, and nothing you send is shown on the site by itself.
Which devices and languages does it support?
iPhone and iPad with iOS 17 or later. The app is in 13 languages.
Do I need an account?
No. There is no account, no sign-in, no analytics and no advertising.
How do I delete my data?
It is on your phone: your saved cameras and your exposure log are files there. Delete a profile or the log in the app, or delete the app, and it is gone. We hold no copy.
Contact
Write to us
A support address will be published here.
Found a mistake in a time?
Open the film on 35mm.org and send a correction with its source — it goes straight to the people who keep the reference.