Film development calculators on iPhone: temperature, push, dilution, reciprocity
Last updated 2 June 2026
EditMe bundles five darkroom calculators that run on your iPhone with no chemistry chart and no connection. It compensates development time for a temperature that differs from your reference, adjusts time for pushing or pulling with separate factors for black and white and C-41, mixes a dilution from a total volume and a ratio you type as 1+9 or 1:9, corrects long exposures for reciprocity failure per film, and lays out a print test strip in even f-stop steps. Everything computes on the device, so you can run the numbers at the enlarger or over the tank without looking anything up.
What the five calculators actually do
Each tool is a small, focused panel. You set a couple of values and the corrected number appears straight away.
- Temperature compensation. Enter your reference time and temperature and the temperature you are actually developing at. It shortens or lengthens the time as developer activity rises or falls with heat, using an Ilford-style time-temperature approximation.
- Push and pull. Pick the process, set a base time, and dial stops from minus three to plus three. Black and white and C-41 use different per-stop factors, because C-41 responds more weakly to a longer first developer.
- Dilution mixer. Give a total volume and a ratio. It parses 1+9, 1:9, or Stock and splits the result into millilitres of concentrate and water.
- Reciprocity. Choose a film and enter the metered seconds. Above one second it raises the time to that film's reciprocity exponent, so a four second reading becomes the longer corrected exposure.
- Print test strip. Set a base time and a strip count, and it generates bands in even f-stop steps, showing the extra seconds to add per band and the running total.
Why offline, on-device math matters in a darkroom
A darkroom is a bad place for a browser. Your hands are wet, the light is dim or red, and a chemistry chart on a wall does not adjust for the temperature you actually measured. These calculators are plain, deterministic functions that live in the app, so they give the same answer every time and need no signal.
- No connection, no account. The math runs on your iPhone. There is nothing to sign in to and nothing to sync.
- Real ratio parsing. You type the dilution the way it is printed on the bottle, 1+9 or 1:9, instead of converting it to a percentage in your head.
- Honest about approximation. The temperature, push, and reciprocity numbers are established guideline values. They are a strong starting point you confirm against your own negative, not a guarantee.
EditMe is free to download. Some pro tools are part of an optional EditMe Pro subscription, and the app runs on iPhone and iPad.
How it compares
| Factor | EditMe | Working by hand |
|---|---|---|
| Temperature compensation | Adjusts time from your reference to the measured temperature | Read a printed time-temperature chart, interpolate yourself |
| Push and pull | Separate per-stop factors for black and white and C-41 | A single rule of thumb applied to every film |
| Dilution | Parses 1+9 or 1:9 and returns ml of concentrate and water | Mental arithmetic at the graduated cylinder |
| Reciprocity | Per-film correction that engages above one second | Look up a film-specific table, apply the exponent by hand |
| Print test strip | Even f-stop bands with per-band and total seconds | Linear guesses or a separate timer |
| Where it runs | On the iPhone, offline, no account | A wall chart or a website you cannot reach in the dark |
Frequently asked questions
Do the calculators work without a connection?
Yes. All five are plain functions that run on your iPhone, so they return the same result every time with no signal and no account.
What dilution formats can I type?
You can enter a ratio as 1+9 or 1:9, or choose Stock for undiluted. EditMe splits your total volume into millilitres of concentrate and water.
Does push and pull treat colour film differently from black and white?
Yes. Push and pull uses separate per-stop factors for black and white and for C-41, because C-41 responds more weakly to a longer first developer.
When does the reciprocity correction kick in?
Only above one second. Below that, reciprocity failure is not relevant, so the metered time is returned unchanged. Above it, the time is raised to the chosen film's reciprocity exponent.
Are the times exact?
They are established guideline values and approximations, meant as a reliable starting point. You still confirm against your own negative, since chemistry, agitation, and equipment vary.
Is EditMe free?
EditMe is free to download. Some pro tools are part of an optional EditMe Pro subscription, and it runs on iPhone and iPad.