Agitate › Push and pull
Rating a film away from box speed
Push Processing Times on iPhone
A published push time beats a formula every time, and the spread between them is wide enough that it matters. Agitate looks for the row first, and says so plainly when it has to fall back on a factor.
The published row wins outright
Of the 795 development times bundled with the app, 252 are for an exposure index away from box speed: 184 pushed and 68 pulled. When you ask for an exposure index that one of those rows covers, that row is the answer. No factor is applied on top of it, and nothing is scaled.
- 184published push rows
- 68published pull rows
- 543rows at box speed
Your exposure index follows from the box speed and the stops: one stop of push doubles it, two stops quadruple it. The app shows the resulting index next to the label so a push of two on an ISO 400 film reads as what you actually set on the camera.
When there is no published row, the number is labeled an estimate
Real published factors for a single stop of push run from roughly 1.07 times the base time to about 1.58 times it, depending on the film, the developer and the dilution. A single multiplier is a poor substitute for a datasheet, and an app that hides that behind a confident looking time is teaching you to trust the wrong thing.
So Agitate applies a generic factor only when nothing published matches, and marks the result as an estimate wherever it appears. The factors sit in the middle of the published spread and differ by process, because the processes do not behave alike.
| Process | Per stop pushed | Per stop pulled |
|---|---|---|
| Black and white | 1.33 × | 0.80 × |
| C-41 | 1.35 × | 0.80 × |
| E-6 | 1.33 × | 0.75 × |
Used only when no published row covers the exposure index you asked for. Anything derived this way is shown as an estimate, never as a manufacturer figure.
Where the extra time goes
A push is not a scaling of the whole run, and treating it as one quietly stretches baths that were never meant to move. Agitate applies the change to the bath that carries it and leaves every other one at its published time.
| Process | The bath that moves |
|---|---|
| Black and white | The developer, or the monobath |
| C-41 | The developer only. Bleach, blix, fix, wash and stabilizer keep the kit's time |
| E-6 | The first developer only, and the change is film independent |
The three processes are covered by the one app, so a push on a roll of color negative is handled by the same screen as a push on black and white. C-41 in the app. E-6 in the app.
A push survives the thermometer
Reading the thermometer part way through a push is where other timers lose the run. Agitate converts the time the run is actually using rather than the raw figure in the recipe, which means your push, your pull and the surcharge for re-used developer all survive the correction. Two readings compose, so going back to the first temperature gives back the first time. How the conversion works.
And if a push takes your development past a point where you want a record of it, that is what the journal in Agitate Pro is for: the film, the recipe, the temperature you actually measured, the push and your own note, searchable, and exportable as CSV and JSON.
Push times that tell you where they came from
252 published rows off box speed, an honest estimate label when there is no row, and the change applied to the one bath that carries it.
Agitate for iPhone and iPad
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