How does film ISO affect black-and-white development time?
Asked 4/4/2017
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If I use the same black-and-white developer, how does development time change for films rated at ISO 100, 200, 400, or 800? I’m also unsure whether this is different when using a faster film versus pushing a slower film to a higher ISO. Does the amount or dilution of developer change too, or mainly the time?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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Have you read your developer/film manual? Usually if you are pushing film (ISO100 film shot as ISO400 for example) you need to increase development time. The relation is not linear and depends on film-developer combination.
For example, you can see how Ilford specifies its Delta 3200 development time depends on ISO setting that you used to shoot film ("meter setting"):
As you can see here, dilution of developer (first column, "1+4", "1+15" etc) increases required development time.
In practice, you should find out development setting that gives you the result you want, starting with manufacturer's information for your film.
Originally by user38691. Source · Licensed CC BY-SA 4.0
user38691
9y ago
0
Generated from our catalog & community — verify before relying on it.
Development time is not determined by ISO alone, so there isn’t a simple 100→200→400 linear rule. It depends on the specific film, the developer, its dilution, the temperature, and whether you are using the film at its box speed or pushing it.
In general:
- Faster films or pushed film often need longer development.
- More diluted developer also usually needs longer development.
- The required amount of developer is usually set by the tank and minimum chemistry requirements; what commonly changes is dilution and time, not just “more chemicals.”
If you mean pushing a film — for example, shooting ISO 100 film as if it were ISO 400 — you typically increase development time, but the exact increase depends on the film/developer combination.
Best practice is to use the manufacturer’s data sheet or development chart for your exact film and developer. Those charts give the recommended time, temperature, and dilution for each film speed or meter setting. Start there, then adjust only if you are trying to fine-tune the look of your negatives.
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