ID-11 Stock: Development Time for Simultaneous Processing of Multiple Rolls

There are many unknowns - from the amount of working solution you use per batch to the types of films you process. If you use rotary processing, things may need to be considered more carefully, but with inversion agitation and a full tank I don't think there will be a problem, unless the developer is completely exhausted. But this isn’t a developer that just dies suddenly.

Filippo Romani said:

In other words: does simultaneous development count as a single use of the developer, or does the increased film load require a time correction?

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Simultaneous development counts as single use. Be aware that for a second use, you have to add two times 10% development time when you have developed 2 films in it.

It's the same development time regardless of the number of films developed at the same time.

Adjustments are needed before the next batch

Ian

The additional time is per batch.
You are adding (I assume) more developer for each roll in the batch so there is no compensation for exhaustion.

Dr. no said:

The additional time is per batch.
You are adding (I assume) more developer for each roll in the batch so there is no compensation for exhaustion.

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This is essentially correct, although one needs to be aware of how this impacts further use.
It is quite likely that the volume of fresh developer you are using in your developing tank has more than enough capacity to develop a single roll.
The reason that Ilford (Harman) recommends the time increase with subsequent rolls is as much or more to do with the development byproducts added to the mix as you develop film as it has to do with exhaustion per se.
Ilford (Harman) provide data indicating that a litre of ID-11stock has the capacity to develop 10 rolls of film, with time compensation. That indicates that if you have at least 100 ml of fresh stock ID-11 per roll in your tank, then you should be able o develop each roll at the basic standard time.
If, as an example, you develop 3 rolls in at least 300 ml of stock, and then re-use that stock, you should calculate the necessary time adjustment for subsequent rolls based on having already used the stock for three rolls, not one.
In other words, if fresh developer was used initially for three rolls, in your next batch of developing use the time adjustment for the fourth roll.

Ian Grant said:

It's the same development time regardless of the number of films developed at the same time.

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Edit: I finally realized Matt has written what I said below much better and detailed. I leave it here anyway:

That's correct, the only thing to keep in mind is, that with Ilford ID11 and Kodak D76 there is a minimal amount of stock-solution needed for every film or there is another compensating factor to be added. From my head it is 100 ml of stock solution per film for ID100 and 200 ml for D76. Afair it's about 10% added in normal sized tanks and will often go unnoticed but better consult the datasheet.