Wow, Thanks for the neat info. So how do you compensate for the 2 films in one tank? double the strength of the developer? Sorry for the noobish question.
I have the same question, so don't feel noobish. If i'm using Pyrocat, would I double the strength...hmmm
Not a bad question at all.
The answer varies with the developer being used.
When you develop in a tank, you usually determine the amount of working strength developer by measuring how much is required to cover the reels.
For some developers, that amount is actually a bit wasteful, because it may contain enough chemical "capacity" to develop more rolls than are actually loaded.
For other (usually more dilute) developers, the amount required to cover the reels isn't actually enough to ensure full development, because you need more of the original stock chemistry than is present in the diluted working solution.
To determine whether or not you need to change either the total amount of working strength developer in the tank, or the dilution used, you need to look at the capacity figures for that developer. They are usually expressed in terms of how many 8x10 sheets/120 rolls/35mm 36exp rolls can be developed using an amount (1 liter?) of stock solution of that developer.
So if you are using your developer at "stock" dilution, and the data from the manufacturer indicates, e.g., that 1 liter of stock developer has the capacity to develop 4 rolls of 120, you know that each roll needs at least 250 ml to be sure of full development. So in that situation if you have two rolls of 120 on the reel, you need to be sure that you use at least 500 ml of stock developer - more if you need the extra quantity to cover the reel sufficiently.
If you use a dilution of your developer that is different from stock, you need to factor that difference into the capacity calculation.
Using HC110 as an example (because that is what I use) if you do the calculation, the Kodak indicated capacity figures work out to a capacity that requires at least 6ml of the original concentrate for each roll of 120. I use a 1+49 dilution of HC110 (essentially the same as dilution "E"), so that calculates out to 300 ml of working solution per 120 roll. So if I'm developing two rolls on a reel, I need at least 600 ml of working solution at that dilution. Conveniently, one of my tanks requires 590 ml to cover that reel - so it works perfectly.
Hope this helps.
