Dilution of developer in a Jobo tank

Quick question: If one is developing two rolls of film in one of the Jobo tanks ( using "one shot developer" ) does one need to use more developer ( less of a dilution ) then if one is using only one reel with one roll of film ( and the other reel also in the tank of course simply to insure that the volume is correct )? Same question if one is using any tank,, e.g., a Patterson Tank....more reels with more film, does the equation read more developer? The reason for my asking is that I developed some low speed Ilford ( Deltoa Pro 100 ) in my Jobo CPE2 ( using Ilfosol S for the first time ) with the usual careful attention to time, temperature, etc. and the negatives were notably thinner then I am used to seeing. I have yet to develop multiple rolls of TMax or Delta 400 Pro ( I usually use DDX for these films ) in the Jobo, and now I am just abit hesitant to do so. I appreciate the help.

Edwin

In rotary the min amount of developer is

1) Set by the tank. Different takes have different min levels of developer.

2) The developer. One needs to use enough developer to develop the film.

You should use at least the higher of the two numbers.

I use only hand agitation for developing, that is I don't use Jobo processor, so...

As far as I know you need to use enough volume of developer, in your standard dilution.

So, if you for example use 250ml of 1:1 dilution for developing 1 film, when you develop 2 films you will use also 1:1 dilution, but 500 ml instead of 250 ml. When I develop my films I use allways between 500 and 600 ml of developer. But, again, I don't use processor...

Dear Edwin,

When I decide to use a high dilution I use a larger tank. I have three tanks, 251X, 252X and 255X and have developed using Xtol up to 1:3.

Neal Wydra

Thanks haris! Thus, in effect, you are using "two portions" of developer at the "correct dilution" for two rolls of film. Easily understood. And Neal, as I understand your response, you also increase the volume of developer at the "correct concentration" for multiple rolls of film, i.e., the more reels, the greater the volume at the same concentration in A LARGER tank.. However, I do not read the Jobo manual as stating that one increases the amount of solution if one has two reels in the same size tank. With the Jobo, one has a volume of solution that the tank holds for rotation and inversion processing-and assuming one stays with the SAME tank for two reels of film the volume DOES NOT increase. Thus, one is, in effect , using one half the correct amount of developer ( same concentration and volume, but now two rolls of film ). The reasonable conclusion is that one must increase the time of devlopment, or once must change the dilution so that more developer is available, n'est ce pas? Unfortunately, I see no clear cut guidance in the Jobo manual. Perhaps I've missed something?

The Jobo manual is not the place to find this info. Read the developer manufacturer's data sheets. They will tell you how much developer concentrate/stock solution is required per roll of film. Whatever size tank you use, you need that amount of developer stock in it (at a minimum).

This can be a problem if you use a highly diluted developer such as Rodinal. You need 10ml of Rodinal stock solution per film according to the Agfa data sheet. Therefore if you dilute it at 1+50 you need 510ml of working strength per roll of film. If you use it at 1+25 you only need 260ml working strength per roll.

You can normally use the same amount of developer for two rolls but as said, you will need to increase development time. Again, the manufacturer's data sheets should give the necessary information.

Cheers, Bob.

Dear Edwin,

My solution involves using a larger tank. Obviously, if you use the same tank you can't put more solution in. If you do not have a larger tank available, this solution is not open to you.

Neal Wydra

Thanks to Neal and all of the others who took time to respond. It is now apparent that I will have to double the amount of developer at what-ever dilution is chosen with changes in time ( if any ) as dictated by the concentration of the developer. Great group here, and once again, Vielen Danke!

Edwin Mahler from Hamburg