Jobo Expert Drum question

[Don Wallace]

This is likely a very stupid question. I hope not. I hate looking like a dork.

I have been processing 4x5 in my CPE-2 and recently borrowed an Expert Drum for 5x7 and 8x10. I will be hand-rolling this on the Jobo base. I use HC-110, directly from the syrup, in a variety of dilutions. I have calculated, with help from Michael Covington's unofficial HC-110 page, that I need a minimum of 4ml of syrup per sheet of 4x5. In the 4x5 drum on the CPE, all sheets use the total amount of the developer. They are all "in it together" so to speak. However, on the Expert Drum, it appears that the total amount of developer gets divided into the various cylinders (five in my case). So, if I am only developing one sheet in the Expert Drum, that particular cylinder would only get 1/5 of the total solution. If I had prepared sufficient solution for only one sheet, then this sheet would not get enough of the developer to do the right job.

Is this right or am I missing something SO obvious that I will be required to wear the group dunce cap?

[Tom Westbrook]

Check the www.jobousadarkroom.com/products/3000.htm (http://www.jobousadarkroom.com/products/3000.htm) web page for the manual on the expert drums. There is a mimimun (and a max) solution quantity that has to me maintained. Beyond that, you just figure quantity per sheet as you were doing above up to the maximum solution volume. The soup sloshes around among all the little tubes and isn't trapped to individual tubes.

[Simon Knight]

With the Jobo drums you must worry about two things:

1. You need enough developer to fully develop the film. This is dependent on the devoper of your choice.

2. You need enough volume of liquid in the drum as specified by Jobo. Each drum has a minimum. If you are using a 3005 then the minimum is 270ml. Next, they recommend a certain minimum volume per sheet so 4 or 5 sheets of 5x7 may exceed the minimum.

i.e for one sheet of 5x7 in a 3005 you need a minimum of 270ml of diluted developer. The developer does circulate between all the cylinders assuming developing time is more than 5 minutes. Jobo does recommend using these drums at least half full of film, but I have developed 1 or 2 sheets of 8x10 without a problem.

[Joseph O'Neil]

I use the Jobo 2551 drum (two reels, 4x5) andHC-110 from direct syrup. I use 700ml of water, and exactly 10ml of pure syrup. I do 8 sheets at a time.

I use this amount for Tri-X, HP5+, Forte Pan, and a few other B&W films, and never had a problem. 3-4 minue water pre-soak, and average developing time of around 10 minutes, whne at 70 degrees F.

Your milage will vary.

I used to use individual drums myself some years ago, one sheet at a time, but I found I needed a minium of 4-5 ml of syrup to do one sheet of film. Exactly why you need 4ml for one sheet, while 10ml does 8 sheets - I'll let the chemists on this forum explain. But that's what I found.

So if doing "bulk" - try keeping your solution down lower if you can. I find higher solutions, especially with HC-110, regardless of how short you cut down your time, can "burn" the film, certianly overcook it.

joe

[Stan. Laurenson-Batten]

I regularly develop a single sheet of 10X8 in my Expert drum on the Cpp2. I have found that using TMax RS or Rodinal 1:9 a working dilution giving 3ooml of total liquid works fine. I enjoy sparkling fully processed negatives every time. For more than two sheets of 10X8 I would bum up the total to about double.
Not having any experience, I cannot say if this works on hand rolling but I cannot see any reason why not. You question is valid and certainly not stupid as on inspection of the 3005 drum, and others of the Expert drum group, there does not appear to be any liquid freeway between cylinders - whch of course there is.

[Don Wallace]

Thanks for the all the quick answers, and a special thanks to Stan for making me look not quite so dim.

[ronald moravec]

As the drum revolves, the liquid flows to the lowest point. It does not divide itself among the various compartments