Results 1 to 10 of 10

Thread: Rotary Processors and Dilute Developers

  1. #1

    Rotary Processors and Dilute Developers

    The effectiveness of utilizing rotary processory such as the JOBO CPA2 and CPP2 for extended development times with dilute developers has been questioned by Bar nbaum because of the inability of the film to be idle in the developer for perio ds of time. Has anyone experience on this subject that they could impart? Do you go to tanks for this application or have you found a technique to use your JOBO ?

    I know Sexton has been a strong proponent of the JOBO and uses extended developm ent with dilute developers, but I could not find literature that covered this su bject from him.

    Thanks in advance.

  2. #2

    Join Date
    Dec 1999
    Forest Grove, Ore.

    Rotary Processors and Dilute Developers

    How is it that a Jobo system can maintain the same temperature inside the drum that is being carefully maintained in the bath, when the spinning drum must constantly be bringing water up on the top of the drum? I would think that the water's exposure to air, and it's movement with respect to the air, would cause the water to evaporate, thus cooling the drum?

  3. #3

    Join Date
    Nov 1998

    Rotary Processors and Dilute Developers

    I can effectively get a N-2 development from a rotary processor. For more contraction than that it is necessary to go to a tray where the agitation can be controlled. John Sexton does like the JOBO system but for many of his long exposures with a very high subject brightness range he still uses tray development with very little agitation.

  4. #4

    Join Date
    Mar 1999

    Rotary Processors and Dilute Developers

    The only reliable way I have found to change curve shape for a given film-developer combination is to alter agitation patterns. Changing dilution alone without altering the associated agitation pattern does not change the curve shape appreciably. In other words, using more dilute developers and extending time without changing agitation yields the same characteristic curve. The other alternative is to formulate different developers for different curve shapes. Good luck. DJ

  5. #5

    Rotary Processors and Dilute Developers

    The other alternative is to formulate different developers for different curve shapes.

    Good idea. I don't think this is persued enough@

  6. #6

    Rotary Processors and Dilute Developers

    I don't think dilution produces a shoulder (highlight compensation) with many film/developer combinations. I have heard that dilution is not as effective with modern films, as it was with older emulsions. I have seen published tests using various dilutions of HC-110 with T- Max 100, and all dilutions produced identical curve shapes when developing to the same contrast.

    To get a shoulder, use a developer that produces a shoulder. I use D- 23 1:1 in my Jobo CPP-2, and I get a mild shoulder that begins at Zone VII with HP-5+. N-4 development works in the Jobo with this combination. If you don't want to mix your own developer, Microdol-X is similar to D-23, except Microdol-X includes 30g Sodium Chloride per liter. Table salt is a silver solvent.

  7. #7

    Rotary Processors and Dilute Developers

    I have found since using my Unicolor drum that it is difficult to get any compensating action unless I go to extreme dilutions. By compensating action I am talking of N-2 or more. When I took John Sextons workshop he used the Jobo drum for small amounts of contraction but went to a device he called a slosher to acheive more than N-2 contractions. The new thin emulsion films like TMax and Delta films don't have enough emulsion to hold enough developer to accomplish extreme contraction. The developer exhausts at an even rate regardless of how much converted silver halide is present. The films such as Tri-X and FP4/Hp5 are good at contraction because the emulsion holds more active developer. Agitation plays an extremely important roll in compensating type development. The more contraction you want the longer you let the film stand in the developer without agitation. The same thing happens with a waterbath type development scheme. Changing developers only changes the slope of the curve. For a given film, agitation and time in contact with developer is the way to compensate for contrast. James

  8. #8

    Join Date
    Nov 1998

    Rotary Processors and Dilute Developers

    I've found that different developers with the exception of pyro only very modera tely affect curve _shape_ of HP5+ and Delta 100, and that agitation, whether con tinuous or intermittent as long as it's sufficient for satisfactory evenness, ma kes hardly any difference. By "satisfactory evenness," I mean that development e venness is _no different_ than that obtained by continuous or my standard invers ion technique.

    Note that development techniques that require the film to be idle for long per iods of time usually result in rather uneven development.

    It's very easy to alter the CI of these films, but the basic curve shape stays the same.

    Pyro otoh puts an extreme shoulder into HP5+, whether it's measured for ordina ry optical density or blue-filter density...but that's not necessarily a good th ing. A very strong shoulder also provides what's commonly known as blocked highl ights, i.e. there's no significant increase in density with increased exposure, or iow, very low highlight contrast.

    I believe what Sexton is doing is using a developer diluted much more than nor mal rather than shortening the development time, and using constant rotary agita tion to ensure good evenness. It certainly works fine for decreasing CI and main taining even development although it has minimal effect on curve shape.

    I wonder Barnbaum hopes to accomplish with idle time and whether or not he's a ctually ever measured test negs to see if it has any effect.

  9. #9

    Rotary Processors and Dilute Developers

    I happen to have John Sexton's workshop handout on extreme contractions at hand. He uses T-MaxRS developer diluted 1:15 from concentrate (not stock)at 75 degrees with T-Max 100 film rated at EI-40 (vs. his usual 64 for normal development). He develops in the slosher (not the Jobo) with an agitation scheme of constant gentle agitation for the first minute, 5 sec. agitation every 30 sec. for the next minute, no agitation for 2 minutes followed by 10 sec. gentle agitation every 2 minutes. He develops 8-11 minutes. He notes that you should expect the developed negs to have a warm color (I've also observed this). He says "I have had amazing success handling extreme contrast situations . . . .In recent work I have encountered lighting conditions with as much as 15 stop contrast range."

  10. #10

    Rotary Processors and Dilute Developers

    If you want to lower contrast, the real way to do it is use a low- contrast developer. I know of two, Kodak Technidol and POTA. Both use phenidone at the developer. With these developers, you can process in the Jobo and get down to N-6 and possibly further. This is explained in further detail in my website

    Al Robinson

Similar Threads

  1. Highly Dilute Paper Negative Development for 8x10?
    By Michael Heald in forum Darkroom: Film, Processing & Printing
    Replies: 8
    Last Post: 5-Dec-2005, 02:02
  2. tri-x in xtol development time (can you dilute?)
    By dan otranto in forum Darkroom: Film, Processing & Printing
    Replies: 6
    Last Post: 5-Mar-2005, 13:36
  3. Dilute developer in Jobo drums
    By bob moulton in forum Digital Hardware
    Replies: 7
    Last Post: 13-Jan-2002, 10:21
  4. TMX and dilute XTOL (1:3)
    By Keith Baker in forum Darkroom: Film, Processing & Printing
    Replies: 5
    Last Post: 4-May-2001, 19:21
  5. 5X7 daylight processors
    By Douglasa A. Benson in forum Darkroom: Film, Processing & Printing
    Replies: 4
    Last Post: 15-Aug-2000, 19:15


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts