Rotary Processors and Dilute Developersgreenspun.com : LUSENET : Large format photography : One Thread
The effectiveness of utilizing rotary processory such as the JOBO CPA2 and CPP2 for extended development times with dilute developers has been questioned by Barnbaum because of the inability of the film to be idle in the developer for periods 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 development with dilute developers, but I could not find literature that covered this subject from him.
Thanks in advance.
-- Michael Kadillak (email@example.com), August 15, 2000
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?
-- neil poulsen (firstname.lastname@example.org), August 15, 2000.
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.
-- Jeff White (email@example.com), August 15, 2000.
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
-- N Dhananjay (firstname.lastname@example.org), August 15, 2000.
The other alternative is to formulate different developers for different curve shapes.
Good idea. I don't think this is persued enough@
-- David Stein (DFStein@aol.com), August 15, 2000.
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.
-- William Marderness (email@example.com), August 15, 2000.
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
-- james (firstname.lastname@example.org), August 15, 2000.
I've found that different developers with the exception of pyro only very moderately affect curve _shape_ of HP5+ and Delta 100, and that agitation, whether continuous or intermittent as long as it's sufficient for satisfactory evenness, makes hardly any difference. By "satisfactory evenness," I mean that development evenness is _no different_ than that obtained by continuous or my standard inversion technique.
Note that development techniques that require the film to be idle for long periods 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 ordinary optical density or blue-filter density...but that's not necessarily a good thing. A very strong shoulder also provides what's commonly known as blocked highlights, 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 normal rather than shortening the development time, and using constant rotary agitation to ensure good evenness. It certainly works fine for decreasing CI and maintaining 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 actually ever measured test negs to see if it has any effect.
-- John Hicks (email@example.com), August 16, 2000.
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."
-- Chris Patti (firstname.lastname@example.org), August 16, 2000.
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 www.vsta.com/~alrob.
-- Al Robinson (email@example.com), November 22, 2000.