Jobo "universal offset" for converting b&w tank agitation to continuous?

OK, I have been piling back through the Jobo postings on APUG and can find lots of, " I use HC110B, Rodinal 1:50, 1:75, etc, etc, but almost NONE of the postings give film types or times!

Has anyone come up with a good rule of thumb to convert tank agitation @ 68 degrees F to 75 rpm continuous rotation on a Jobo @ 75 degrees F?

I am going to have to assume automatically that dilution rates will be much higher OR a restrainer like bromide will have to be added to keep from cooking the negatives; true?

I would like to process Arista 120 x 400 ISO, Ilford 120 Delta 100, and TMax 100 35mm film in a 1500 series tank (of course, not all at once) and am looking for a starting point for any or all of them.

I prefer HC110, BUT do have Rodinal, D76 and Pyrocat HD as other options...

I would be happy to compile a list of known good combinations of B&W chemistry and film in the Jobo and place it in the articles section if everyone will share their knowledge.

Kino

You shouldn't have any trouble. But it will be different.
And, because this is photography, different combinations will respond differently.
Use a 20% reduction in time as a starting point.

If you use .1+fbf at Zone 1 as a measuring stick, you may think you're getting something you're not: the curve shape changes with SOME developers, and not with others. Rodinal develops an abrupt transition from II to V. Which CAN be cool, but it ain't what you get with 1 minute cycles, or especially 5 minute cycles.

Anyhow, you'll have fun. More fun if you evaluate the negative by printing it, not using a dense-o-meter.

don

df cardwell said:

Kino

You shouldn't have any trouble. But it will be different.
And, because this is photography, different combinations will respond differently.
Use a 20% reduction in time as a starting point.

If you use .1+fbf at Zone 1 as a measuring stick, you may think you're getting something you're not: the curve shape changes with SOME developers, and not with others. Rodinal develops an abrupt transition from II to V. Which CAN be cool, but it ain't what you get with 1 minute cycles, or especially 5 minute cycles.

Anyhow, you'll have fun. More fun if you evaluate the negative by printing it, not using a dense-o-meter.

don

Click to expand...

Thanks Don, that sounds like a reasonable starting place.

Yes, using a densitometer and sensitometer can be drugery, but I might have to resort to it to get the scoop on how it all falls apart on either end of the curve when you twist it's tail...

Jobo asserts that a water prebath somehow offsets contrast buildup but I don't think so...

I am trying to search the Jobo site for old issues of "The Journal of Rotary Processing" or some such, but cannot find them.

I do believe PE mentions them in an old thread; PE? Still know where they are or where I can find a copy of them online?

FWIW, I follow Jobo's instructions. Jobo advises that, if you prerinse your negatives for five minutes before adding developer, you should use your ordinary b+w recipe, without any adjustments.

So, that is what I have done, and it has worked for me. I am using Rodinal in 1:25 to 1:50 dilutions with TXP sheet film, in 2500-series (4x5) and 3000-series (5x7) Jobo tanks.

Try a tank of negatives as Jobo recommends and see if it works for you.

Sanders McNew
www.mcnew.net/portraits

The unblinkingeye website has an article on this. From the tests done it varies from no change to shorter to longer. While you could use a rule of thumb to start it seems to me the only thing that really works is testing.

Ilford's site quotes reduction times which differ from others quoted here but not so much as meaning the difference between superb negs and disastrous ones. The difference between 20% and say 15% reduction on a 10 min dev time is only 30 secs. Enough for a difference in the neg but not enough to make either unprintable.

That's not to to say Ilford is right and others are wrong. It's what works for you but it may mean a little experimenting. If top class negs to your eaxct liking are important from the start then there's an argument for "wasting" a roll on unimportant shots before deciding on "correct" Jobo times. A bulk loader and short rolls are ideal here.Incidentally I once wrote to Ed Buffalo about Rodinal and continuous agitation. He was good enough to reply and said that he had never used this combo and didn't recommend it if the aim is to take advantage of Rodinal's acutance.

pentaxuser

pentaxuser said:

The difference between 20% and say 15% reduction on a 10 min dev time is only 30 secs. Enough for a difference in the neg but not enough to make either unprintable. ...

That's not to to say Ilford is right and others are wrong. It's what works for you but it may mean a little experimenting. If top class negs to your eaxct liking are important from the start then there's an argument for "wasting" a roll on unimportant shots before deciding on "correct" Jobo times. A bulk loader and short rolls are ideal here.Incidentally I once wrote to Ed Buffalo about Rodinal and continuous agitation. He was good enough to reply and said that he had never used this combo and didn't recommend it if the aim is to take advantage of Rodinal's acutance.

Click to expand...

I would add only that, in a ten-minute Rodinal bath, I'm not sure you'd see a difference in a 30-second variation in development. I say this after goofing more than a few tanks of film over the years (forgetting to set a timer, or setting it wrong, or being out of the room when the timer went off) and finding that the results are not nearly so sensitive to the formulae as I had imagined. There are so many variables in exposing and processing film -- meter accuracy, meter technique, shutter accuracy, thermometer accuracy, and so on -- that minor differences in bath times are the least of your worries. Which of course is why the best advice, maddening for a newcomer to hear, is try it yourself and adjust as needed.

As for Ed's remark, again, I have huge respect for the man, but by his own remarks he offered the advice without having any experience to support it.

Sanders.

Sanders. I wouldn't disagree with anything you said. The originator really only wanted a rough rule to apply to the conversion and between all of us we gave it to him. In addition he may or may not have wanted a warm feeling that slight deviations in the rule didn't mean the difference between fantastic success and abject failure which is what my comments and yours even more so reflect.

There is always a tendency for threads connected to such issues to become black and white( right or wrong) matters between posters( good pun eh?)

To inject a note of humour we have a comedian in the UK called Jasper Carrott who tells a story of trying to rid his garden of a mole. By asking 50 experts he discovered that there was only one way to get rid of a mole - all of them different!

pentaxuser

I mostly soup Ilford films in my Jobo CPP-2 with Ilfosol-S.
I am new to this and still refining my developing, haven't used a densitometer yet.

My "trick" is to use Ilford's temperture-time adjustment chart and drop the time by one degree celcius, then go from there. For example, FP4+ in Ilfosol-S 1-9 at 125asa needs about 6,30 mins normally at 20c, I develop it in 6 mins which would be the time at 21c.
Seems to work well so far.

We have the times already charted for Jobo, Wyng Lynch, and Phototherm processors for most films and our F 76 plus Developer. We've never had to convert to contiuous adgitation.

Thanks a lot everyone; I got blind-sided by Hazmat and EPA inspections this week at work, had a huge power surge that killed our fire supression system and on top of that, had the property manager out doing a complete inventory of two buildings and a storage facility and was too tired to respond to all the helpful tips.

Thanks again...

UPDATE: Today, after shooting a normally rated roll of B&W Arista EDU Ultra 400 ISO 120 film as a test, I processed it in the jobo for 3:30 @ 75 F in HC110B and found that the density of a grey card in the scene measured in the .70 -.80 visual density range (as it should), BUT noted also that the shadows didn't quite have enough guts for me, so I think I will be rating this film @ 200 ISO in the future OR not compensating for the temperature difference between 68 and 75 degrees.

I used the nomograph in Anchell's "Darkroom Cookbook" and brought the normal development time from 5:00 to 3:30, but that appears to be offset by the 5 minute prewash. It really surprised me, I had no faith at all that the 5 minute prebath would affect speed that much, but it certainly appears to have done so.

No scans yet because; 1. My scanner sucks and does not have a trans head. 2. My enlarger head gasket welded itself to the bottom plate and requires a full teardown, cleanup and replacement of the gasket, and I don't have the parts laying around, so no contact sheets yet.

Once I get a good contact sheet, I should be better able to assess the actual results from bracketing up and down 2 stops from "normal" as determined by the Kiev 88 meter, but for now, peering through that irritating blue base, it looks like the +1 stop is the best for density.

You would have thought the 5 minute prewash would remove more of the blue dye but it did not...