View Full Version : Very slow JOBO rotation - anyone tried it?

Kevin M Bourque
21-Dec-2005, 10:08
Hi All -

Why would I want my JOBO to spin very slowly....two possible reasons.

First, some hold the opinion that constant agitation reduces sharpness (no edge effects).

Second, Pyro can supposedly be a problem in a JOBO because the fast rotation causes it to oxidize. I never tried Pyro in a JOBO so I can't comment on that.

Here's my idea. Pre-wet the film, drain and add the developer. Give the tank one good turn to get all the film exposed to the liquid. Start the tank turning very slowly (one or two rpm or there abouts). The film will spend most of its time out of the developer but it won't have time to dry out. It might even have some kind of compensating effect. I'm not sure how much effect this will have on oxidation.

I plan to give this a try next time I have some time, but I wanted to ask around first. I'll expose a few sheets in the enlarger and spin the thing by hand.

I use the film reel that holds six sheets, not the expert drum.

The thought occurred to me that if this was a good idea, the JOBO would have an option to spin at these speeds. So, just in case it's a dumb idea.....be nice!

Denis Pleic
21-Dec-2005, 10:25
Kevin, you might run into some problems using slow rotation speeds.

I had some problems with my 4x5 negs in Jobo CPE (old one, which has two speeds, marked "1" and "2"), like streaking and uneven development, until I decided to go for higher speed. With higher speed rotation my problems vanished.

I'm also using the 2509N reels like you, in 2523 tank, which takes one 4x5 reel. I always develop max. 4 negatives. The developer I use is Rodinal, diluted to about 1+60.



Arne Croell
21-Dec-2005, 10:43
I used the lowest setting on my CPP-2 years ago for HP5+in PMK, to reduce oxidation as you said . No streaks or uneven development. I still used the split developer technique in addition. One secret is to keep the water level low in the upper tray, where the drum rotates, to reduce the overall liquid mass the motor has to move. A small amount of water in the drum is enough to keep the temperature.

Ken Lee
21-Dec-2005, 11:32
How slow is slow ?

When I used my JOBO, I rotated it by hand, and not at breakneck speed. I never saw any problems.

Bruce Watson
21-Dec-2005, 12:10
I've heard that Gordon Hutchings uses a Jobo for his PMK work. I don't think he'd do that if he found oxidation to be a problem. Ask around in that direction and see what you can find.

My CPP-2 won't rotate that slowly I'm pretty sure. I use about 30 RPM, which is below "F" and above "0" (off) on the speed dial. It's been a few years since I played with rotational speed, but I seem to recall that my CPP-2 got flakey (as in unpredictable) with speeds below about 25 rpm. I'm sure YMMV though.

Michael Gordon
21-Dec-2005, 12:44
I use a Jobo 3010 with Rollo Pyro and spin it (no pre-wet) on an old Chromega dual-action agitator (not sure of the RPM, but it's not too fast). With Ilford Delta and Fuji Acros I have always gotten perfect development with incredible sharpness.

ronald moravec
21-Dec-2005, 12:55
Gordon uses a nitrogen blanket pumped down the lift to slow or stop oxidation. With all the government rules on gas storage tanks tanks, I don`t think you want to get into that.

I run my expert drum on high for 30` , then to medium for 30 more, then to film speed for the balance of the time. It works for D76 and Hc110.

PMK oxodizes like crazy and two complete replacements during the development did not help.
I think Rollo Polo was designed for rotation development.

PMK works best for me in a sealed Nikor tankup to 4x5 size. It comes out looking as fresh as it went in. Trays and open tanks allow ozidation, but not as much as rotation.

Keith Pitman
21-Dec-2005, 15:14
For PMK, I run my Jobo (using expert drum) at the slowest speed (below 1). I've had not problems with this. For plus development, I replace the developer half way through the cycle.

Eric Woodbury
22-Dec-2005, 11:06
I'm using Jobo 3xxx series drums on a rotary base (non-Jobo). It's probably 10 to 12 rpm. For extra insurance, I backfill the tank with nitrogen at the beginning of development and put a cork in the fill hole. The PMK does not, can not, oxydize. The developer comes out of the tank looking like weak ice tea. Been doing this for about 15 years. Works fine.

Ken Lee
22-Dec-2005, 14:48
"Been doing this for about 15 years".

Geez... You must be exhausted !

I'm sure the film must have developed by now. Enough already !

What is that... N+ One Million ?