Question about Jobo tanks

[Jay DeFehr]

I'm currently finishing up a tank of my own design, for processing one or two sheets of 4x5 film in 35ml of solution, with intermittent agitation. I don't know yet if it will develop film evenly. I'll test it when I go home. The design is a kind of cross between a slot processor and a JOBO. The film is loaded into a slot (certainly the easiest loading tank), and the developer is introduced by gravity and fills from the bottom of the tank. Agitation is accomplished by air displacing the developer solution intermittently, the way solutions are forced out of the JOBO solution bottles. My little prototype is very simple and air is supplied by me breathing into a tube, but it has the potential for automation. The tank is smaller than a 4x5 film holder, and could be used in series, with individual automation, but that's getting ahead of myself. If it provides even development, I'll go forward and refine the design. If not, it's back to the drawing board.

[rdenney]

I'm currently finishing up a tank of my own design, for processing one or two sheets of 4x5 film in 35ml of solution, with intermittent agitation. I don't know yet if it will develop film evenly. I'll test it when I go home. The design is a kind of cross between a slot processor and a JOBO. The film is loaded into a slot (certainly the easiest loading tank), and the developer is introduced by gravity and fills from the bottom of the tank. Agitation is accomplished by air displacing the developer solution intermittently, the way solutions are forced out of the JOBO solution bottles. My little prototype is very simple and air is supplied by me breathing into a tube, but it has the potential for automation. The tank is smaller than a 4x5 film holder, and could be used in series, with individual automation, but that's getting ahead of myself. If it provides even development, I'll go forward and refine the design. If not, it's back to the drawing board.

Keep us posted.

But now I wonder if it would be possible to use a bellows blower to create gas-burst agitation in a Jobo tank. With the tank just standing there, would a tube placed down the center, from which bursts of air supplied by a bellows blower, provide an effect agitation? My sense is that the reels might keep the bubbles from displacing the liquid against the film enough.

Rick "who has the tank but has not yet tried any development" Denney

[Brian K]

I use a CPP-2 but do not simply allow the film to spin in the machine. After the first minute of back and forth rotary agitation I take the tank off the machine, use the fat part of my left hand's palm to cover the opening and do several inversion agitations, end over end which lasts about 10-15 seconds and then I put it back on the machine. Another 1'30" and I do it again, etc. The rotation speed is slow to compensate for the added agitation of the inversions. This is the only way i've been able to get perfectly even negatives on the Jobo. I do this with expert tanks and the 2500 series roll film tanks.

Another good method, especially with 8x10 negs are the BTZS tubes. The randomness of the agitation direction combined with rotation works quite well.

The most even 8x10 agitation I ever had was when i had a nitrogen burst system and 3 1/2 gallon tanks. Those negs were perfect every time.

As for the use of a hose and blower bellows, it's not going to provide good agitation using jobo tanks and reels because they simply are not made for that type of agitation and you would need far more pressure, and consistent pressure at that to do a good job.. And I see little benefit from the extra work involved versus just using a Jobo thank on a Jobo machine. You might as well just go with dip and dunk.

The simplest set up with the best results are the BTZ tubes. I think they are being made again, if not, there are plans online for making them out of readily available PVC piping.

[rdenney]

I use a CPP-2 but do not simply allow the film to spin in the machine. After the first minute of back and forth rotary agitation I take the tank off the machine, use the fat part of my left hand's palm to cover the opening and do several inversion agitations, end over end which lasts about 10-15 seconds and then I put it back on the machine. Another 1'30" and I do it again, etc. The rotation speed is slow to compensate for the added agitation of the inversions. This is the only way i've been able to get perfectly even negatives on the Jobo. I do this with expert tanks and the 2500 series roll film tanks.

Brian, that's good to know. I will not use a processor, but will probably construct a manual roller. I would be easy enough to make wheels for the roller that are eccentric, which would cause the random motion provided BTZS tube. I had looked at those tubes, but the space requriements for their use are beyond what I have available. My current house in Virginia does not permit construction of a darkroom as I had in my houses in Texas.

Rick "who will have to experiment" Denney