If spindle agitation produces density differences front to back...

[Arvee]

why doesn't Jobo's rotating processor behave the same? It's still the same type of rotation just displaced 90 deg. in axis of rotation.

 

[NB23]

As far as I’m concerned, 90 degrees is the complete opposite (180 degrees would be back to square 1), therefore the liquid’s gravity push downwards onto the emulsion as it is rotating, as opposed to none when the tank is in the upright position, does the trick.

 

[MattKing]

The liquid tumbles in the tank turned on its side.
A vertical tank plus a turning spindle results in the film just sliding through the liquid, leading to much less potential randomization of the liquid.

 

[koraks]

why doesn't Jobo's rotating processor behave the same?

A Jobo isn't necessarily entirely free of uneven development, but it depends on reel geometry and rotation speed. It's actually quite common in certain film formats (IMO especially 120 and 4x5") to see areas where flow was more laminar instead of turbulent, causing reduced density. This shows up as 'wagon ruts' (Google for it; you'll find some threads about it on e.g. LFPF) or flow marks especially along the edges of the film where it touches the reel.

Conversely, twizzle stick agitation isn't necessarily as problematic is touted by some; in many cases it yields good evenness, especially on 35mm film.

 

[AgX]

As far as I’m concerned, 90 degrees is the complete opposite (180 degrees would be back to square 1), therefore the liquid’s gravity push downwards onto the emulsion as it is rotating, as opposed to none when the tank is in the upright position, does the trick.

Fluid pressure forces act in all directions. Thus lateral as vertical.

Also pressure does not matter anyway.

 

[Arvee]

[QUOTE="Conversely, twizzle stick agitation isn't necessarily as problematic is touted by some; in many cases it yields good evenness, especially on 35mm film.[/QUOTE]

In practice I find this to be true; however, I usually do short (12+ exp.) rolls with the film residing in outer tracks, never in the center. I've never had an issue with uneven development.

 

[Nicholas Lindan]

You have to twizzle the stick randomly and quickly - the aim is to create turbulence in the developer.

A Jobo is only partially filled with developer -- the film dips into the developer, which doesn't rotate with the tank, then lifts out of the developer, drains and enters the developer again. This assures a good flow of developer over the film.

 

[AgX]

A Jobo is only partially filled with developer -- the film dips into the developer, which doesn't rotate with the tank, then lifts out of the developer, drains and enters the developer again. This assures a good flow of developer over the film.

Depends what you define as "Jobo".
Some here only relate Jobo tanks with rotational developing. Though parts of their tanks were designed with inversion processing in mind, some models even included stick-agitation.

 

[Arvee]

Thanks for all the comments; agitation schemes are a mysterious and somewhat misunderstood topic.

I think I'm going to try and emulate the Jobo's agitation action manually with my Paterson SS4. Having never seen a Jobo in operation in person, can a Jobo owner please describe the machines sequence, i.e., time/direction of rotation and any other motions beyond simple alternating rotation?

 

[pentaxuser]

Thanks for all the comments; agitation schemes are a mysterious and somewhat misunderstood topic.

I think I'm going to try and emulate the Jobo's agitation action manually with my Paterson SS4. Having never seen a Jobo in operation in person, can a Jobo owner please describe the machines sequence, i.e., time/direction of rotation and any other motions beyond simple alternating rotation?

I can't say what my alternating rotation cycle is but I think it changes direction every 3 seconds It doesn't do any other motions that I have ever observed

pentaxuser

 

[koraks]

time/direction of rotation and any other motions beyond simple alternating rotation?

Clockwise for about 1.25 rotations and then it switches direction. My CPE2 has 2 speed settings; low speed is something like 30rpm, high speed maybe 80 or so, idk. No other motions except cw/ccw.

agitation schemes are a mysterious and somewhat misunderstood topic.

By whom?

 

[Arvee]

Thanks, everyone, I will replicate that sequence.

 

[AgX]

Can a Jobo owner please describe the machines sequence, i.e., time/direction of rotation and any other motions beyond simple alternating rotation?

My CPE2 has 2 speed settings; low speed is something like 30rpm, high speed maybe 80 or so, idk.
No other motions except cw/ccw.

Depending on Jobo tank model employed on a non-Lift Jobo processor it yields a vertical swivel movement pivoted at the coupling.

 

[koraks]

I can't vouch for other types but my non-lift CPE2 only rotates; no other movements whatsoever. Indeed, there is no mechanical provision for anything except rotation.

 

[AgX]

As I said, it depends on model of Jobo tank. Some models yield swivelling.

But you may modify yours to similar effect.

 

[MattKing]

My Beseler roller agitator works similarly to the description above for the JOBO:
I actually have gone away from rotary agitation for anything but the first 30 seconds of the development stage, because I often load two rolls of 120 on an AP/Paterson reel, and rotary agitation during the development stage leads to the two rolls moving back and forth within the reels, and often overlapping.
The film doesn't wander that way if rotary agitation is used for the other steps (pre-rinse, stop bath, fixer, HCA).
The roller agitator works with the Paterson Super System 4 thanks that hold one litre of liquid - just add one heavy rubber band near the bottom.

 

[AgX]

I often load two rolls of 120 on an AP/Paterson reel, and rotary agitation during the development stage leads to the two rolls moving back and forth within the reels, and often overlapping.
The film doesn't wander that way if rotary agitation is used for the other steps (pre-rinse, stop bath, fixer, HCA).

Any explanations?

 

[MattKing]

I know that film in developer is quite slippery - probably more slippery than in water alone or any of the other chemicals - at least in plastic reels.
I have no better guess.
But since I started doing this way, I've never had a problem with overlap. And that is with a lot of rolls of film.

 

[AgX]

Yes, it could be the alkalinity of the developer bath. Interesting aspect.

 

[Sirius Glass]

I can't vouch for other types but my non-lift CPE2 only rotates; no other movements whatsoever. Indeed, there is no mechanical provision for anything except rotation.

I have the CPP2 with the lift and the only movements are the rotations and the lift and then end of each chemical. The filling is done in the horizontal position.

 

[Moose22]

I actually started with a non-patterson tank. The one sold as Omega or AP. I switched to patterson because the omega tank leaked too much sometimes through this rubber gasket it has under the lid. Before I got the patterson I never quite got what this issue using the rotary agitator was for people.

The Omega has a different thing with the swizzle stick. There are ribs on the bottom of the tank and the center column's base is wavy. So when you rotate it it also goes up and down. I did a little experimenting and was never able to get it to show any issues even without inverting it for agitation.

It is a small thing, but the patterson eventually does get to the point where the fluid is all moving at the same speed as the film. They tried to solve that problem with the Omega and were quite clever.

 

[koraks]

As I said, it depends on model of Jobo tank. Some models yield swivelling.

But you may modify yours to similar effect.

An eccentric spindle of some sort I presume? Do you have a link to an example?

 

[AgX]

An eccentric spindle of some sort I presume?

No, a eccentric ring mounted around the tanks.

 

[AgX]

The Omega has a different thing with the swizzle stick. There are ribs on the bottom of the tank and the center column's base is wavy. So when you rotate it it also goes up and down.

Similar is found at some Jobo tanks. However the lift is very small. And there is a wedge/ratchet effect. So I assume in these cases the idea is just to direct the twirling of the stem with the reels into one direction, so that the spiral's opening can shovel-in so to say the fluid.

 

[Sirius Glass]

One important part is that, as advised by Kodak, develop for times longer than five minutes. That means some times we have to chill the chemistry first.