That’s right, agitation should be turbulent and random. This is gentle and consistent. I think even when the film dips, the rotation is so smooth that the laminar layer isn’t disturbed.
@Andrew O'Neill is right about Bromide Drag. This case is the flow of fresh developer into an adjacent area accelerating development.
Bromide slows development, as is well known based on how many comments in this thread point out.
The classic reason is no agitation (stand) and a textbook example is white billboard type on a gray background. The gray background would print with dark streaks.
View attachment 346748
Thank you for your input Bill.
I think your previous diagnosis could certainly be the case but...if agitation should be 'turbulent and random' where does that leave the Jobo rotary process?
Please excuse me if I am wrong but i think the Rodinax and Jobo tanks work on the same principle.
First question that sprung to my mind as well as the fact that we have a number of members here using Jobo rotary processors with success. Finally that leaves the question of why it doesn't give the same problem with C41 films
Is the speed of Rondinax agitation not enough compared to Jobo assuming that Bill is saying that there is a critical speed beyond which rotation gives enough turbulence I note that my Jobo reverses the direction of rotation every 3 secs which has to be pretty turbulent. What's the action of a Rondinax/Lab box tank?
I look forward to Bill's answers on this
pentaxuser
The action of the Rondinax is in one direction only. I believe that there are some Jobo tanks that same ie: not bi-directional. Obviously, being manual, the rpm can be whatever one wants it to be within reason. An earlier poster settled on 40rpm with success. I'm not sure how he measured the speed but I am certainly in that region. The Agfa Rodinax manual recommends 1/2 turn with a slight jerking movement every two seconds for what its worth. I presume the jerking movement is to dislodge/dissipate any spent developer.
(not Bill, but I will inject this and leave it alone after this)
These all fall under the category of "directional effects" which can entail both bromide drag and other processing defects whereby either a uniform movement of developer flows over a negative without disruption (even with rotation in a bath) or developer byproducts "flow" from an area of high density toward an area of low to no density (as in stand developing).
Rotation in one direction without reversing creates laminar flow issues.
Stand developing creates issues of more energy/movement over dense areas, with the accompanying "fall" of exhaused byproducts of development toward the bottom of the tank over whatever lies below the dense areas.
That's why as a GENERAL rule randomized agitation is preferred over just rotation or a linear motion through a developer bath for consistent overall development. As with any general rule, there are exceptions and instances where this is not a problem with typical exposures.
Faults with the the above means of agitation or lack thereof, only appear under certain circumstances.
Anyway, I am done.
The former is the case but the latter not.To get drag the film must be vertical in the tank and there must be no agitation.
Thank you for your input Bill.
I think your previous diagnosis could certainly be the case but...if agitation should be 'turbulent and random' where does that leave the Jobo rotary process?
Please excuse me if I am wrong but i think the Rodinax and Jobo tanks work on the same principle. If the laminar layer isn't disturbed surely that would invite inconsistencies on a regular basis? Or am I missing something?
The Jobo tanks have very fast moving fluid over all parts of the film even when running at slower speeds. The moving reel in the roll film tanks create a lot of turbulence and must lift a lot of developer as the reel exits the developer when it turns. I haven't used the type of processor you are using so I may have the workings wrong in my head, but it sounds like the film itself is just smoothly flowing through the developer and remaining out of the liquid for long stretches of time, especially the ends of the roll. That's significantly different from the Jobo where the used local developer is quickly mixed back in, or manual tanks where the film remains under the developer the whole time and diffusion can help as long as agitation isn't too infrequent.
If Bill's explanation is correct, and it sounds likely to me, then a faster movement through the machine should significantly minimize the issue. This would be most important early in the development since that's when the bulk of it takes place.
The film is not out of the developer for long periods of time. Agfa ( the makers of the Rondinax) specify 1/2 a turn every two seconds. So the film is only out of the developer for two seconds (or less, if one decides to rotate faster) at any one time.
As previously mentioned the turns should be of a jerky nature. This I presume is to break up the laminar flow. So, if I am not mistaken the process is not too dissimilar to the Jobo.
Theoretically, if this is indeed the problem then yes, a faster speed and more forceful approach should take care if it. The only concern with this is how the negs will appear aesthetically in regards to increased contrast (which can be adjusted by time obviously) and increased grain. Apart from these recent anomalies I have
honed the whole process to consistently produce very nice and easy to print negatives.
I should have searched first for the Rondinax as it is not working the way I thought understood it. It actually does look very similar to the Jobo reels in operation, but it appears to only rotate in one direction. Is that correct? If so that could be significant.
Yes that is correct. See post #79.
Are all Jobo tanks bi-directional?
Yes that is correct. See post #79.
Are all Jobo tanks bi-directional?
This is a great discussion, but would be much better actually talking. Zoom, anyone?So George, you can get bromide drag with continuous agitation and if the streaks are bromide drag then is Andrew O'Neill point nonsense His point was this "Actually, I just realised that you are showing us the positives. The drag marks are lighter. Bromide drag marks should be darker in the positive (clear in the negative).
Chuckroast can you say why pre-soaking may cure the problem when the OP has never used this and has never suffered this problem before?
Something or things has.have changed but previous success would suggest that unless he has been very lucky in the past and his "winning streak" has stopped it is unlikely to be either
pentaxuser
My understanding, based purely on the range of opinions expressed is that there is no understanding of what constitutes insufficient turbulence. Is what we call unidirectional agitation known to be a problem? Has there ever been anything resembling a scientific experiment on this? Does anyone know if rotation in one direction really results in insufficient turbulence. You'd need a transparent tank to see, wouldn't you? If the tank turning in one direction only "slices through the film" without creating any motion or only a uniform motion and therein lies the problem then when this ends and the tank reverses why does the film then experience any turbulence if there was none before? So is even a Jobo processor the right thing to use?pentaxuser - My understanding of bromide drag is that it results from unidirectional agitation, not continuous.
My understanding, based purely on the range of opinions expressed is that there is no understanding of what constitutes insufficient turbulence. Is what we call unidirectional agitation known to be a problem? Has there ever been anything resembling a scientific experiment on this? Does anyone know if rotation in one direction really results in insufficient turbulence. You'd need a transparent tank to see, wouldn't you? If the tank turning in one direction only "slices through the film" without creating any motion or only a uniform motion and therein lies the problem then when this ends and the tank reverses why does the film then experience any turbulence if there was none before? So is even a Jobo processor the right thing to use?
What is clear is that the OP's Rondinax/Lab box tank has a jerk built into to its motion so this would suggest that as a cause of his problem of what may or may not be bromide drag due to lack of developer motion this may be low on the list of likely suspects or so it seems to me
pentaxuser
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