This is the first time I have mentioned this on this forum, but generally speaking when using a rotary processing system, you almost always, effectively dilute the developer, compared to conventional developing!
The reason is simple, if you use the Jobo 1520 tank you can develop two rolls of 135 or 120 films. Conventionally you would use 500ml of solution, however for rotary development, you will only use 250ml of solution.
This does have an effect. I bought my Jobo CPE2 in 1988 and I've processed just about anything possible to develop in it. I last used it on the weekend and will use it this weekend; it has had constant use since it was bought.
One of the first things I did was to see if there was much difference between constant rotary agitation and normal inversion agitation by hand. There is, but by my reckoning, not too much.
With colour processing, especially colour neg processing (C41) there is no dilution of the developer and there is no time difference for rotary developing. At the time I was working in a very big commercial colour lab/studio complex. I had access to Kodak C41 test strips and I had someone who could take careful readings using state of the art densitometry equipment. Best of all though, was the fact I could check the filmstrips I processed, with our pair of deep tank C41 processors.
Well there was a difference with my test strips, which is as it should be as I was using fresh chemicals and one shot processing whereas our C41 baths were huge replenishment systems.
The differences were minimal, and I mean minimal. The most important part, colour, was virtually identical. Not quite the same but realistically no difference.
Density was intriguing to the lab technicians; it turned out I was getting more consistent results than the lab. This was due mainly to fresh chemicals for every run.
The deep tank processors would sometimes sit around for 1 or 2 hours then all of a sudden start processing 100 to 300 4x5" sheets as well as about 200 rolls of 120 and the occasional 8x10" sheet, then nothing again until late afternoon when the shooting after lunch would come in.
After in-depth discussions with the Kodak technicians the lab actually bought a Jobo Autolab for processing of special E6 film. This was used in preference to our deep tank E6 processor as it gave more consistent results, especially for density where we would push or pull a 1/3 of a stop. This was only used for special shoots where colour fidelity and density had to be absolutely perfect. The E6 deep tank processor had the same quality issues of the C41 with no film for a few hours then bucket loads. The replenishment systems were always trying to catch up.
The upshot of all of this fiddling was that rotary development gave virtually no different results from a technical point of view with colour.
This made me think about B&W possible differences. So we started a developing test situation using Kodak test strips. We used the lab's roller transport developing (R/T) machine. Which if I remember was a 31cm Colenta E6 machine modified for B&W. The E6 machine was used as it could do a push or pull, which was beneficial for the different B&W times sometimes required in the first bath.
All B&W tests were done with Kodak TMax 100. The reason was that we were a Kodak lab and everything was Kodak.
Test strips done in a corrected bath for the B&W R/T machine each morning after the bath had stabilised.
I then did test strips at home using both inversion and rotary. The common denominator for these tests was that in all cases, the time the film was in the developer was identical. I cannot remember off hand what the time was but if the R/T machine had a developer bath time of 6.5 minutes, then the inversion and rotary times were also 6.5 minutes. All temperatures were 24C, I remember that.
Once again the results were interesting. There was a total of 5 test strips developed over 5 days in each system.
The real interesting bit was that the hand inversion gave the most dense (or developed) negatives. The R/T machine gave very good development and the density was, AFAIK, bang on the money, which pleased the boys in the lab, no end. The rotary developed negatives were just slightly different to the R/T negs in density; they were ever so slightly lighter.
The conclusion we came to, was that there does appear to be a slight increase in developing possibilities when using rotary developing. We believed the reasons the developing was so close to the tightly controlled R/T machine was due to there being less active developing agents able to effect film as the developing solution is diluted by there being less actual developer in a rotary processing tank!
All film test strips were developed in either the R/T machine, which was tightly controlled, or, in my Jobo 1520 two-reel tank.
The 1520 tank for home processing developed one Kodak test strip, one x 36 roll and one x 24 roll on the two reels. The rolls of film had all been exposed to a colour and B&W test chart, for every frame with studio flash in one in session with the same camera/lens and flash.
I developed 4 rolls and 2 test strips in one rotary and one inversion processing session each evening.
Since that time, I have always started with a new film and/or developer and used the manufacturers starting time for the first developing session after having done test exposures of a grey scale and colour chart.
Once I have correct camera exposure and correct developing time established for a film, I can, and do swap between rotary and inversion techniques, without changing my actual developing time. The final outcome is negligible; there is a difference, but not very much.
Mick.
