And now, from Jobo Quarterly, Dead Link Removed the dope on speeds:
What Speed is it Really?
by Ken Owen
Recently a JQ subscriber wrote and asked us to be more specific about processor settings when we write about film and paper processing tests. This is an excellent suggestion we will try to implement in the future. However, it caused me to think that perhaps it might be useful for you, the reader, if I described the various processors and how to "translate" rotation speeds for your machine.
First of all, let me make you aware that you do not need to get too fussy about the precise speeds in use. As a percentage of speed, it appears that an approximately 30% speed shift is required to show a significant difference in the densitometric tests of the resulting images. Years ago, we tested this very concept and found that the 75 rpm speed had to be slowed to about 50 rpm before we showed a 0.03 logD difference in the results. (0.03 logD is roughly equivalent to 1/10th of one ƒ stop.)
Another factor that will affect the speed of the rotation motor is the weight of the load on the motor. A 1526 Combo tank used to process one 8x10 print only needs 50 ml of solution, so there is not much drag on the motor. On the other hand, a 3005 Expert Drum for 8x10" sheet film may contain up to 1500 ml of solution. Plus, the vents on the bottom of the Expert drum draw in water from the processor’s water bath, so there can be a very large drag on the motor when using this drum. For best results, you will need to test your processor speed with the tank or drum loaded with the amount of solution you plan to use in the actual process. On the CPA-2 and CPP-2 manual processors and the ATL-1 AutoLab, this will make a difference in your speed setting. On AutoLab processors from the ATL-2 on up, the speed is microprocessor-controlled regardless of the weight of the drum load, so you don’t have to worry about it.
To test the rotation speed on the CPE-2 (not Plus) CPA-2 or CPP-2, begin by loading the tank/drum with the amount of solution you anticipate using. Then set the speed to the anticipated setting on the dial. Now swing the three-fingered switch out from behind the rotation motor’s magnet or gear. This will allow the motor to rotate in one direction only. (Note: Testing such as this is the only time we currently recommend single direction agitation. For all normal film processing we recommend bi-directional agitation.) Now with the tank/drum rotating, start a stop watch, and begin counting the revolutions by noting the passing of the label with each revolution. After one minute, you’ll know the rotation speed. Obviously you can also count the revolutions for 15 seconds and multiply by 4. But the point is this: it’s easier to determine the rotation speed than it is to take your pulse.
Now let’s get down to the particulars for each processor.
The DuoLab, CPE-2 Plus, ATL-1000 and ATL-1500, as well as the new ATL-500 and ATL-800, all run at a fixed speed of approximately 75 rpm. So there’s no rotation speed adjustments or testing needed here. (DuoLab owners will note that their agitation motor does not reverse direction. When we first saw this we were concerned about the possibility of streaks. However, after testing with BW, C-41 and E-6 films, we found no sign of streaking or bromide drag. We believe this is due to the limitation of small size tanks it is capable of handling. It works perfectly!)
The older CPE-2 processors had two rotation speeds, marked 1 and 2. They were approximately 25 and 65 rpm. There was some variation with individual units, but probably not enough to make any difference in your results. With magnet drive you can use either speed setting, but with the JOBO Lift you must use the #2 setting. The #1 setting doesn’t have enough power to keep on doing the rotation with the additional drag of the Lift arm. At least not for long.
The CPA-2 and CPP-2 have continuously variable speed controls. The dials are marked 0, F, 3, 4, P, 6, 7. Originally the F and P stood for film and paper. But with more research, Jobo learned that almost every process ran better at higher speeds. Today, we recommend as a basic guideline that all tanks or drums that couple to the lower spigot on the Lift arm be rotated at speed P, and that all drums that couple on the upper spigot, be rotated at speed 4. (Those of you running with the magnet coupling will use speed P for all tanks/drums.) These two speeds will be close to 75 and 50 rpm respectively. The single exception to this rule is that Ilfochrome prints should be rotated at speed F (approximately 25 rpm), to help hold down the contrast.
Those of you with AutoLab processors ATL-2 and higher know that you simply select the specific rpm setting you need, without any translation required. On earlier models you could select Quick Start, 25, 50, 75 or 100 rpm, or Disc. The Quick Start was an automatic speed variation program for Ilfochrome. It started out at 100 rpm for the first 25 seconds, and then slowed down to 25 rpm for the rest of the chemical time. For water rinses, it runs at 25 rpm the whole time. The Disc setting was 100 rpm in a single direction. Disc film needed a very high agitation, and reversing directions reduced the agitation somewhat.
Now you are fully armed with virtually all the rotation speed information. If you see any articles written about any JOBO processors that indicate some sort of speed setting, you should be able to convert that to useable information for your machine.
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Since this is freely available on the internet, and not available by other means, I'm posting this as presumed fair use. Moderators feel free to cut back to the link only if that seems more proper. I'm thinking that there's no guarantee that the linked page will remain available in the long term, and the information is often sought out.
Lee
