Jobo Rotation Speed

[Doc W]

Hey, all you Jobonauts. What is the effect of the speed of drum rotation on development? I am talking specifically about b&w. The recommended speed for b&w is 50 RPM. Will a slower speed (25) increase development time? Will it lower contrast? What about a higher speed (75)? The slower speed will put the film in contact with the develop less than a faster speed but... I can't quite my head around the relationship between speed/dev time/contrast. Help me out!

 

[DREW WILEY]

Depends on the specific process and chemistry. In my opinion, even the lowest setting on a Jobo is too fast for some things. They need a stronger gearmotor with a lower speed range option. Allegedly, some of the newest ones have been improved in this respect.

 

[Sirius Glass]

I use the 'P' speed for the 130 and 135 tanks. And '4' for the Expert Drums and print drums.

 

[Vaughn]

I use the 3005 and 3006 drums on a Unicolor motorized roller base. Between 15 and 16 RPMs (just measured tonight developing 8 sheets of 8x10).

If aggitation is constant, then I think the speed of agitation is not as significant. The speed of chemical reactions on the surface of the film would be constant if fresh chemicals are always being introduced to the film surface. Temperature and dilution would have greater affects.

 

[Neal]

Dear DocW,

In my experience with 25XX tanks it doesn't matter. My drive is homebuilt. Originally it ran at 48rpm in one direction but when I upgraded the motor so it would reverse I went with 72rpm. No difference.

Good luck,

Neal Wydra

 

[RalphLambrecht]

Hey, all you Jobonauts. What is the effect of the speed of drum rotation on development? I am talking specifically about b&w. The recommended speed for b&w is 50 RPM. Will a slower speed (25) increase development time? Will it lower contrast? What about a higher speed (75)? The slower speed will put the film in contact with the develop less than a faster speed but... I can't quite my head around the relationship between speed/dev time/contrast. Help me out!

I tested for this numerous times;never found a difference in contrast or required dev time.Now,I just use the slower speed in hope that the is the least strain on the motor.

 

[Sal Santamaura]

I use the 'P' speed for the 130 and 135 tanks. And '4' for the Expert Drums and print drums.

There is apparently no limit to the number of times I must point out how meaningless statements like that are. Without knowing the serial number of one's processor, there is no correlation between dial settings and actual rotation speed.

Here are the facts, once again. I transcribed the following from a printed copy of a Web page Jobo no longer makes available.

How do I properly set the rotation speed for my CPA-2 or CPP-2 processor?

For many years, JOBO has recommended rotation speed settings of 4 for use with our 3000 series drums and P for all other tanks and drums, to properly set the rotation speed. Now there are two different sets of speeds which need to be listed based on the type of motor in use in the processor. The following processors need to follow the new speed settings.

• All CPA/CPP processors with serial numbers greater than 22000.
  
• All CPA/CPP processors that have been upgraded with the new rotation motors (93026).

Both of these categories can most easily be identified by the screw head in the center of the cog on the rotation motor shaft. If there is a hex-socket screw (it uses an Allen key to turn the screw in installation) then it is the new style motor.

All older motors, using a slotted screw in the center of the cog on the motor shaft, still use the old speed settings shown below, and as listed in the instruction manuals that accompanied them.

Old Settings
0 - Off
F - 25 r.p.m.
3 - 40 r.p.m.
4 - 50 r.p.m.
P - 75 r.p.m.
6 - 78 r.p.m.
7 - 80 r.p.m.
*New Settings
0+ 25 r.p.m.
F - 46 r.p.m.
3 - 70 r.p.m.
4 - 86 r.p.m.
P - 86 r.p.m.
6 - 86 r.p.m.
7 - 86 r.p.m.​

*These speeds are approximate and variations of 10-15 r.p.m. will not show up in your processing results

If you want to determine the proper speed settings for your processor, put a drum on the processor filled with an appropriate amount of water to simulate normal processing loads. Then swing the three-fingered switch out of the way, so the drum will only rotate in one direction, and then begin timing and counting the rotations of the drum. (Only use the single direction rotation for determining the correct speed dial settings. Always use bi-directional rotation when processing film or paper.)
​

This was published by the old Michigan-based Jobo USA folks. Enjoy.

 

[Doc W]

I should have given more detail. I am using Expert Drums in an ATL-3. It has rotation speeds of 100, 75, 50, and 25. I have been using 50 for b&w processing.

 

[Raphael]

Hi Doc,

New at Jobo machine ?
With my older ATL1, I'm used to the "P" Speed, but found the neg' rather on the contrasty side. So now, I'm not using higher than 4, but I can't swear it actually changing something, without objective contrast measures...

Best regards,

Raphael