View Full Version : Jobo Temperature Analysis - end container temp OK for pre-heat? And other questions!

26-Dec-2013, 09:03

Any thoughts appreciated...

I've been doing the jobo main thermostat tweaking that I know is common.
The thermostat is set to 39C which is giving me a dev tank temperature of 38.3.
Tanks were loaded with water at around 35C and given well over an hour to settle.

Temperatures were measured with the following digital thermometer...

See diagram for the areas measured.

Having read a vast number of pages on the forum it would seem that as I am after a dev temp of 37.8 this would be about bang on once the temp has dropped slightly as it is poured in the tank.
Can anyone confirm this?

I've noticed there's quite a variation across the tank from 39.2 in the bath at the dev tank to 37 in the far right container.
Am I ok to pre-heat the tank at 37 or is the variation too much.

I also cross checked the dev tank with the above thermometer, with Paterson Colour and Jobo Colour thermometers, which range from 38.3 to 40.... which one do I trust?

I am developing 5X4 in Rollei C-41.

Thanks all and Merry Christmas from...
A developer with little experience!


26-Dec-2013, 10:34
I use a Paterson thermometer with my CPA. Zero issues for color work. As I'm sure you've read, the most important part of the process is making sure your developer temp is spot on. I've been using Tetenal which specifies 38 degrees. The documentation says you can be +/- 1 degree off. I'd keep it tighter than that if you can (often I've seen people say to keep it within +/- .5 degree). I've found the surrounding bath is usually a bit higher temperature than inside the bottle. In terms of the other temperature measurements across different parts of the processor, I wouldn't worry about it. As long as your temp inside the bottle is exactly where you want it to be, the rest doesn't matter. The drum just needs to hold your developer temperature. It doesn't have to be exact. For bleech/fix, again according to the Tetenal documentation, you can be off +/- 3 degrees. I imagine it's the same for most C41 chemistry kits. In the end, you'll have to run film through the processor and review the negs. When I first started Jobo color work, I did my first batch myself and sent out identical set of negs to my local lab. I noticed my negs were a bit contrasty. It turned out I developed at 3:45 minutes instead of 3:15 (due to a misread of the Tetenal documentation). So, I effectively pushed the negs. The negs will inform how you're doing. Don't expect perfection with your first few runs. Give it some time. Good luck.


26-Dec-2013, 11:01
I monitor the temperature of the trough at the outlet and IIRC Jobo recommends that you monitor it there also. In fact that's where they installed the thermometer holder on my CPA. If the temperature at the outlet is correct, then all the water below in the reservoir must be at least that also and the bottles that are submerged in that water will reach an equilibrium with it. Until that happens the bottles will extract heat from the circulating water which will show up at the trough outlet. Now if the temperature at the trough outlet is X degrees, then the water in the reservoir below must be slightly higher as it will have the tendency to loose heat as it travels the length of the trough which is exposed to the ambient air temperature which is much lower that the C-41 processing temperature and which should be a close approximation of the solution as you pour it into the tank which also slightly cools the solution. So keep the bottle caps closed (you loose heat when you open them) and monitor the temperature at the trough.


Ed Bray
26-Dec-2013, 11:44
The CPE2 shown does not have as good a temperature control as the CPA2/CPP2/CPP3 processors as there is no pumped water system and the water is heated at the bottom of the trough and the convection movement of the lighter warmer water migrates to the top of the trough setting up a non pumped thermal change. Unfortunately this does not lead to high precision and allowances have to be made for the different distances the chemical containers are from the heater. The movement of the drum when rotating influences this further by cooling the water on the external surfaces of the drum when it is out of the water bath.

Sal Santamaura
26-Dec-2013, 12:52
Following on to Ed's post, the addition of a small aquarium pump to circulate water in the bath would be most helpful. Search for numerous Internet threads on the subject to get an idea how one can be added.

26-Dec-2013, 12:58
Or make a simple submerged motor like this to help circulate the water.

26-Dec-2013, 14:07
Thanks for the replies.

A quick update...

I actually bought a tiny (30*40mm approx.) aquarium pump107191
that shifts around 200l per hour, adjustable and on the lowest setting. I've just installed it after taking the first set of temperature readings and it does even things out a reasonable amount. Prob around .3-.4 difference from left to right and a tiny bit more in the open containers but I'm putting that down to fact they flasks sit out of the water and are open to air??
The pump attaches to via suckers between the containers 1&2 (from the left), little bit of a squeeze but it fits.

My first batch of 4X5's are not good at all!
Major colour shift... I don't think the cast is all in the scanning.
Had a read through some other posts but there seem to be many reasons why it may occur... I'm posting the negative in case this gives anyone the opportunity to give a more accurate diagnosis!
Also lots of oddities in the shadows.
Excuse the kami/mylar situation... I need to cut my mylar to size!


26-Dec-2013, 14:41
C-41 is a very forgiving system, with +/-1 or even a bit more degrees are often hard to spot.

I would not rule out the issue with the above posted image is in the scan, It is very common for flatbeds to produce poor scans of low density negatives.
A simple white point correction in Photoshop would answer this question (if you see noise in the black - its scanner a scanner issue).
This though - does not answer any questions as to weather or not the actual processing had any issues as well.
The rollei chems would be the first thing to check. even a full 1 degree variance in C-41 does not really produce a noticeable color shift or density change, most definitely not like the above scan.

To check - contaminated developer (or exhausted) and or bleach time.

27-Dec-2013, 14:56
I've definitely got the scan better but the shadows are still very poor.
Developer wash fresh in a clean/sterilised bottle... however on reading through the forum I extended the bleach time to 6.30... could this be the issue?
Are there any foolproof ways of looking at the negative without scanning to check its quality?

27-Dec-2013, 15:22
What is the bleach supposed to be on the rollei? something like 1.5-2 mins? possibly over bleached but will not produce the issue at hand.

An easy way to have some reference is to look at a known good neg and compare the bases, though that will only tell you if the density is within range, but not much more. After that - a densitometer comparison to a gretag chart.

Still could be bad developer. Start a new batch and a new neg and see what happens.

Good luck

27-Dec-2013, 16:34
Been there, done that!

The most important temperature is the one inside the development tank. Also, using a lift will sure help.
The shift in color in your results seems more like problems with the chemicals. You should buy a roll of control strips and test/tune your processing before develop the important negatives (very cheap on ebay).

I also was interested in improving the temperature control in the CPE, so I taped in a wireless thermometer inside the tank to find the heat transfer function. So after several tests here is what I learned.
Lets call Tr the temperature in the room and Tw the temperature of the water bath measured under the tank.
The curve gets stable pretty quick at Tw-((Tw-Tr)/10). So with the help of Arduino and a couple of sensors I do the E6 and C41 more relaxed than ever.