And that is why I suggested letting a drum spin to splash the water around a bit and reduce the temperature gradient...
Originally Posted by argus
I forgot to mention that in E6 processing it is the bath temperature which is important. So do not measure the temp of the watering bath but, instead, the temperature of the first dev and color dev. Check that you stir a little once in a while to ensure good homogeneity of the solution.
If, then, you check the water bath you'll find it a little on the high side. So put some water at the fisrt dev temp. in the tank and let it roll with a thermometer inside for a couple of minutes (5 to 8 will be excellent as these are the extreme duration for the first dev bath) and then read the temp again in the tank. It should be close if not equal to the correct processing temp (the too hot of the water bath is compensated for by the too low of the air to gain an equilibrium).
When satisfied by the setting, put a nice mark on the knobs in order to be able to get the setting right the next time.
Here, the medical thermometer with it's "hold" capacity is a great help. Of course, this will not work for B&W, but IMHO, B&W is better done by hand in the silence of the lab ;-)
I measure my intemperature of the dev and also when I dump it. Between these two is a difference of about 1½-2°C. So I calculated the intemp a little bit higher to equal. This is working for me.
Release, the best you can do...
This is getting interesting. I have noticed that the water bath temperature is always somewhat higher than the chemistry. In fact it is difficult, at least in my processor, to get the water bath and chemistry to the same point. Even worse, I had assumed that the Expert drum that I use would hold the temperature of the chemistry at the same temperature as the water bath. I will be running tests this weekend to find the temperature differential. Thanks again.
I have an older CPA2, and gosh, is the dial setting off from the actual water temp. When I have my dial set to about 19 C (a bit below the 20C marking on the dial, my water bath temperature as measured by my dial thermometer is 75-77 F (more like 22-23 C). Because of this, I have not ventured to try any C-41 or E-6 at home. This is ok for my black-and-white work, as I have standardized my development times around the temperature gradient and I get consistent, happy results from this. I was contemplating getting a new (or at least only mildly used) CPP2 as an upgrade, but if the CPP2 is as inaccurate, I may as well just do some testing of temperatures until I can nail down what actually is the appropriate temp on my CPA's dial, and just mark the dial.
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When I trim the hihgtemperature (30 - 38°C) settings on the circuitboard of the CPP2 then the low temperature are beneath. If I do it the other way round then the high temperature settings are off. In other words you have to deal with it and always test for the exact grades.
BTW it's normal that the watertemp in de trog is a litle higher - about 1-1½°C) than the chemistry. But this is a constant faktor.
Release, the best you can do...
To "The Flyingcamera",
IIII do E6 at home using the Jobo (it was bought for this use).
Once you've found the setting that gets the chemistry at the correct temp, it's _really_ consistent.
And E6 becomes a matter of half an hour ...
Usually, I prepare the processor with it's chemistry in the various tanks the day above or in the early morning and I turn it on with a timer switch 3 to 4 hours before the planned return to home.
This way, when I have put the film in the tank, the processor is up and ready. Usually, before lunch I've a set of chrome hanging for drying.
A permanent marker or felt tip pen is your friend to mark the settings on the knobs.
My replacement CPE-2 (which I bought on the popular internet auction site) came ready 'calibrated' with a felt tip mark on the dial to show where 20°C ought to be. When I checked it, I found that it's very accurately placed now.
Another innovation that I inherited, and can take no credit for, is a small submersible pond pump. It's very compact, and sits comfortably out of the way in the space beneath the motor housing. The power cable, and a tube of about 4 ft, hang out over the back edge, to which they're taped. How useful, I thought, for emptying most of the water from the unit rather than trying to tip it into the sink when full - with much of it ending up on the kitchen floor. It does do that quite well. But I soon realised its principal purpose, with the tube in the bath, is to circulate the water; which it does superbly well. The result is that it reaches working temperature in minutes and maintains a uniform temperature throughout the process.
I have been advised by the Techs at JOBO that the temperature of the tempering bath is routinely set higher than that indicated to compensate for heat loss at the tank itself. Note that the tank itself is immersed ~ 20% - 30% in the tempering bath, and additionally, there will be cooling when the chemistry is poured from the bottle into the tank itself.
If you are really interested in actual tank solution temperature, be sure that the system is stabilized at a given temperature (one hour should be sufficient), and pour an appropriate amount of water into the tank; let the tank rotate for twenty minutes or so, and *QUICKLY* remove the tank and get a quick responding thermocouple (one of the BD digital fever thermometers might be good) into the tank.
From experience, I have never found processing to be as sensitive to temperature as some would have us believe. I know that tolerances as tight as +/- 1/4 degree F have been specified, but that would take some sophisticated, high end equipment - and even then - I would not be sure of success. Even measuring that accurately would be a problem -Kodak's Lab Thermometer is only "good" for +/- 1/4 degree F - normally the measurement control system should be ten times as accurate as the system control limits - in this case, +/- 0.025F. That would require a laboratory grade thermocouple and a LOT of attention to the heat loss rheology.
I have screwed up - processing film at 35 Degrees C (forgot to reset the JOBO from RA4 color printing) to 38 Degrees C (and vice versa) - 3 degrees C (5 F) "off" - without signifcant color or contrast shifts.
This is all form my experience - the best source of information would be Photo Engineer -- are you there, PE?
Ed Sukach, FFP.
Test Results / Thermometer Calibration, Jobo Processor
Based on suggestions made I checked the calibration of my Kodak Process thermometer against a medical thermometer (the old fashioned max reading type). The two agreed exactly. Then I performed the following tests. each test was done after the Jobo had stabilized at temperature for 2 hours
Jobo Setting: 38°C
Water Bath: 37.2°C
Solutions in bottles: 36.4°C
Solution Temp in 3010 Drum measured with medical thermometer taped to inside: 36.2°C
Based on this I adjusted the Jobo to 39.9°C and got the following results:
Water Bath: 39°C
Solution in Bottles: 38.3°C
Solution in Drum: 38.1°C
The E-6 1st & color developer require 38°C ± .3°C
So there it is. I have my settings. Thanks to all for your help.