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  1. #1

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    C-41 film processing image quality and absolute temperature

    In light of recent discussions on APUG about the accuracy and precision or otherwise of various methods of measuring the temperature of processing solutions, I have a question concerning C-41 processing, namely, how important is the accuracy of the absolute temperature to maintaining image quality?

    If I recall correctly the C-41 process is supposed to run at 38.7ºC in my Jobo ATL-2300. Assuming correct mixing and activity of processing solutions, if the real temperature of the solutions was 37.7ºC or 39.7ºC, would this adversely or materially affect image quality, grain, sharpness, or anything else?

    Tom

  2. #2
    hrst's Avatar
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    37,7C rather than 38,7 :-).

    The biggest effect is that you will get a pull or push process; wrong contrast and colour mismatch (crossover). Too high temperature increases contrast and too low decreases it. Color layers don't react exactly similarly to the variations, which causes contrast mismatches. If you scan your negs, this doesn't probably mean anything as it is fixed in levels or curves tool.

    However, I tend to think that these problems are fairly small; especially, if you scan, then the processing temperature and time doesn't play so big role. If you print your negs, current RA-4 papers tend to be quite high in contrast so you don't probably want to overdevelop but rather err to the underdevelop.

    But, 1C deviation IS quite big. I would say that 0.5C is okay for me, some people would want 0.2C precision.
    Last edited by hrst; 10-24-2009 at 04:28 PM. Click to view previous post history.

  3. #3

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    Quote Originally Posted by hrst View Post
    But, 1C deviation IS quite big. I would say that 0.5C is okay for me, some people would want 0.2C precision.
    I agree, my post is in the context of what is accurate... As you're probably aware the ATL-2300 is automated so the film (for example) does get 3 minutes 15 seconds development each time. I use the Fujihunt 5 litre C-41 Xpress kit.

    Tom

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    tiberiustibz's Avatar
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    I'm told that it takes 5 degrees F to cause crossover. I think a degree F either way will not hurt your cause that much. I don't think my processing is that accurate but I get very good results nevertheless. The assumption is in heat transfer between the water bath to the cylinder. It's very easy to keep a tub of water very close to a temperature, but very hard to know what temperature to use. I know it's somewhere between 100.5 and 102 degrees F, and I know it changes based on how much water is in the bath (ie, how much of the metal tank is covered.) For now I pour in at 102, and keep the water bath 101 to 102 and pray. Seems to be working.

  5. #5
    Photo Engineer's Avatar
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    You stand the risk of getting color balance shifts and contrast changes in the film if you move too far, but there is some leeway built in. The standards we used were +/- 0.15 degree C for "perfect results" centered on 37.8 deg C. or, +/- 1/4 deg F centered on 100 F.

    I have 2 Kodak process control thermometers that are nearly 1 foot long and use mercury. They are in stainless steel jackets and last I looked were pretty expensive. They match, but differ from most every other thermometer I own, dial or liquid. I have at least 6 thermometers.

    The interesting thing is this. If you are off by a degree and repeat that over and over, you will at least get consistant results. That is, if you are within 1/4 degree F of your own center point.

    This gets back to the old thread here though, if you have one thermometer, you know the temperature, but if you have two, you are not so sure anymore.

    PE

  6. #6
    tiberiustibz's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    This gets back to the old thread here though, if you have one thermometer, you know the temperature, but if you have two, you are not so sure anymore.

    PE
    I once processed with a thermometer that was 6 degrees cold. I knew the temperature was correct though...

  7. #7
    Ed Sukach's Avatar
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    From experience...

    I have processed C41 film in a JOBO CPP-2 inadvertantly set (not reset from RA-4 development) at 35 Celsius - -3 degrees C from the required 38 C; similarly, I have processed RA4 paper at 38 C - +3 high.
    In neither case was the color balance or contrast, or anything else that I could notice, significantly enough "off" to cause any sort of unusual problem in printing.

    IMHO, it is very nearly impossible to control any process likely to be used in anything but an ultra-sophisticated Industrial Lab / Production facility to anything closer than +/- 1 degree F... and even so, we continue to produce consitently high (and I mean HIGH!!) quality images.
    Carpe erratum!!

    Ed Sukach, FFP.

  8. #8
    Photo Engineer's Avatar
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    Ed;

    To be fair, the paper is less temperature sensitive than the film, so your results in that regard are to be expected.

    PE

  9. #9
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    When I was processing C41 with a kit using, I used the alternative times it gave for 31c, as it was much easier to keep a consistent temperature, in fact, ambient in summer for sitting water is around 25-26 so it doesnt drop, unlike ~38, which was great.

  10. #10

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    It depends on the type of film, maybe also on the type of chemicals. Some films are very forgiving, others react very sensitive to changes in processing conditions. In some cases, a slight deviation from "standard" might gain better results. The fact that c-41 is an "industry standard" does not mean that all combinations of film and chemicals produce their best results exactly at standard conditions.
    Small-scale home processing is never 100% equivalent to processing in a commercial c-41 machine, so one has to make fine adjustments anyway.
    And: although there is always the obvious "I processed 5 degrees off and had perfect results"-posting, such findings are .... exceptional. Plusminus 0,5 degrees celsius and plusminus 5 seconds should be easily obtained in a home darkroom. Remember that 0,5 degrees celsius (very roughly) equal about 15 sec in processing time.
    I guess the biggest variable in C41 home processing is the uncontrolled aging of the developer.

    Georg

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