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  1. #1
    justin parker's Avatar
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    C-41 test strips giving low HD values and other issues

    I have recently acquired a Photo Therm Sidekick for personal use, and I want to get reliable and repeatable C-41 results from it. To that end I bought myself a X-rite 810 off of eBay and today the transmission calibration standard I ordered from X-Rite arrived so I calibrated the densitometer (hopefully) and ran 4 35mm reels in the 4 reel tank for the Sidekick with a Kodak C-41 test strip on each reel. I am using Kodak Flexicolor SM chemicals. I ran 4 actual rolls of C-41 through it yesterday and scanned them on my HR-500+ scanner and the negatives scanned just fine. But still... I wanted to verify that my process was within tolerance. Unless I am doing my math incorrectly, I am WAY out of tolerance. So now I am quite confused where to start.

    Patch
    Channel Reference Strip
    + Correction Factors
    Test Strip
    Yellow Blue 2.91 2.72
    D-max Blue 3.00 2.81
    HD Red 1.35 0.89
    '' Green 1.78 1.35
    '' Blue 2.25 1.90
    LD Red 0.56 0.52
    '' Green 1.00 0.89
    '' Blue 1.30 1.28
    Dmin Red 0.22 0.40
    '' Green 0.63 0.83
    '' Blue 1.00 0.97

    Basically only the blue readings are remotely correct. My HD values appear to be way out of whack. The test strips have been cold stored in my fridge and the canister was just opened this morning. I notice now the expiration date was in 2012 ... that can't explain this hugely errant test strip result can it? I checked and adjusted the bath temperature to heat to 100.0°F using a digital fever thermometer as well as a dial thermometer for color darkroom processing.

  2. #2

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    Dear Justin.

    If your negatives scan well, and the color balance is OK (Do you had a close look to the grey-tones? Is there a color crossover somewhere? What about shadow regions, is visible Information detectable, ... I do presume so, the LD densities which indicate film speed are OK) I would suspect the reference strips beyond expiration date. In the end this is just a piece of (very accurate) exposed Film, and the latent image will suffer over time…

    Next suspicion would be wrong calibration or wrong filters (status M?) of the densitometer, or a mixing Error of the chemicals, or contaminated developer. But as dramatic as it looks on your examined / measured strips you would clearly recognize faults in the scan too. This would be a weird combination of Red-Cyan and Green-Magenta color crossover over the greytablet…

    Here is a link to Kodak's Process monitoring and troubleshooting guide
    http://www.photolabs.ru/manualc41.pdf

    Regards Stefan

  3. #3
    markbarendt's Avatar
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    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  4. #4
    justin parker's Avatar
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    Slightly better results with second run...

    Thanks guys for your helpful responses. I do have the Z131 manual but my initial test strips were so far off the mark that I didn't know where to begin. I ran a new run this morning with fresh developer and I got better, but still not in process control, results. The only other thing that went differently yesterday was that with the Sidekick it does a pre-soak with tempered water and the machine had an error loading the developer to heat and so the pre-soak went on for several additional minutes. I know Photo Engineer advocates a pre-soak in rotary processors, but I don't know if PE has ever mentioned whether an excessive pre-soak could cause issues.

    The new numbers I got today, after doing the math to get values-aim are:

    Parameter Channel Value-Aim
    Dmax-Y B -0.02
    HD-LD R -0.07
    '' G -0.02
    '' B -0.12
    LD R -0.02
    '' G -0.08
    '' B 0.05
    Dmin R 0.00
    '' G 0.00
    '' B -0.01

    I have also ordered fresh control strips from Minilab/Liberty Photo but those might not come till next Wednesday since apparently they ship them on ice on Mondays.

  5. #5

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    One thing that might be worth checking is the temperature you are processing at and it's consistency. A medical-thermometer and a bi-metallic strip thermometer are rather sub-optimal for process control. Find yourself a calibrated darkroom thermometer and set up the machine using that at each stage. It may help I think?

    Where it is possible to compare the pH of the developer to the figure provided by Kodak, then of course do that too.

  6. #6

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    Dear Justin.

    The new control strip looks definatly better, the strange red values are OK now. If you do a wet prewash you will easily find some differences in the densitometers reading. This may be the reason for the differences in your blue readings, next to expired test strips. For my personal use I’ve abandoned a wet prewash in C41/homebrew for exact this reason. Have you printed the Negatives of the new run? Suppose they look pretty fine…

    Regards stefan

  7. #7
    justin parker's Avatar
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    Quote Originally Posted by MartinP View Post
    One thing that might be worth checking is the temperature you are processing at and it's consistency. A medical-thermometer and a bi-metallic strip thermometer are rather sub-optimal for process control. Find yourself a calibrated darkroom thermometer and set up the machine using that at each stage. It may help I think?

    Where it is possible to compare the pH of the developer to the figure provided by Kodak, then of course do that too.
    Yeah I might look into borrowing equipment to compare pH but since it is the Flexicolor SM and you just mix from concentrate I am pretty sure I have mixed it correctly. No starter or replenisher involved. It is possible though that the freshness between developer mixed a week ago and freshly mixed mattered, but I sure hope it wouldn't cause things to be that far out of tolerance when stored in Jobo bottles.

    I can check the temperature of the tank the Sidekick uses to heat the chemical up before loading into the drum. When I calibrated it to 100°F (by adjusting a potentiometer on the circuit board) I used both a digital fever thermometer, a metal darkroom thermometer and a glass color darkroom thermometer I have. They all seemed in good agreement.

    The two main things I can vary in my process are the developer time (currently set to 3:15 on the machine, and I think timed from when the chemical starts loading to when it thinks it will be done draining) and the temperature.

    The Sidekick, since it doesn't have a tempered water bath to spin the drum in, uses a combined of a presoak with tempered water and hot air blowing on the drum to warm up the film and drum before putting the chemicals in. The drum itself has a temperature sensor on it that it uses to maintain the temperature. (It doesn't seem that one needs to be calibrated unlike the heating tank.)

    I got them to overnight my new test strips to me so I will start again tomorrow. I will try and check to make sure the drum is being well drained during each step so that there is no carry over over the pre-soak water into the developer, and developer into bleach etc. And then if I am still out of spec I will try adding some time to the development (after double checking the temperature is indeed 100°F)...



 

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