Accurate thermometer for C41

Discussion in 'Color: Film, Paper, and Chemistry' started by osprey48, Mar 20, 2012.

  1. osprey48

    osprey48 Member

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    What kind of thermometers do you use to process colour films? I've heard that the usual spirit ones I use for B&W are not accurate enough. Or are they?
    Does anyone use cheap kitchen food temperature probes? Or are they worse? Or doesn't it make any difference?
    Any info much appreciated.
     
  2. jscott

    jscott Member

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    My choice for all darkroom applications is an instant read infrared beam model with digital readout. It's a gun-like gadget. Just aim it into your chemicals. Very accurate, fast, and easy.
     
  3. Gerald C Koch

    Gerald C Koch Member

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    What type of thermometer you use is not important. What is important is that it be calibrated with another thermometer that you can trust. For this purpose I use two mercury filled lab grade thermometers with a range of -10 to 100 C.
     
  4. tnabbott

    tnabbott Member

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    According to one maker's website: a backlit LCD shows temperature readings, and the thermometer has a range of -58° F-1,022° F--twice the breadth of typical infrared thermometers--and an accuracy within ±3.6° F.

    In other words, completely useless for home development...
     
  5. perkeleellinen

    perkeleellinen Member

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    I use a Jobo 3321 which I was lucky to find on ebay cheap. Its scale is down to 0.2C and I think it's possible to read down to 0.1C
     
  6. ras351

    ras351 Member

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    I have a Kaiser precision thermometer. It has an expanded scale which makes it fairly easy to read to around 0.1C. Whether or not it's accurate is another question but providing it's consistent and my process is tuned for it, it's not a problem.
     
  7. Lamar

    Lamar Member

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    I use cheap kitchen thermometers. I check them before use against a medical thermometer and apply any correction. Never had any problems……
     
  8. perkeleellinen

    perkeleellinen Member

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    A question for those of you using household thermometers for C41: how do you hold the developer to +/- 0.15C? Household thermometers I've seen are usually +/- 1C. Have those of you with less accurate thermometers found these tolerances are unnecessarily tight?
     
  9. DREW WILEY

    DREW WILEY Member

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    Kodak process thermometer. They've always been expensive but sometimes turn up used at reasonable prices. Don't confuse this with cheaper Kodak thermometers. Equivalent units can be obtained from scientific supply houses. Expect to pay at least a couple hundred bucks new.
     
  10. DREW WILEY

    DREW WILEY Member

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    Maintaining correct temp can be done in a large water jacket in reasonable temp for "drift-by" technique. But a lab grade recirculating thermoregulator is the best way. For years I used a CPI
    Accutemp, which would easily keep water temps within a tenth F. When it finally burnt out I found
    something that cost almost a grand and is less convenient, so only use it only for really fussy work like color separation negatives. Thermostatic mixing valves aren't particularly good for critical use.
     
  11. nworth

    nworth Subscriber

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    The Kodak literature makes a point about the thermometer being accurate to 1/4 degree F. My experience is that that is overkill for most work, and about 1 degree works for the average user. Most of the dial thermometers sold for color work are well within this tolerance.
     
  12. perkeleellinen

    perkeleellinen Member

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    Does this apply to both scanning and printing?

    I ask as I print my negs and I'm concerned by allowing temp to deviate by one degree I'll have a nightmare trying to balance colour.
     
  13. osprey48

    osprey48 Member

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    Thanks for the info. Firstcall photographic do a digital probe type for about £12, which is all I'd want to pay anyway, so I'll test it against my spirit one.According to what I've been reading about C41, a half or even 1 degree variation isn't that disastrous for an amateur hobbyist like me anyway, so I'll give it a go and adjust my times and temps as I get more experience.
     
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  15. John Shriver

    John Shriver Member

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    I calibrate a 3 inch Weston Miroband against a Kodak Process Thermometer Type 3. The Kodak thermometer is great, but too fragile for everyday use. (Nor do you really want to break a mercury thermometer in today's environmentally conscious world.) Now, I only do B&W with it right now, although I did do one roll of C-22.
     
  16. madgardener

    madgardener Member

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    I use an instant read food thermometer that I got at a restaurant supply house. Its good to .1F and they adjusted and calibrated it for me. It cost me $20. For my water bath, I use a standard probe thermometer, $10 at IKEA.
     
  17. Mike Wilde

    Mike Wilde Member

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    My reference thermometer is a scientific type mercury thermometer in plastic coated glass. I picked it up at a liqidation auction with about 10 other (some broken) thermometers for about $20. It is about 2' long and goes from -10 to 100F in easily read half degree increments. It comes out perhaps once per month to fine tune or verify offsets for the other more pedestrian themometers in my different process equipment.
     
  18. Lamar

    Lamar Member

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    I know there are some tolerance issues but I have seen no problems resulting from using these thermometers. I do small tank developing with the associated inherent inaccuracies. Varying elapsed time to pour developer out of the tank between two rolls and one roll, varying time to get the bleach in the tank, change in temperature when agitating outside the bath, etc....... This is a hobby for me. I try to be as accurate as I can but I don't use densitometers to check results. From a visual standpoint I see no problems in my film that I can attribute to thermometer issues. I check against a medical thermometer and apply the correction then enjoy the process and results. You can check out some of my results here.

    http://www.lamarlamb.com/On-Film



     
  19. Tony-S

    Tony-S Member

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    OK, so is there a link to a thermometer that is relatively inexpensive and calibrated out of the box?
     
  20. benjiboy

    benjiboy Subscriber

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    Patterson certified mercury colour thermometer, they are guaranteed to be accurate to + or- 0.3 degrees C. straight out of the box.
     
    Last edited by a moderator: May 4, 2012
  21. hrst

    hrst Member

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    There is one type of a cheap "household" thermometer that meters just perfectly at 100F/37.8C, because they are designed just for that close range and calibrated to high precision; if they were not, people would notice that soon in their intended use. They can be mercury type or, most usually today, digital. The digital ones are usually waterproof, too.

    You have to guess what it is. You probably have one.

    I have compared three of those, from different decades, and found they were all +/- 0.05 deg C compared to each other. Yes, 0.05, not 0.5.

    And, usually people have experience in using those so you will know it will show at least about correctly, without depending on any "certified by company X that makes most of its profit by selling low-quality overpriced plastic jugs to photographers" claims :wink:.

    Just buy an extra one and compare it to your existing one.
     
    Last edited by a moderator: May 4, 2012
  22. wogster

    wogster Member

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    What is typically called a fever thermometer, they should be quite accurate from about 35-40C. If your temperature is above or below that range, it doesn't matter, because you need to immediately go to a hospital for medical attention. They can be a little slow to get a reading though....
     
  23. hrst

    hrst Member

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    Oh, I find they are pretty quick. Of course, a minute or two is recommended when reading your body temperature, but this is because the contact to skin may not be perfect. But stir it in a liquid - it takes just about 15 seconds or less. It comes down to the heat capacity of the sensor/meter which is fairly directly related to the mass of the device.

    The "resetable by shaking" maximum reading feature in some mercury meters might get a little bit irritating, though...
     
  24. Tony-S

    Tony-S Member

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    Good for color but not so much for B&W. I could keep my old one for that, I suppose.
     
  25. Diapositivo

    Diapositivo Subscriber

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    Although I have a mercury thermometer bought in a chemical laboratory equipment shop and an electronic "fever" thermometer, I notice that, in fact, I don't measure temperature at all. Using a CPP-2 with built-in thermostat, I leave the chemicals in the machine while it warms up and I let it warm up (at 38.3 °C) for more than half an hour so that all elements (all plastics, all flasks, the tank etc.) are more or less at the same temperature, around 38.3.
    Using always the same temperature on the Jobo and having basically around 25° in the bathroom I obtain consistent results, so I stopped worrying about the exact temperature, consistency is more important than temperature precision, if you time your baths exactly.

    The infrared beam model seams to me the best choice if and when I decide that I need one. My sister bought one to check temperature on her baby and it's spectacular, no contact with chemicals so no risk of cross-contamination if you want to check more than one bath (although the really critical one for temperature is only the developer).
     
  26. hoffy

    hoffy Member

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    I use an old Ilford mercury thermometer (with an F scale), which I have calibrated against a thermometer my wife bought when we started trying to have kids (apparently, these were supposed to be super accurate to check when a woman is ovulating, or so it goes).