Thermometers

Discussion in 'Darkroom Equipment' started by thisismyname09, Feb 14, 2011.

  1. thisismyname09

    thisismyname09 Member

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    I'm in the process of finding a good darkroom thermometer. I've read of the kodak process thermometers, and even managed to find a type 3 for under $40 (to my intense displeasure, it came to me broken). Now it seems these thermometers are all but impossible to find inexpensively; the one I'm watching on ebay is up to $150. Are there any cheaper alternatives with comparable precision and accuracy?
     
  2. Rich Ullsmith

    Rich Ullsmith Subscriber

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    Maybe a Weston? I had two of them, gave one away and broke the other, and since then it has been one Mickey Mouse device after another. Just been too lazy to go find another, but it is what I would recommend.
     
  3. jmcd

    jmcd Member

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    I think real precision is difficult to come by and also difficult to verify. So, I settle for close, and rely on the fact that the thermometer is consistent (black and white, here.)

    I have another back-up thermometer, and it is off by 2 degrees F. So if my main one breaks, I can call the back-up into service, taking into account the 2 degree discrepancy.

    My main thermometer is a Paterson, about $25, and I find it easy to read.
     
  4. thisismyname09

    thisismyname09 Member

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    At the moment I'm working with the same situation; my thermometer is off by a few degrees. I'm looking for a very precise one for color work and the like.
     
  5. BetterSense

    BetterSense Member

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    You can buy lab thermometers at places including Amazon. Prepare to spend >$100.

    My $15 digital cooking thermometers work fine for me, but if I wanted more precision I would buy a PT100 and rig it up with a microcontroller.
     
  6. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    For color work you can use a digital fever thermometer, they are cheap and guaranteed accurate at temperatures around 100F. You can also use 'water bath' thermometers that have an expanded 30-40C scale. I find cooking thermometers to be accurate to 0.2F. For B&W work accuracy isn't all that important, but repeatability is. Unless the column has separated, any liquid thermometer will be up to the requirements imposed by photography. 'Weston' style dial thermometers need to be checked periodically: they are often either adjustable or broken and the stem can be rotated with respect to the dial, changing the reading.

    Simply sticking a thermometer into a beaker of water won't tell you the temperature accurately - but this has nothing to do with the thermometer. Technique is critical to accurate temperature measurement. Some thermometers go to the extent of expecting a certain immersion depth and a certain air temperature.

    The old adage about clocks applies to thermometers: the man with two thermometers never knows the temperature.
     
  7. Reinhold

    Reinhold Subscriber

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  8. Photo Engineer

    Photo Engineer Subscriber

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    A man who owns one thermometer knows the temperature, but if he owns more than one............ :D

    Anyhow, the best Kodak thermometer is the one in a metal case. I have two and they run in the $120 range.

    PE
     
  9. markbarendt

    markbarendt Subscriber

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    Consistency is what's really important.
     
  10. Anscojohn

    Anscojohn Subscriber

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    I bought several Taiwanese Celsius mercury lab thermometers in cardboard tubes in a close-out sale at a science supply house when mercury became a no-no.. The three I have tested are all dead on. I use two of them to check my Paterson which I use to calibrate my Weston dial thermometers.
    They are not the most convenient dudes around--they are about 24 inches long. Anyone wishing one drop a pm. Maybe 20 bucks, plus UPS shipping would cover my cost.
     
  11. yeknom02

    yeknom02 Member

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    This might be a stupid question, but are thermocouples an impractical option?
     
  12. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    A thermocouple is a differential temperature measurement. In order to find the thermocouple's temperature you need to know the 'cold-junction' temperature - the temperature of the connection of the voltmeter to the thermocouple.

    Because you need two temperature measurements - the thermocouple and the RTD (a temperature dependent resistor) used to measure the cold junction temperature - and the problem of maintaining an isothermal connection to the thermocouple, thermocouples aren't normally used for precision temperature measurement. They are best suited to measuring temperatures that are far from ambient - a few hundred degrees to a few thousand. That doesn't mean a thermocouple can't be used for ambient temperature measurements, but there are better ways.

    For electric measurement of temperature at ambient temperatures (-55 to +150C) a platinum RTD is the instrument of choice. The platinum RTD will need calibration - a triple point cell is the normal calibration standard.

    The Omega corporation maintains an information database on temperature measurement http://www.omega.com/temperature/z/zsection.asp
     
    Last edited by a moderator: Feb 15, 2011
  13. Greg Davis

    Greg Davis Subscriber

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    I have both a Kodak Process Thermometer, Type 3 and a Paterson process thermometer. They both read the exact same and I was able to get them both for $25 each. Quite frankly, the Paterson is easier to read and responds to changes faster.
     
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  15. BetterSense

    BetterSense Member

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    Thermocouples suck. They are just a pain. The only reason to use a thermocouple is if the temperature you need to measure is too high for anything else (like greater than 800C) or you need the absolute cheapest thing. A lot of people make the mistake of noting the ubiquity of thermocouples and coming to the conclusion that that means they are good. Even a thermistor would be better for photo chemistry.

    And many platinum resistance thermometers will be pre-calibrated to within photographic tolerances. The behavior of platinum is very well known.
     
  16. flatulent1

    flatulent1 Subscriber

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    I'm partial to this one.

    :munch:
     
  17. holmburgers

    holmburgers Member

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    I have a Jobo Color Thermometer (3321) and I know there's one currently on eBay for very cheap. Glass, mercury, high resolution, very accurate.

    It has incredibly fast response, and a good range, all in Celcius. I've never used a higher end thermometer, but I don't know how it could be better. Compared to a cheap glass one I have, it responds orders of magnitudes faster. Reliably sits on a temperature in 5 seconds or less.

    eBay #320655101791
     
  18. jp498

    jp498 Member

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    My weston dial thermometer has been very reliable for me for 20+ years and hasn't been babied either. Whether it's accurate or not I don't know for sure, but it is very precise in that it helps me develop consistent negatives and I'd notice if I were a few degrees off in the results.

    I shy away from the mercury/liquid thermometers; I've accidently rinsed them in hot water before and *snap*. Didn't even have to drop it to bust it. I suppose having one for reference is fine, but I would not choose to use one on a regular basis.
     
  19. holmburgers

    holmburgers Member

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    I've often wondered about exceeding the thermometers scale. Luckily, it's 55° C so it's possible but I've always been careful.

    It's speed is just really a huge bonus for me; compared to my meat/dial thermometer... well honestly there's no comparison (granted it's a cheap one). The dial takes 30 seconds or more to settle, and since I don't have temp. control on my faucet, getting immediate readings is a must for dialing in 20°C.
     
  20. MattKing

    MattKing Subscriber

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    Here is what I've done:

    1) I found a good, consistent thermometer (in my case a Kodak Process thermometer, but something like a Jobo Colour thermometer would be great as well). I use that thermometer for calibration purposes only;
    2) I use on a regular basis a cheap digital kitchen thermometer with a probe at the end of a cord.

    The trick is that I regularly check the digital thermometer against the Process thermometer. If the digital thermometer wanders over time, I can easily compensate for that. In the case of my current digital thermometer, it has been really consistent.

    In my experience, the digital thermometers suffer more with problems with water ingress than they do from erratic behaviour. The design of my current thermometer seems to prevent that problem.
     
  21. jeffreyg

    jeffreyg Subscriber

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    I have had for very many years and still use two Weston dial thermometers. They read room temperature at the same as our digital thermostat and both read the same also at 68o solutions. So if they are off they are both equally wrong and have no apparent effect on my negatives.

    http://www.jeffreyglasser.com/
     
  22. michael9793

    michael9793 Member

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    Try B&H they are not bad. I think you are going over board with this accurate stuff. why digital. plain dial darkroom thermometer from any photo store. Paterson I think has one. remember the KISS. keep it simple stupid.
     
  23. georg16nik

    georg16nik Member

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    I use old-school mercury thermometer, waiting to see something more precise!
    Have some friends who found their digital or "photo" grade thermometers are off by up to 2 ~ 5° C ... ouch
    There is no evidence whatsoever, that electric/digital thermometers rely on capacitors, resistors and other stable parts that holds their data value over time, so they are supposed to shift their reading in one direction or another, day after day..
     
  24. traveller

    traveller Member

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    Why not buy a lab thermometer like this one? Very precise and not extremely expensive. Check it against and note the deviation of a cheap thermometer. Store the precise in a secure place and work with the cheap one. Check again every 6 months.

    Maybe you know someone working in a lab? Normally they get a good rebate :wink:
     
  25. Dave Martiny

    Dave Martiny Member

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    They say the length is 460mm.

    Holy smokes!
     
  26. traveller

    traveller Member

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    Precision and being able to read the scala without a loupe has a price. And you only need it to control your other thermometers.

    In the meantime I have seen there is another thread where everything is summed up real good Link