Accurate thermometer for C41

osprey48 · Mar 20, 2012

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.

jscott · Mar 20, 2012

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.

Gerald C Koch · Mar 20, 2012

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.

tnabbott · Mar 21, 2012

jscott said:
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.

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...

perkeleellinen · Mar 21, 2012

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

ras351 · Mar 21, 2012

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.

Lamar · Mar 21, 2012

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

perkeleellinen · Mar 21, 2012

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?

DREW WILEY · Mar 21, 2012

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.

DREW WILEY · Mar 21, 2012

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.

nworth · Mar 21, 2012

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.

perkeleellinen · Mar 21, 2012

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.

osprey48 · Mar 21, 2012

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.

John Shriver · Mar 21, 2012

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.

madgardener · Mar 21, 2012

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.

Mike Wilde · Mar 22, 2012

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.

Lamar · Mar 22, 2012

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

perkeleellinen said:
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?

Tony-S · May 4, 2012

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

benjiboy · May 4, 2012

Patterson certified mercury colour thermometer, they are guaranteed to be accurate to + or- 0.3 degrees C. straight out of the box.

hrst · May 4, 2012

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 .

Just buy an extra one and compare it to your existing one.

wogster · May 4, 2012

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....

hrst · May 4, 2012

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...

Tony-S · May 4, 2012

hrst said:
There is one type of a cheap "household" thermometer that meters just perfectly at 100F/37.8C,

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

Diapositivo · May 4, 2012

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).

hoffy · May 5, 2012

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).

Accurate thermometer for C41

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