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How long does a dial thermometer stay calibrated?

J Rollinger

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Chicago, IL
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I calibrated my dial thermometer last September by using a Kodak Type 3 and now im noticing my negs seem to be over developed. I no-longer have the Type 3 so i bought a Paterson color thermometer and was surprised to see that my dial thermometer ran 2 degrees hotter than the Paterson color thermometer. How often should i re-calibrate my dial thermometer?

Thanks..
 
The dial thermometers go out of calibration pretty easily in a community darkroom situation, based on past experience. Just found my Kodak process thermometer -- time to check the digital thermometer, a couple other mercury thermometers and a handful of dial thermometers again!

(just going thru this for my understanding)...If your dial thermometer reads 2 degrees hotter than the Paterson, that means that if the Paterson reads 68F, then the dial reads 70F. Thus the developer is 2 degrees colder than you think it is (relative to the Paterson). You should be under developing, if anything. If you adjust to match the Paterson, then the developer is going to be two degrees even colder...but the correct direction to go if you are over-developing.

I would adjust the dial to the Paterson, then check it against the Paterson before every developing session. Experience will tell you how often to check it! Every dial thermometer is different!
 
Your exactly right, i was looking at the temp difference in the opposite way. So i was actually developing at 2 deg cooler? I have been doing mostly push processing and longer inversions to obtain the contrast i want and now i realize that my method is most likely the cause of my negs being overdeveloped unless i have shutter issues that is causing over-exposures? If it is my method should i just calibrate the dial to the Paterson, are they known to be accurate?
 
Hummm

It makes me wonder how long before an olde tyme photographer-geezer goes out of whack. Maybe 'bout ten years ago in my particular situation.
 
snapguy said:
It makes me wonder how long before an olde tyme photographer-geezer goes out of whack. Maybe 'bout ten years ago in my particular situation.
Click to expand...

You could try re-calibrating yourself against a younger whipper-snapper photographer. Then adjust your outlook accordingly. Works for me.

s-a
 
J Rollinger said:
I have been doing mostly push processing and longer inversions to obtain the contrast i want and now i realize that my method is most likely the cause of my negs being overdeveloped unless i have shutter issues that is causing over-exposures?
Click to expand...

Your question begs for clarification on how you are judging the negative.

Unless there is a truly gross over exposure (maybe say 4 or more stops over), exposure probably isn't the problem. Exposure changes do not change the shape of the film curve, just where the subjects fall. Exposure should be judged by where the subject matter in the shadows fell. If you didn't get the shadow detail you wanted on the negative you under exposed, if you have more shadow detail than you planned on you probably did fine. Get a magnifying glass and look for that detail on the negative or print light to see where detail runs out.

Extra exposure typically just requires more print exposure to compensate, nothing else.

The best way to judge proper negative development is to test by printing to your standard paper. If it prints "pretty" without needing contrast adjustment development is right.

J Rollinger said:
If it is my method should i just calibrate the dial to the Paterson, are they known to be accurate?
Click to expand...

I have various thermometers and none of them agree completely. As long as I only use one thermometer, I don't have a problem. Accuracy is fairly important (you need to be in the right ball park), but consistency is what is truly important. It doesn't matter if your real norm is 64, 66, 68, 70, or 72; what matters is that your thermometer indicates the same number every time.
 
markbarend

I have various thermometers and none of them agree completely. As long as I only use one thermometer, I don't have a problem. Accuracy is fairly important (you need to be in the right ball park), but consistency is what is truly important. It doesn't matter if your real norm is 64, 66, 68, 70, or 72; what matters is that your thermometer indicates the same number every time.

I think Mark sum's it up. If you have more than 1 thermometer you will never know the temperature. If you'r thermometer can be calibrated it will forever need calibrating. I use the Paterson Color Thermometer and it does not need batteries, does not glow in the dark but I will live and die with it.
 
J Rollinger,

After I broke my other glass reference thermometers (blue liquid no mercury spill here)... I happened to have just picked up a replacement glass thermometer that just happens to be a Paterson Color Thermometer. I notice a small scratch in the glass at around the 65 1/2 degrees F mark. Do you see or feel such a scratch.

I believe that is the immersion point for calibrated readings.

Set to the bottom of my glass beaker, it also reads 2 degrees colder than my USB and Dial thermometers in the same beaker. But when I lifted the Paterson up until that mark... All three thermometers agreed.

Conclusion: It's colder at the bottom of the glass. -OR- That mark is an important indicator of how deep you are expected to immerse the thermometer.

I've also got the original package, it claims to be accurate to +/- 1/4 degree F (0.14 degrees C).

I don't think 2 degrees either direction would cause as much overdevelopment as the other factor you described: developing for longer time to get higher contrast. I don't know about the age of your developer, but I've had old D-76 give me more development than I planned.
 
Thermometers have been off since Fahrenheit invented his temperatures scale. He fixed his scale on the coldest temperature that he could obtain with an ice and salt mixture and the other as the temperature of the human body. Unfortunately he used his wife as his subject and she was running a slight fever that day.
 
I gave up on the dial thermometers because they just don't stay in calibration, especially if they get knocked about some, which is inevitable. Bought 3 of the cheap glass ones from Freestyle a year or two ago (see link below) and they work perfectly. They all read exactly the same too. I even dropped one and busted off the tip, but some epoxy stuck it back together, and it's still accurate. Try doing that w/ an expensive dial thermometer.

Old D76 has caused me a lot of grief too. The only sensible way to use that developer is to buy it in the quart sizes and use it up quickly, or switch to TD-16, which will remain stable for months and months.

http://www.freestylephoto.biz/62010-LegacyPro-6-inch-Glass-Thermometer
 
APUGuser19 said:
[h=1]Thread: (there was a url link here which no longer exists)[/h]
You mean it was accurate once?:confused:
Seriously, I've never seen an accurate dial thermometer. I suppose it can happen.
Click to expand...

Mine have always been accurate, in the sense that they are reliable and consistent; they just aren't well calibrated.
 
Yesterday the dial thermometer was 2 deg from the Paterson color thermometer and now today its .5 deg off. I think its clear that the dial therm is having issues. Im going to stick with the glass Paterson and buy a spare just in case i break it which is likely to happen.
 
J Rollinger said:
That i dont know.. Its suppose to be as accurate as a Kodak Process Type 3 being within .25 degrees.
Click to expand...

So If I were to think my thermometer might be running a little "hot", I'd probably be wrong. Makes sense to me.
 
You can't beat a good mercury thermometer.
 
man with two thermometers never knows the right temperature
 
Running a university darkroom, we had a dozen or so various dial thermometers -- glass would not have lasted a week! I checked them on a regular basis and calibrated them to the in-line dial thermometer on the water supply. If they were off, at least they were all off the same amount.

I have a digital one now -- shaped similar to the dial ones. Easy and quick to read!
 

For critical industry use,they should be calibrated in regular intervalls of about a year and compared to a reference sample prior to every use.In addition,You should probably conduct a measurement systems analysis MSA once just to see what you can expect from the instrument in your environment but I don't know of anyone who goes that far than myself.It's a Six Sigma Black-Belt discipline and a bit too involved for an amateur darkroom to be honest.Nevertheless ,it cabn be very revealing and sobering to see how trystworthy these measurements really are.
 

I didn't believe a word of that - until I noticed who you are. After reading your book I believe you do conduct an annual analysis on your thermometers.
 
Man who has two watches never knows what time it is.

That said, I have a Kodak process thermometer and two dials. The Kodak is used to calibrate the others and never used as a working instrument. The Weston is 30+ years old and I never had to calibrate a second time. Be gentile and do not throw it around or subject to extreme temps.

The other is an off brand and reads 1 degree too high. It has never changed. I cannot adjust it.

All the film developing times were calculated using the dials which I check occasionally .
 

I'm a big fan of the Intellifaucet.it regulates the water temp within one degree C within a few seconds and keeps it stable from then on.It's not cheap but perfect
 
RalphLambrecht said:
I'm a big fan of the Intellifaucet.it regulates the water temp within one degree C within a few seconds and keeps it stable from then on.It's not cheap but perfect
Click to expand...

Ralph, you are the first person I have heard of with one of these instruments. At what litre per minute flow rate, are they supposed to be within their parameters?

I ask as I am considering updating my 27 year old darkroom with one of these and the flow rate of water required to make these work correctly has been one of my concerns. Your one degree C stability notation, is quite promising and music to my ears.

I switched to electronic thermometers decades ago, one of the better things I did. These days one can get a small pocketable fully waterproof electronic thermometer that is not only calibrated, but certified, for not too much over $130 USD last time I looked. Not only that, it is possible, if one carefully follows the correct procedure, to re-calibrate these thermometers oneself.

Mick.
 
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