C-41 film processing image quality and absolute temperature

[Tom Kershaw]

In light of recent discussions on APUG about the accuracy and precision or otherwise of various methods of measuring the temperature of processing solutions, I have a question concerning C-41 processing, namely, how important is the accuracy of the absolute temperature to maintaining image quality?

If I recall correctly the C-41 process is supposed to run at 38.7ºC in my Jobo ATL-2300. Assuming correct mixing and activity of processing solutions, if the real temperature of the solutions was 37.7ºC or 39.7ºC, would this adversely or materially affect image quality, grain, sharpness, or anything else?

Tom

 

[hrst]

37,7C rather than 38,7 .

The biggest effect is that you will get a pull or push process; wrong contrast and colour mismatch (crossover). Too high temperature increases contrast and too low decreases it. Color layers don't react exactly similarly to the variations, which causes contrast mismatches. If you scan your negs, this doesn't probably mean anything as it is fixed in levels or curves tool.

However, I tend to think that these problems are fairly small; especially, if you scan, then the processing temperature and time doesn't play so big role. If you print your negs, current RA-4 papers tend to be quite high in contrast so you don't probably want to overdevelop but rather err to the underdevelop.

But, 1C deviation IS quite big. I would say that 0.5C is okay for me, some people would want 0.2C precision.

 

[Tom Kershaw]

But, 1C deviation IS quite big. I would say that 0.5C is okay for me, some people would want 0.2C precision.

I agree, my post is in the context of what is accurate... As you're probably aware the ATL-2300 is automated so the film (for example) does get 3 minutes 15 seconds development each time. I use the Fujihunt 5 litre C-41 Xpress kit.

Tom

 

[nickandre]

I'm told that it takes 5 degrees F to cause crossover. I think a degree F either way will not hurt your cause that much. I don't think my processing is that accurate but I get very good results nevertheless. The assumption is in heat transfer between the water bath to the cylinder. It's very easy to keep a tub of water very close to a temperature, but very hard to know what temperature to use. I know it's somewhere between 100.5 and 102 degrees F, and I know it changes based on how much water is in the bath (ie, how much of the metal tank is covered.) For now I pour in at 102, and keep the water bath 101 to 102 and pray. Seems to be working.

 

[Photo Engineer]

You stand the risk of getting color balance shifts and contrast changes in the film if you move too far, but there is some leeway built in. The standards we used were +/- 0.15 degree C for "perfect results" centered on 37.8 deg C. or, +/- 1/4 deg F centered on 100 F.

I have 2 Kodak process control thermometers that are nearly 1 foot long and use mercury. They are in stainless steel jackets and last I looked were pretty expensive. They match, but differ from most every other thermometer I own, dial or liquid. I have at least 6 thermometers.

The interesting thing is this. If you are off by a degree and repeat that over and over, you will at least get consistant results. That is, if you are within 1/4 degree F of your own center point.

This gets back to the old thread here though, if you have one thermometer, you know the temperature, but if you have two, you are not so sure anymore.

PE

 

[nickandre]

This gets back to the old thread here though, if you have one thermometer, you know the temperature, but if you have two, you are not so sure anymore.

PE

I once processed with a thermometer that was 6 degrees cold. I knew the temperature was correct though...

 

[Ed Sukach]

From experience...

I have processed C41 film in a JOBO CPP-2 inadvertantly set (not reset from RA-4 development) at 35 Celsius - -3 degrees C from the required 38 C; similarly, I have processed RA4 paper at 38 C - +3 high.
In neither case was the color balance or contrast, or anything else that I could notice, significantly enough "off" to cause any sort of unusual problem in printing.

IMHO, it is very nearly impossible to control any process likely to be used in anything but an ultra-sophisticated Industrial Lab / Production facility to anything closer than +/- 1 degree F... and even so, we continue to produce consitently high (and I mean HIGH!!) quality images.

 

[Photo Engineer]

Ed;

To be fair, the paper is less temperature sensitive than the film, so your results in that regard are to be expected.

PE

 

[Athiril]

When I was processing C41 with a kit using, I used the alternative times it gave for 31c, as it was much easier to keep a consistent temperature, in fact, ambient in summer for sitting water is around 25-26 so it doesnt drop, unlike ~38, which was great.

 

[GeorgK]

It depends on the type of film, maybe also on the type of chemicals. Some films are very forgiving, others react very sensitive to changes in processing conditions. In some cases, a slight deviation from "standard" might gain better results. The fact that c-41 is an "industry standard" does not mean that all combinations of film and chemicals produce their best results exactly at standard conditions.
Small-scale home processing is never 100% equivalent to processing in a commercial c-41 machine, so one has to make fine adjustments anyway.
And: although there is always the obvious "I processed 5 degrees off and had perfect results"-posting, such findings are .... exceptional. Plusminus 0,5 degrees celsius and plusminus 5 seconds should be easily obtained in a home darkroom. Remember that 0,5 degrees celsius (very roughly) equal about 15 sec in processing time.
I guess the biggest variable in C41 home processing is the uncontrolled aging of the developer.

Georg

 

[Athiril]

When it gets too old - you can use it as a colour developer in colour reversal and just let it sit for a fair bit longer too completion - I got decently accruate results with Rodinal (first dev)/C41 (colour dev) for Astia, wacky results for C41 xpro'ed as reversal in C41 though...

 

[Tom Kershaw]

I've just processed 3 rolls of C-41 120 format. The temperature pre-programmed on the Jobo is set at 38.0ºC.

Tom

 

[Photo Engineer]

Tom, that may account for the temperature drop as the water is recirculated.

However, another thought struck me. All thermometers have an immersion depth marked on them, which should be the length of the thermometer submerged in the liquid being measured. This is usuall (in the US) 2", 3" or TI (Total Immersion). If you don't follow the guide marked on the thermometer, then the reading will not be as accurate as it could be and this may explain some reported differences.

IDK how this applies to stainless steel stem thermometers, but I have seen differences based on depth of solution being measured.

PE

 

[Neufemmes]

I have a question about my old JOBO-tank (CPA). Normally the part where the bottles are in and the part were the tank "rolls" are connected and the water runs through and you have in both parts the same temperature. But last night, i noticed that that wasn't the case anymore with my tank and the part with the chemicals was warming up and the other part wasn't. I'd like to ask if that would have a consequence for developing my negatives (120, color, Tetenal). And does anyone know how i could resolve it, there's probably dirt in the part inbetween how could I make it free again? Thanks!

 

[madgardener]

I'm glad this thread was resurrected. Currently I am using a digital temperature controller wired to an outlet and a fish tank heater for my C-41 and am curious about either calibrating it or purchasing something. When I develop myself, my negatives come out with a magenta haze over everything,and some very extreme grain. I'm guessing it's the temperature. Should I invest in a true PID controller instead?

 

[Photo Engineer]

C41 is best when all of the temps are at the values in the instructions. If you vary, you get results that are off the norm.

Any action to bring the temps in-line will help.

PE

 

[CHX]

How do people get the temperature that accurate? With colour I tend to wind up crossing my fingers and hoping, as I have never found a foolproof way of keeping the temp within +/-2c of where it's meant to me. Admittedly this was in my kitchen at home using a kettle and bucket of hot water when the chemical bottles wedged in it.

 

[Tom Kershaw]

With regard to processing in a new Jobo CPP-3 which is less sophisticated compared to the ATL-2300, I tend to leave the machine running with tempered chemistry for a while (e.g. 30mins to 1 hour) before running a batch of film.

Tom

 

[bvy]

How do people get the temperature that accurate? With colour I tend to wind up crossing my fingers and hoping, as I have never found a foolproof way of keeping the temp within +/-2c of where it's meant to me. Admittedly this was in my kitchen at home using a kettle and bucket of hot water when the chemical bottles wedged in it.

Images of Goldberg Machines in people's bathrooms to process C-41 is, I think, what puts a lot of people off to ever trying it. I use a simple water bath at a particular temperature in a Playmate cooler, and a few tempering prewashes in my Paterson tank. The developer goes in at 101F and, every time, comes out at 99F. I figure a loss of one degree with each pour (developer in, developer out). That's close enough to 100F for me. To try to put more control around this is splitting hairs that I can't even see.

What's important to me relative to this is that I get results that I can easily print without dialing in crazy filtrations. And I do.

 

[mklw1954]

I also get good temperature control using a small 6-pack cooler. I bring the empty tank containing the reels/films to the developing temperature by starting with water 2-3 degrees higher than the developing temperature in the cooler. I monitor the cooler water temperature with a digital thermometer with a wire probe (calibrated to my Paterson color thermometer), adding hotter water to the cooler until the cooler water temperature is constant at the developing temperature (takes 30-40 minutes while I measure out and filter the chemicals). This equilibrium indicates the tank is at the right temperature. Then bring the pre-wash water, developer, and blix to the developing temperature in a separate water bath. Place the tank in the cooler when not agitating and continue to maintain the right temperature in the cooler during the pre-soak and developer steps. The blix step can be +/- and stabilizer is at room temperature. Results are great.

 

[lhalcong]

I intentionally processed a test roll (Fuji) , (portrait of kid) at 95F , way below the norm just to be able to see what happens and tell the difference vs. a well processed roll. Yes, undeniably the roll processed at 95F was lower in contrast and it had a cyan cast on the skin. I am not sure what color crossover is or how to tell if I had that ? . However, to my surprise this was so easily fixed on the computer after scanning with just a few clicks like someone already mentioned here. Although I didn't try printing it in the darkroom, I wonder how difficult if any will be to correct on print as well. I am thinking it shouldn't be that difficult either. So my conclusion was that if the pictures are to be scanned and digitized, the off-temp becomes no so critical. Of course, I still process correctly at 100F.

 

[bvy]

Although I didn't try printing it in the darkroom, I wonder how difficult if any will be to correct on print as well. I am thinking it shouldn't be that difficult either.

Doable, perhaps, but speaking from experience, consistency is the darkroom printer's best friend. I keep a spreadsheet of all of my color prints made, the film used, the filtration, and some other values. When it comes time to print a certain negative, I can look back at the filtration values used given that film and arrive at a good starting point. If you're developing color negative film at temperatures that are always slightly different, you don't have that luxury.

 

[MattKing]

I intentionally processed a test roll (Fuji) , (portrait of kid) at 95F , way below the norm just to be able to see what happens and tell the difference vs. a well processed roll. Yes, undeniably the roll processed at 95F was lower in contrast and it had a cyan cast on the skin. I am not sure what color crossover is or how to tell if I had that ? . However, to my surprise this was so easily fixed on the computer after scanning with just a few clicks like someone already mentioned here. Although I didn't try printing it in the darkroom, I wonder how difficult if any will be to correct on print as well. I am thinking it shouldn't be that difficult either. So my conclusion was that if the pictures are to be scanned and digitized, the off-temp becomes no so critical. Of course, I still process correctly at 100F.

You will have colour crossover when parts of your negative have one colour cast, while others have a different colour cast. Even with digital techniques, they are extremely hard to print correctly.

Usually, the crossover is observed where darker parts of the image have a different colour cast than lighter parts.

Temperature variation contributes to this because it affects the relative speed/sensitivity of the colour layers.