Actual temp in a Jobo drum C-41

[sfaber17]

I noticed a thread or two that said one must do a pre-rinse with a jobo in order to pre-heat the drum
and reels. A pre-warm isn't good enough. I did some tests to see what that effect is and found it to be quite true. Just setting an autolab to the right temperature can be deceiving. I set mine to 38.0 degrees and did a 5 min pre-warm using a 1520 2 35mm reel drum with 270ml water substituted for developer. I used an extreme precision mercury thermometer that was accurate to .028 deg C. with .1 deg divisions. After the water was pumped in and spun for 15 sec or so, I reset the processor, removed the drum and dumped it in a pre-warmed styrofoam cup with a pre-warmed thermometer. The water was only 35.5 deg C. I was surprised the few rolls of film I did previously scanned out so well.
Next, I tried to figure out how to get the actual temp to 38.0 deg. I ended up setting the rinse water to 39.5 deg, doing a 30 sec pre-rinse, and setting the processor to 38.8 deg. With that machine, you can read out the water bath temp and the solution temp, which were both at 38.5 deg. My water bath is about .5 deg warmer than the jobo says, but the solution temps are exact to the nearest .1 deg C. With that combination, my "developer" was 38.0 deg during the complete interval. Maybe I'll try similar tests on a CPP2. There you can only control the tempered bath, so I would think you need a couple short pre-washes to get it up to temp and a little elevated bath temperature.

 

[Photo Engineer]

There is a long thread about prewarm / prewet.

I suggest that you read it.

You need more than one prewet under some conditions.

PE

 

[Sirius Glass]

When I need to warm the chemicals, I give the water bath in the Jobo and the chemicals hours to temperature stabilize.

 

[Rudeofus]

Your data set is surprising, because you report a 2.5 deg temperature drop (38.0 ---> 35.5) if you set everything to 38 °C, but a much smaller temperature drop at a higher temperature (39.5/38.5 ---> 38.0). Were these measurements taken with the same processor?

 

[sfaber17]

There is a long thread about prewarm / prewet.

I suggest that you read it.

You need more than one prewet under some conditions.

PE

Thanks, I'll look for that. I believe you would need a multiple prewet lacking an elevated temp pre-rinse.

 

[sfaber17]

Your data set is surprising, because you report a 2.5 deg temperature drop (38.0 ---> 35.5) if you set everything to 38 °C, but a much smaller temperature drop at a higher temperature (39.5/38.5 ---> 38.0). Were these measurements taken with the same processor?

The first experiment was with no prewet, so the drop was due to 270ml of solution. The second test used the processor's pre-wet stage which pumps quite a bit more solution than the 270ml. I also found later that I have to run the rinse water temperature test to warm up the insides of the processor or the initial rinse water temp would be lower than what's coming in from the water panel.

 

[Rudeofus]

Time for a quick test then. I took a Jobo 1520 tank and prepared a small bucket with hot water. Ambient temperature was 28°C, water temperature started at 50.0 °C. I removed to top cap from my tank and placed a thermometer through the funnel/spindle. I put the tank into the bucket of hot water and held it down such that it would be fully immersed but that no water would spill to the inside of the tank. Here are the temperatures I recorded:

time [minutes]	temp [°C]
0.0	28.0
0.5	32.0
1.0	32.0
2.0	32.2
3.0	32.8
4.0	33.2
5.0	34.0
6.0	34.6
7.0	33.1
8.0	35.8
9.0	36.4
10.0	37.2

10 minutes into the test I removed the thermometer from the tank and inserted it directly into the hot water. At minute 12 I measured 44.9°C, which is a noticeable drop from 50°C, but not the main reason for the slow rise of temperature inside the tank.

From a thermal standpoint you have the same situation with 28°C ambient and 50°C water that you have with 16°C ambient and 38°C water. Realize that my test as performed is a lot more optimistic that the situation you likely have with rotational processors: My tank was completely immersed in that water, whereas it's at best 25% immersed in a rotary processor. My tank didn't have 75% of it exposed while wet, which would further lower its temperature.

Unless you have ambient temperature close to 38°C, a five minute immersion of the tank prior to development is completely ineffective. With these results we should not be surprised to see that a prerinse makes a big difference.

 

[sfaber17]

Nice test. It suggests that a pre-warm of 30 min might work.
I did another run, this time using the first 2 bottles as a pre-rinse supply. The temperature was set at 38.4. One run using 30 sec from each bottle and another using 40 seconds. Both gave a temperature of 37.7 degrees. I preferred the original method for hitting 38.0, so I ran a 35 mm roll and it turned out nice. It did look quite a bit denser than my other films, however I was using a new camera. I'll try do some RA4 prints from it.

 

[mnemosyne]

I did some temperature tests today with my CEP2 as I want to give C41 development another try. I am using 2500 series tanks with magnet base (no lift). I found that when you use the lid with the inner (funnel shaped) part removed, it is possible to stick a thermometer into the pool of liquid inside the tank while it is rotating (with 2 reels loaded). This is probably as close as it gets to "knowing" the actual temperature of the developer during development and should help determine the correct temperature for water bath and solutions. Preliminary result: With the water jacket at 40°C (stabilized for several hours, measured in the area where the drum moves through the water), plus two prewet runs with 300ml of 40°C each, the developer (300 ml) needs to be preheated to 1°C above target (= 39°C) to have a constant developer temperature of 38°C from the start to the end of the development time.

 

[davedm]

Rechelle, A

Could you repeat your test with Water Jacket at 39°C please ? Also report ambient temperature there.

Thanks

 

[DREW WILEY]

Jobo drums are fairly thin ABS, so they don't insulate ideally, nor do they transfer heat ideally from the water jacket ideally like stainless steel does. But with drums in general, the key is to warm the air inside first with tempering water, then have enough actual volume of developer in the drum to maintain liquid temperature for the duration of the solution. Well, Jobo drums don't fill and drain fast either, so you need to be very religious about your timing and be certain it is long enough to factor in very consistent fill and drain times. It also greatly helps if the ambient air temperature isn't too much below the chemical temperature. You can also measure you chemical temperature coming out. With attention to detail and practice, this
can all usually be worked out.

 

[mnemosyne]

Okay, I redid yesterday's tests, this time with the water jacket at 39°C (38.8-39.0°C, to be more precise). Ambient temperature during the whole time was between 19.6 and 19.8°C. I made three runs with the two prewets of 300ml at 39°C and 2'30" each. "Developer" (water) was heated to a target temperature of ~39°C. Then I measured the actual temperature of the developer in the rotating drum during the 3'15" of development. To summarize the results:

• drop off between preheat T of developer and first measurement in rotating drum ranged from 0.8 to 1.0 degrees
• further drop off between initial measurement and end of 3'15" development time between 0.4 and 0.6 degrees

I then did a further two runs with the water jacket at 40°C (of course letting everything stabilize for 2 hours)

• T drop off between preheat T of developer and first measurement in rotating drum was 0.4 and 0.5 degrees respecitvely (much less than what I measured yesterday). This resulted the actual T during "development" being above target, but could be easily adjusted for by lowering the preheat target of the developer
• further drop off between initial measurement and final measurement was 0.2 degrees in both runs

I realize this is far from scientific, questions remain and the methodology of measurement introduces its own set of problems (for example, it is unclear how big the insulating effect of the funnel and cap removed for the test are, but it can be expected that T dropoff during development is lower when both are in place); However, at least for me it seems to indicate that with my setup and the conditions I work under 40°C for the water jacket is preferable to 39°C. I will have to do more testing to better understand how much the preheat temperature of the solutions differs from the actual processing temperature in the drum.

 

[mnemosyne]

• T drop off between preheat T of developer and first measurement in rotating drum was 0.4 and 0.5 degrees respecitvely (much less than what I measured yesterday).

I think I found out why: I remember now that on day one I gave the drum three inversions just immediately after filling with developer and before sticking it on the Jobo. On day two I attached the drum immediately after filling. Shows how much effect such seemingly small details can have!

 

[davedm]

Rechelle,

Thank you for repeating the tests. I was actually hoping that 39°C might turn out to be better.

Thanks

 

[mnemosyne]

This is a follow-up to my earlier posts about getting the process temperature into the ballpark when using the Jobo CPE2.
I did some further testing with the method described above, but had problems to get repeatable results until I changed some fundamental things.

• The first change is that in addition to the pre-rinse @40C for 5 min, I pre-warmed the Jobo tank (2500 series) in the water bath of the CPE2 for 30 minutes. Just let it sit (film loaded) upright in the elevated area where the tank is normally mounted for rotation. After 30 minutes the temperature inside the tank has risen to about 30C. It seems this is a more reliable starting point than starting the pre-rinse right with the "cold" tank. Of course the lower part of the tank, which is immersed in the water bath, will get much warmer than the rest, but this is evened out during the pre-rinse step that follows
• The second change is that I chose to pre-rinse with 500 ml of water @40C for 5 min instead of two pre-rinses of 260 ml each for 2m30s @40C. This seems to help in getting more predictable results and also makes it easier to concentrate on adjusting the developer temperature right on point at the end of the 5 min pre-rinse. Speed setting used is "2" (fast), same as for processing

After implementing these changes I finally managed to get repeatable results. I had to lower the pre-heat target temperature of the developer to 37.8 C though. With that, after pouring in the developer in the pre-heated tank and two inversions, the temperature reads between 37.6 C or 37.7 C (the digital thermometer I use reads 0.2C lower than my mercury lab grade thermometer in that range, so the corrected value is more like 37.8-37.9 C). Temperature will rise very slightly (about ~ 0.1 degrees) during the 3h15m of processing. So it seems I am finally within spec, at least on paper

For the protocol, I summarize my procedure (your mileage may vary):

• NB: I do not use a lift; I do not heat any chemicals inside the Jobo, everything is done externally in a 5 liter bucket with warm water; my ambient temperature is 20.0 C plus/minus 0.5 C
  
• Fill Jobo with water (water level just high enough to cover the white rollers completely) and pre-heat until temperature in the area of the rollers reaches and stabilizes at 40.2 C
• Load film in tank (two reel 2500 series tank), let tank sit upright (red cap removed) in the area close to the rollers for about 30 minutes
• Pre-rinse with 500 ml of 40.0 C water for 5 min at (speed "2")
• In the meantime adjust 260 ml of developer to exactly 37.8 C
• Pull tank, thoroughly drain pre-rinse water, pour in developer, close tank, two quick inversions, attach to the Jobo
• After 3 m 05 s pull the tank and drain developer (10 s drain time)

 

[sfaber17]

This is a follow-up to my earlier posts about getting the process temperature into the ballpark when using the Jobo CPE2.

It looks like you have good control of things that way and suspect you will get standard results. It would be more convenient to use the jobo for the chemicals and not have a separate water bath. I'm also wondering if the pre-warm is largely unnecessary given the pre-wet, and wonder if you could shorten the pre-wet to a minute and get the same result?

I have obtained C41 control strips and a strip reading densitometer. I'll post the results soon maybe in a separate thread, but basically I was able to get within control limits both by: no pre-wet, 6 min pre-warm, extend dev. time to 3:30, or by pre-wet with 103 degF water, and 3:15 standard times, (although my temp was a half degree warm which did show as a bit too active). I don't think I'll use my pre-wet with the 103 deg water method because it is hard to control with the tempered water supply to the jobo (including cooling effects to the tube inlet), so I'm going to try 2 pre-wets with jobo tempered water instead and verify control limits. One good thing is the tests do not show any problem with using a pre-wet.

 

[mnemosyne]

It looks like you have good control of things that way and suspect you will get standard results. It would be more convenient to use the jobo for the chemicals and not have a separate water bath."

The reason I don't use the Jobo for keepin the chemicals at temperature is that the red plastic thing that is supposed to keep the bottles and beakers from floating around is broken and I have trashed it. In my case it's not as inconvenient as it sounds, as I use a small tank which needs only 260ml chemistry so I can simply put a 5 liter bucket with warm water in the sink and keep the small Jobo beakers with developer, bleach, fix and final rinse in there.

I'm also wondering if the pre-warm is largely unnecessary given the pre-wet, and wonder if you could shorten the pre-wet to a minute and get the same result?

The idea with the pre-warm is that it gives me a defined starting point for the temperature of the tank at the moment when I start the pre-wet. During cold winters my darkroom gets rather cold (~10 C) and the tanks and reels are also dead cold. OTOHO, during the hottest period of summer the temperature will go up to 24C, so the idea was to use a pre-heat to even this out. I put a thermometer in the tank and wait until the air inside reaches 30 degrees. Maybe it is overkill and it would work as well without it, but I am consider myself lucky to have stumbled over a procedure that works, so I will simply stick to it unless it gives me problems.

 

[mtjade2007]

The idea with the pre-warm is that it gives me a defined starting point for the temperature of the tank at the moment when I start the pre-wet.

To deal with this you may want to try two steps of prewet each time with max amount of heated water. I use a Jobo ATL-2300 for my C-41 processes. It gives me the convenience of automatic two steps (can go to 3 if I want) of prewet. I know the actual temperature inside the tank may not be up to the 100 degree F still but it seems to have worked well enough for me. I always set my temperature bath to 100 degree. The process time has always been 3'15". This includes the time for chemical pouring and draining. I think my Jobo ATL-2300 takes about 5 seconds to pour the developer for 2 rolls of 220 film and about 10 seconds to drain. I mostly process two 220 rolls at the same time. I know that much of 220 film in the tank could lower the developer temperature a bit more than a single roll of say 24x35mm would. But the result has been pretty good. My prewet time is 30 seconds each only. I think I set the machine to pour about 600 ml of prewet water each.

Without the prewet steps my films always came out very poorly developed. I wasted a lot of films and chemicals because of that. I can say the result being pretty good with two steps of prewet by how easy the developed 220 rolls were scanned by my MF film scanner. The scanner scans easily if the negative is correctly developed. Otherwise it would be always very difficult to scan.

 

[sfaber17]

To deal with this you may want to try two steps of prewet each time with max amount of heated water. I use a Jobo ATL-2300 for my C-41 processes.

I agree. That was my next test, and it worked out nicely within control limits with a test strip. I was using 38.0 deg C but may bump it up a few tenths since the values were a hair low. I'm using basically the same machine - ATL-2200. This method should allow any drum to be used without the need to calibrate each drum. I think it is what others have settled on from what I remember reading.

 

[mnemosyne]

I consider trying this route (two prewets with maximum capacity instead of prewarm plus one prewet). The situation for me is a bit different than with an ATL, as I don't have a lift and have to take off the tanks and fill and drain manually.

For the moment, I have used my described method to actually develop my first test rolls (all 35mm). I will report in separate thread.

 

[sfaber17]

Your case is a bit different, so as long as your method is getting it up to temp. it should be good.