A New Tool for the Darkroom

The CompnTemp Compensating Developing Timer

By Eric Biggerstaff and Alan Ross



Just when we thought the darkroom was fading into history and no new products were on the horizon, a new timer is on the market that will be a welcome addition to the traditional photographer’s toolset. The CompnTemp compensating developing timer is a simple, easy to use and inexpensive alternative to the now discontinued Zone VI compensating timer. CompnTemp is a very accurate way to get repeatable results while developing prints or negatives, and this timer offers the user greater control when developing both negatives and paper than its Zone VI predecessor.


A couple of years ago, large format photographer Curt Palm attended an Alan Ross field workshop and became interested in the Zone VI timer Alan described using in his darkroom. Curt, a staff scientist at Stanford where he works as a scientific application developer, decided he could create an alternative to the now discontinued Zone VI timer. After many months, and many versions, the CompnTemp compensating development timer was created.


CompnTemp itself is software rather than hardware and the easy to use program is designed to run on either a Windows (XP and Vista, 98 was not tested but should work) or Mac OS X based computer. Furthermore, the computer needs to have a minimum of Java v1.4 installed. The timer consists of four parts: the software, a laptop (or any other suitable computer), a “Go!Temp” USB temperature probe and a clear, red plastic sheet to place in front of the computer screen to act as a safelight.


The program reads the developer temperature using the USB probe and compares the developer temperature to a target temperature, then compensates the development time based on the difference between actual and target. The “Go!Temp” temperature probe is manufactured by Vernier and is a separate item (see pricing and purchase information at the end of the review).


You can use the CompnTemp program without the probe to count up or down in Real Time or you can enter the target and real temperatures manually and CompnTemp will compensate based on the values you have entered. (See fig. 1) When using the probe, CompnTemp constantly displays the actual temperature and will adjust for any fluctuations in developer temperature during processing, not just for the initial difference – a real boon for those who have trouble keeping temperatures stable in their darkrooms.


The CompnTemp program features the following:


q      Toggle between real and compensating times

q      Read out in Fahrenheit or Celsius

q      User settable target temperature

q      Keyboard or pull down menu options to set count-down time

q      Programmable compensation curve

q      Customized developer / paper profiles that can be saved

q      Restorable default profiles

q      User can easily switch between profiles

q      Count-down or Count-Up timing options

q      Alert sound in Count-down mode at 5 seconds prior to end

q      Multiple print / Negative processing option in count down mode


A demo version of the software and manual can be downloaded directly from Curt Palm’s website and only takes a few minutes to set up. The full version of the software can be purchased on line and will be sent to the buyer via email, or for a small fee, a CD will be mailed via USPS. Once the email with the full version arrives, it will take about 20 minutes to download the software, read the manual and set up a few developer profiles. Once the probe arrives, installation and set up is an additional 5 minutes.


Operating the program is a straightforward procedure. Prior to turning on the computer, plug the temperature probe into an available USB port. This step needs to be done prior to turning on the computer to ensure CompnTemp will recognize the probe. (With a Mac the probe only needs to be plugged in before launching CompnTemp) Once done, open the CompnTemp application and place the probe into the tray of developer. A ¼-inch insertion depth is all it needs to record the temperature accurately. An amber light on the probe will light indicating the software and probe are communicating with each other. It is important to NOT let the probe slip fully into the liquid, only the metal portion should ever touch the developer. Once the computer and probe are communicating, the amber light should go out. If you tray process film, this light should be covered with black tape as a safety precaution. Further, some laptops have illuminated logos on their covers that also need to be masked off.


CompnTemp will read the current temperature of the developer and display it in the main window of the application. Then, by using a mouse to click the start / stop button, or by pushing any key on the keyboard other than a number key, the application will begin to count. In count-up mode, the first click of the mouse starts the time and another click stops and resets the clock. It is that simple.


Another nice feature not found on any other timer is that each time a time-count is stopped (in count-up mode) or comes to an end (in count-down mode) the CompnTemp display shows both the actual Elapsed Real Time and Elapsed Comp Time. You can now know exactly how much compensation actually occurred. For example, with the pre-set Ilford compensation profile, a target temp of 68° and an actual temp of 72°, the end of a 2-minute cycle will display 1:31 Elapsed Real Time and 2:00 Elapsed Comp Time.


The main window of the CompnTemp application features large, easy to read numbers and can be customized to accommodate user preferences. CompnTemp comes with two pre-set user profiles and additional customer profiles are easy to create. The “Default” profile is equivalent to the compensating curve used in the Zone VI timer, and the “Ilford” profile is based on time/temperature compensation data provided by Ilford. The custom profile (See fig. 2) feature allows the user to create a new profile that will, for example, set a target temperature, choose number of prints / negatives per cycle (this is a nice feature as CompnTemp will beep 5 seconds -- or whatever time interval you choose -- prior to the end of the cycle and then every 5 seconds thereafter depending on the number of prints chosen when in count-down mode), choose Fahrenheit or Celsius, time type (real or compensation), change compensation curve, show option controls in the main window, change font size for main screen readouts, or count-up or count-down timing modes. As you can see, this is a very flexible tool designed to meet the unique needs of each user.


In practice setting up custom profiles is very easy and CompnTemp allows the user to create up to 5 unique profiles. For example, if you typically use Clayton P-20 diluted 1+6 for 2.5 minutes at 70F, you can create and save a custom profile that can be used at any time in the future. In addition, if you also use Dektol on occasion, a second profile can be created for that developer as well (or any other combination you can think of).


If you are using the CompnTemp timer for development of negatives, then profiles could be created for different film/developer/time combinations. The timer is most conveniently used for tray development of negatives, but it can be used for non-Jobo rotary processing by simply placing the probe into a small beaker of the developer you will pour into your processor. While not as precise as compensating off the actual developer being used, it will be more accurate than simply guessing. If you are using a Jobo processor you can just put the probe into the temperature control bath. If you use Patterson type developing tanks for roll-film, you can drill a small hole (with a #14 drill) in the plastic lid so that the probe can be inserted into the tank. (See fig. 3 and fig. 4)


When working, it is very easy to toggle between the different profiles and the software will automatically adjust to the new setting. In future releases of the software, it would be nice to see CompnTemp allow for more profiles. While 5 seems like a lot, if you use CompnTemp in count-down mode for both print and negative development then you may quickly run out of custom profiles.


We tested the CompnTemp on both PC and Mac based laptops and there were no issues with set up or operation in either Windows XP or Mac OS X. Here are a few of our thoughts:


Alan Ross


What really sets this “timer” apart is its adaptability. By taking advantage of the range of its features you can really make it your own. While the Zone VI timer was able to compensate for temperature differences and fluctuations, it was factory calibrated to a fixed 68°F target temperature – meaning that if your actual temperature was by either choice or circumstance in the 75° range the timer unavoidably counted franticly fast. With CompnTemp you can calibrate however you choose.


While many workers prefer timing in count-down mode, I have always liked count-up timers. In count-up mode I can change my mind mid-process about total developing time without having to reset anything; I can use the same timer settings or profile for an 8 minute developing time with a 5 minute fix followed by a 2 minute wash-aid simply by tapping a start-stop key. CompnTemp lets you have it your way.


Not only is CompnTemp good at what it set out to do – monitor temperature and provide accurate and customized compensation – it has also provided me with something of an education. I recently tray-processed some sheet film, and I was astonished to sit there in the dark and watch the temperature of my developer drop by 3 degrees in the course of a 15 minute process! I'd had no idea the temperature would shift so much on me – I never had any way of knowing before. The film was fine due to the compensation, but it served as quite a wake-up call and gave me cause to take steps to keep my temperatures more stable.


For hardware set-up in the Apple camp, the software installs and runs equally well on my G4 Powerbook as on my Intel based desktop Mac, and works fine with either OS 10.4 or 10.5. The Apple logo needs to be masked off on the Powerbook cover as well as with iBooks and the new MacBooks. The white-case versions of these don’t bleed any light through the plastic and can safely be used for tray processing of film. You do need to dim the display all the way down. If you use an Apple power adapter, you might also want to mask off the illuminated Charging indicator. I found it advantageous to install a special shelf to position the Powerbook in a convenient location for set-up and viewing and placed an old keyboard above the sink so that all I have to do is tap a key to start/stop the timer. This also keeps chemicals away from the computer’s own keyboard. Glow-tape helps locate the keys in the dark. (See fig. 5)


While laptops are a sensible choice for occasional use in the darkroom as a timer, there is no reason – space allowing – why any old, “outdated” computer couldn’t be set up as a permanent installation. CompnTemp is so powerful and reasonably priced that it even makes the idea of getting a used “darkroom computer” a reasonable proposal! It’s not hard to find an old iMac for around $100, and if you already have an old machine with a USB port sitting out in the garage this is a great reason to go dust it off.


Eric Biggerstaff


First of all, setting up CompnTemp and configuring the custom profiles took me about 15 minutes from start to finish on my Windows XP based laptop. The installation of both the CompnTemp software and the Go! Temp USB probe was flawless and smooth. I prefer to use timers in count-down mode so all of my profiles were set up to have the timer operate in this fashion.


I started using the application while developing film. My normal set up is to use a Jobo 3010 Expert drum on a motorized Beseler base. I use one-shot developers I mix just before use and by simply placing the temperature probe into a small cup of the developer set along side the drum , I was able to get a read out and compensated time while the Jobo drum was operating on the base. While the probe was not actually in the drum, I still feel CompnTemp was able to provide me with accurate compensation that will lead to more consistent negative development.


Next, I used the software while developing prints. Here again CompnTemp was excellent to use. I created three custom profiles for the developer / dilution / temperature / time combinations I use. While working, the application was easy to start by simply hitting the space bar on my laptop with my dry hand. The large numbers were easy to see and going from one profile to another was simple. The timer showed my target time and adjusted real time at the conclusion of each print and I had very consistent prints from start to finish.


You can purchase the CompnTemp software directly from Curt Palm at www.curtpalm.com. The cost of the software alone is $85.00 and the probe is an additional $40.00 from www.vernier.com. The software will be emailed to you once the purchase has been cleared or, for an additional fee, a CD will be mailed. Also, there are links on the website to the manufacturers of the other various recommended components so you can purchase everything needed to get started.