fine art black and white photography, black and white prints

Reference: Materials and Equipment: RHDesigns Stop Clock Vario


The RHDesigns Stop Clock Vario is the only major darkroom item that I purchased new. I was previously using a Gralab digital timer, but I was intrigued when I came upon the idea of F-stop timing devices for the darkroom. Now, I do not have exorbitant amounts of money to spend on darkroom equipment, but after researching thoroughly I felt that this was a well deserved expenditure. Below are a few of the things worth noting, more info can be found at their website listed above.



F-stop Timing - essentially the same thing you have been using on your camera all this time. Most darkroom timers work in standard second intervals, but imagine trying to use you camera with the same type of shutter speeds; it would be cumbersome and there would be a lot of unnecessary values in the range. Photo paper uses an emulsion just like film, and it responds to light in the same way. Doubling the amount of light will increase the print (or negative) value by one stop (although in an opposite direction, of course). Most experienced darkroom printers use a rough F-stop timing for their initial test strips (something like: 4, 8, 16, 32 seconds, these are 1 stop intervals). What this timer does is allow you to print using the F-stop method quite easily and as accurately as 1/24 increments. F-stop printing allows the user to translate all that they intuitively know about the Zone System in the field to the printing stage of the process. An F-Stop printing chart will help to explain this idea by example.

Cold Light Sensor - This is the only real difference between the Vario model and the Professional model. Cold lights fluctuate in light intensity with temperature, and this can cause problems for repeatability. This sensor alleviates the problem. It has a lead that attaches to the sensor in a cold light head and adjusts the rate of the exposure based on the intensity of the light. The professional model does not have this feature, but it can be hooked up to their ZoneMaster II exposure meter.

Dry Down Compensation - All papers "dry-down" to some extent, particularly fiber papers. Most papers darken 8-12%. This is often the cause of muddy prints, when you remember them looking so bright in the darkroom. Following a simple test for the amount of dry down in your particular process, you simply program the timer with the amount of dry down necessary. When you are happy with the values in your wet print looks, hit the dry down compensation button and it will reduce the amount of exposure appropriately.

Print Program Memory - The meter allows you to program in the separate burn areas of the print and will adjust them accordingly as you change the base exposure.

Test Strip Function - This is probably the best "extra" feature of the timer. To run a test strip, simply decide on an initial base exposure, decide on the increment (I usually use 1/4stop to start), and hit the foot pedal. Then cover the print in small increments and keep stepping on the pedal. The test strip is always a perfect gradation. This is a wonderful time saver.

This is a very well made device and RHDesigns is very supportive with technical issues. For example, I could not get the light sensor on my unit to work in accordance with my Zone VI cold light head. I called RHDesigns and they said that the wires may need to be switched. I cut and re-soldered the wires in the sensor lead as they mentioned and indeed the timer now recognized the sensor. However, the sensor was not responding to the light levels. I now believe that my sensor is bad, but I have not had a chance to replace it yet. I would by another RHDesigns timer instantly if I ever needed one.


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All images Copyright Todd Schoenbaum 2005