Originally Posted by
Neal Chaves
One of the challenges in making a good print is determining the correct exposure. The accuracy of the timer is important, as are a visible way to monitor the timing cycle and certainly an audible metronome tone on the timer. Of greater concern, is the startup characteristics of the particular light source. Fred Picker tried to address this in with several electronic devices.
The step wedge has been around for ages in the graphic arts and commercial photography industries. The Kodak (and others) Projection Print Scale was in regular use in amateur, student, military and commercial darkrooms. Because the scale was exposed for 30 seconds or one minute, the startup characteristics for the lamp are compensated for on the scale. With cold light tubes, the tube must be at a warm and stable operating temperature. A ten second burst from an cold tube could be as much as a stop and a half from that of a warm and stable tube. Even halogen bulbs have a lagging start up. A three second burst from a halogen light does not provide the same exposure as three seconds of a thirty second exposure.
I use both a Kodak Projection Print Scale (or similar) and exposure meters, on the easel and recently on the Beseler cold light head itself. When I make a test strip across a print, or section of a print, I use an audible timer with a foot switch. I make a 30 sec test strip by covering the paper completely at the start of the 30 sec timer. I uncover a new strip every three seconds. This test takes bulb characteristics into consideration. Perhaps contrast as well, because brief bursts of halogen tend to be yellow.
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