Using sunlight as a light source when printing can give unpredictable results. Wanger Lungov explains how a UV exposure meter can help when printing for example Van Dyke Brown, Cyanotype, Gum Bichromate and anthotypes.
Most of us probably started in Alternative Photography printing processes using sunlight. More than often that was in a school or community activity and just for the sake of curiosity about the chemistry, history and the artistic possibilities of the medium. Once we got serious about it, the logical next step was to procure a UV artificial light source in order to secure consistent and predictable results. That is certainly a pity because sunlight is strong, has a very rich UV spectrum and allows for any print size one can possibly dream of.
The device featured in this article, the Solar UV Exposure Meter, brings the sun back to the fore for UV printing processes. That is because is does not consider exposure in terms of counting time, but in terms o counting energy. Using it, one can make a test strip in the morning and print in the afternoon getting consistent results. If a cloud passes by, it will extend the exposure time in order to receive the preset amount of energy a print needs. Along the day, while the sun rays angle change, and the UV load also changes, the Solar UV exposure meter will make up for that and adjust the right time for each exposure.
The basic principle is that it uses a UV sensor capable of measuring continuously the UV radiation strength that is being received. The sensor is connected to a microprocessor that will be adding up small slices or packs of exposure up to the level the print maker has set in advance. When that preset is reached it beeps. The total time may change, from one print to another, according to day time and atmospheric conditions, but the UV energy the prints receives will be constant. If other variables like negative tonal range,
paper, sensitive material, development, etc are kept reasonably constant, the densities built up in the final print will be consistently predictable.
I developed and built this Exposure Meter project about one year ago. I have been using it for Van Dyke Brown, Cyanotype and Gum Bichromate, the alternative processes I normally print, and I can testify that it really solves the problem of controlling exposure with sunlight.
“I have no intention to start any business with that and, at the same time, I think it is too cool to keep it as a
secret only for my private use.”
So I prepared a complete and detailed tutorial thinking of someone with no practice or knowledge in electronics or programming. It may look complicated at first sight but believe me, it is not.
The components are found in modules ready to be assembled together. All that one has to do is to connect them, upload the sketch using a personal computer and that is it. The total cost is as low as to not be noticed by someone doing analog photography.
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