Today, even the simplest digital camera has a light meter that is advanced enough to calculate good exposure times for most light conditions. How different this was at the beginning of the 20th century. Photographers had to set their exposure based on their own experience, exposure tables or a best guess. Auguste-Robert Kaufmann designed the Posographe to improve this process.
Kaufmann was a businessman and passionate amateur photographer. The Posographe is an exposure calculator and its patent dates from 1922. Its development was perhaps born out of frustration. The manual says:
Determining the exposure time required to obtain a perfect negative is one of the great difficulties of photographic technique…
… when one examines the collection of the amateur photographer, one finds a considerable number of shots that are underexposed, or too bright and without detail, difficult to use. Each of these images, not to mention those that have been discarded, represents an unnecessary expense, a waste of time, and above all a very unpleasant disappointment …
The Posographe consists of a metal plate surrounded by a 13×8 cm frame. The plate is printed on both sides. One side contains the exposure input settings for outdoor photography, the other side shows the settings for indoor photography. Six metal sliders are mounted on the frame. The sliders set the exposure settings, like aperture, month, time of the day and cloudiness.
The seventh large slider is the output slider and shows the exposure time. This slider has four indicators to support multiple emulsions, including autochromes. The exposure time goes from 1/1000 sec. to 12 sec.
All sliders are mechanically connected to each other. Moving one of the input sliders shifts the output slider immediately. Moving the aperture slider from f/8 to f/16 will result in a longer exposure time. If the cloudiness is shifted from pure blue sky to dark overcast, the exposure time increases even more.
The Posographe is a clever design and was a great success. It was available in the following languages: English, German, Italian and Spanish. A special version for the Pathé Baby cinema camera was also available.
Unfortunately Kaufmann could not enjoy his invention for a very long time. He died at the age of 42 on 11 November 1927 in a car accident.
- Le Posographe d’Auguste-Robert Kaufmann – via: facebook.com