Physiogram techniques

I took the pictures. Peter Hunt conceived and constructed the pendulum. Most things were a joint effort.

Film processing

The camera was a basic 35mm camera, without rangefinder, exposure meter, or interchangeable lenses. Most of the photographs were taken at f/4.

For the first few sessions, normal 35mm black-and-white film was used. This was very inconvenient, because complicated physiograms are very unpredictable, and opportunities were missed in the hours before the film was processed.

Another inconvenience was having to work in the dark. With the camera swinging, it is tricky to get the light and the camera swinging satisfactorily, then open the shutter on a moving camera! Covering the open lens of the camera until it was time to record the trace ran the risk of premature exposure.

I resolved both of these problems in later sessions by using Orthochromatic 35mm film. This was insensitive to red light, so we were able to work in normal darkroom conditions using a safelight. And it could be processed like print film. Used in 2-inch lengths, a trace could be recorded, and the result developed and stopped, so that we could see the result within about 3 minutes. (It wasn't necessary to fix it before checking the results. That was done afterwards).

Any adjustments could be made and a new trace recorded within minutes. Some of the most adventurous physiograms were made by this method.

Swinging the light and the camera

When both the camera and the light source are moving, there is the problem of how to provide sufficient flexibility in the ratios of the periods of swing, (of camera and light), to generate all attractive combinations. We couldn't do everything we wanted with a conventional pendulum.

We therefore used a compound pendulum. This was a rigid pendulum, pivoted near the middle, with the top half in the loft. By adjusting the positions of the weights, the period could range from nearly that of a normal pendulum, to "very large".

Swinging the camera was easier. We used a wooden platform, with parallel cords from each corner to the ceiling. The reason for making the cords parallel was to ensure that the camera continued to point vertically upward throughout its swing. This reduced the complications of the image, enabling the results to be more predictable.