Paul Wainwright

Bell Telephone Laboratories, Retired
Atkinson, New Hampshire, USA

The Blackburn pendulum is a common textbook exercise that is familiar to any student of physics, but as a senior in high school in 1967 I saw it as an artistic tool. I proceeded to make a number of simple time exposure photographs, looking up at a small neon bulb attached to such a pendulum.

For the past 8 years I have used a 3-meter Blackburn pendulum in my barn with an LED, and my camera is a large-format 4 x 5 inch sheet film camera. Working at night in total darkness, the camera looks straight up, and a time exposure is made as the LED traces out the pendulum’s path. Since a Blackburn pendulum approximates two harmonic oscillators, I name my images according to the musical harmonic interval they depict.

Pendulum Light Painting 152S: Major Sixth Harmonic Interval
Pendulum Light Painting 152S: Major Sixth Harmonic Interval
40 x 50 cm
Archival silver gelatin photographic print from 4 x 5 inch negative

Photographic light painting of an LED attached to a Blackburn pendulum strung to produce orthogonal periods of motion in a 5-to-3 ratio (a major sixth harmonic interval). Total exposure time was 5 min 37 sec. The exposure was started in the upper left corner of the image, and the camera was motionless throughout the exposure. Unlike image 165J, the brightness of this image is modulated not by changing the brightness of the LED but by the resonance effect as the amplitudes decrease.