Buscaron Photography

Photography at exposure durations shorter than those possible with conventional shutters or at frequencies (frame rates) greater than those achievable with motion picture cameras with intermittent film movements is useful in a wide range of technical applications.

The best conventional between-the-lens shutters rarely yield exposures shorter than 1/500 s. Some focal plane shutters are rated at 1/2000 or 1/4000 s but may take 1/100 s to traverse the film format. Substantially shorter exposures are possible with magnetooptical shutters (using the Faraday effect), with electrooptical shutters (using the Kerr effect), or with pulsed electron image tubes. Alternatively, a capping shutter may be used in combination with various pulsed light sources which provide intense illumination for very short durations, including pulsed xenon arcs (electronic flash), electric arcs, exploding wires, pulsed lasers, and argon flash bombs. Flash durations ranging from 1 millisecond to less than 1 nanosecond are possible. Similarly, high-speed radiographs have been made by discharging a short-duration high-potential electrical pulse through the x-ray tube. See also Faraday effect; Kerr effect; Laser; Stroboscopic photography.

The classical foundation for serial frame separation is the motion picture camera. Intermittent movement of the film in such cameras is usually limited to 128 frames/s (standard rates are 16 and 24). For higher rates (up to 10,000 frames/s or more) continuous film movement is combined with optical compensation, as with a rotating plane-parallel glass block, to avoid image smear. Pictures made at these frequencies but projected at normal rates slow down (stretch) the motion according to the ratio of taking and projection rates. Higher rates, up to 107 frames/s, have been achieved with a variety of ingenious special-purpose cameras. In some, the sequence of photographs is obtained with a rapidly rotating mirror at the center of an arcuate array of lenses, and a stationary strip of film. In others, the optics are stationary and the film strip is moved at high speed by mounting it around the outside or inside of a rapidly rotating cylinder. To overcome mechanical limitations on the rotation of mirrors or cylindrical film holders at high speeds, image dissection methods have been employed, that is, an image is split into slender sections and rearranged to fill a narrow slit at the film. The image is unscrambled by printing back through the dissecting optics.