The rapatronic camera (a portmanteau of ''rap''id ''a''ction elec''tronic'') is a

high-speed camera A high-speed camera is a device capable of capturing moving images with exposures of less than second or frame rates in excess of 250 frames per second. It is used for recording fast-moving objects as photographic images onto a storage medium ...

capable of recording a still image with an exposure time as brief as 10

nanosecond A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or seconds. The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit (e ...

s. The camera was developed by

Harold Edgerton Harold Eugene "Doc" Edgerton (April 6, 1903 – January 4, 1990), also known as Papa Flash, was an American scientist and researcher, a professor of electrical engineering at the Massachusetts Institute of Technology. He is largely credited with ...

in the 1940s and was first used to photograph the rapidly changing matter in

nuclear explosion A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, th ...

s within

millisecond A millisecond (from '' milli-'' and second; symbol: ms) is a unit of time in the International System of Units equal to one thousandth (0.001 or 10−3 or 1/1000) of a second or 1000 microseconds. A millisecond is to one second, as one second i ...

s of detonation, using exposures of several microseconds. To overcome the speed limitation of a conventional camera's mechanical shutter, the rapatronic camera uses two polarizing filters and a Faraday cell (or in some variants a

Kerr cell The Kerr effect, also called the quadratic electro-optic (QEO) effect, is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index chang ...

). The two filters are mounted with their polarization angles at 90° to each other, to block all incoming light. The Faraday cell sits between the filters and changes the polarization plane of light passing through it depending on the level of magnetic field applied, acting as a shutter when it is energized at the right time for a very short amount of time, allowing the film to be properly exposed. In magneto-optical shutters, the active material of the Faraday cell (e.g., dense

flint glass Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractiv ...

, which reacts well to a strong magnetic field) is located inside an

electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire (likely copper) wound into a electromagnetic coil, coil. A current through the wire creates a magnetic ...

coil, formed by a few loops of thick wire. The coil is powered from a pulse forming network by discharging a high-voltage capacitor (e.g., 2 microfarads at 1000 volts), into the coil via a

trigatron A trigatron is a type of triggerable spark gap switch designed for high current and high voltage (usually 10–100 kV and 20–100 kA, though devices in the mega-ampere range exist as well). It has very simple construction and in many cases is the ...

or a

thyratron A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, pro ...

switch. In electro-optical shutters, the active material is a liquid, typically

nitrobenzene Nitrobenzene is an aromatic nitro compound and the simplest of the nitrobenzenes, with the chemical formula C6H5 NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced ...

, located in a cell between two electrodes. A brief impulse of high voltage is applied to rotate the polarization of the passing light. For a

film A film, also known as a movie or motion picture, is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are generally, sinc ...

-like sequence of high-speed photographs, as used in the photography of nuclear and thermonuclear tests, arrays of up to 12 cameras were deployed, with each camera carefully timed to record sequentially. Each camera was capable of recording only one exposure on a single sheet of film. Therefore, in order to create

slow motion Slow motion (commonly abbreviated as slow-mo or slo-mo) is an effect in film-making whereby time appears to be slowed down. It was invented by the Austrian priest August Musger in the early 20th century. This can be accomplished through the use ...

images, banks of four to ten cameras were set up to take photos in rapid succession. The average exposure time used was a single microsecond.

References

External links

{{Commons, Photos taken with Rapatronic cameras
Rapatronic Shutter
technique description at the Edgerton Digital Collections website
MIT Museum Collections
- Rapatronic camera with magneto-optic shutter, type CA-1 High-speed cameras

See also

References

External links