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Chronophotography - Muybridge’s Experiments, Marey’s Single Negative, Other Systems, Present Day Use, Digital Techniques

subject frame action camera

ANDREW DAVIDHAZY
Rochester Institute of Technology

Chronophotography, as its name suggests, is the photographic capture of movement over time by means of a series of still pictures, which are usually combined into a single photograph for subsequent analysis. This differs from cinematography in that the final result is a single photograph comprising a series of still images that can be studied at leisure, without the complex projection equipment needed for motion pictures.

Muybridge’s Experiments

Among the first applications of chronophotography were the investigations conducted in Paris by Professor J. Marey around 1870, which related human and animal motion by means of various mechanical devices. He called the photographic records chronographs. An American racehorse owner, Governor Leland Stanford of California, doubted the results of some of Marey’s investigations into the locomotion of racehorses—in particular the hypothesis that there was one instant when a trotting horse had all of its feet off the ground simultaneously. E. J. Muybridge, an English photographer living in San Francisco, was commissioned to confirm Marey’s findings.

In 1877, Muybridge succeeded in proving that Marey was right, and in doing so produced what was the first true chronophotograph. These classic pictures were made by arranging for a horse and rider to pass in front of a row of cameras with shutter releases connected to threads stretched at regular intervals across the path. As the horse came opposite each camera in turn, it broke the thread operating that particular shutter and took its own photograph. The series of photographs, when printed on one sheet of photographic paper, yielded a continuous chronophotograph.

In 1880 Muybridge devised a projection instrument, which he called zoopraxiscope, to demonstrate the movement. Between 1884 and 1885 he extended his chronophotography to the movement of a great variety of animals and humans. In this series he used up to 36 cameras with shutters electrically operated by a clockwork device.

Marey’s Single Negative

Muybridge’s experiments prompted Professor Marey to adopt the photographic approach to his own research and experiments. He constructed various cameras designed to record the whole series of chronophotographs on the one negative. His first apparatus, constructed in 1882, consisted of a plate camera equipped with a spring motor-driven rotary disc shutter with a number of regularly spaced apertures. As each aperture passed in front of the plate, it recorded the position at that instant of an object moving across the field of the camera. A small object moving quickly recorded a series of separate images on the plate, the space between depending on how fast the shutter was rotated.

If the subject was large in relation to the speed or rotation of the shutter, the successive images overlapped and gave a confused picture. Marey overcame this difficulty by putting his subject into a black suit with a white strip sewn down the arm and leg facing the camera. He then took the photographs against a black background and obtained a series of separate images of the white stripes. This way he was able to produce records of the movements of the limbs of people walking or running past the camera.

Marey’s next development was a “gun” that took a series of pictures of a moving subject and recorded them separately on a single plate. The gun carried a circular plate in front of which was a disc with 12 openings around its circumference. In front of this disc was a second disc pierced with a slit. On pressing the trigger of the gun, a clockwork mechanism rotated the discs. The disc carrying the 12 frames rotated 1/12 of a revolution while the disc carrying the shutter slit revolved once, so that each of the 12 openings appeared in turn behind the lens and was exposed through the slit. The result was a plate carrying 12 separate photographs showing successive attitudes of the moving subject. This gun successfully recorded chronophotographs of birds in flight, taking 12 successive pictures per second with a shutter speed of 1/720 second.

In 1883 the French government established a department of physiological research in Paris, where Marey carried on chronophotographic investigation of the movements used by humans and animals in various forms of activity. Marey subsequently recorded chronophotographic sequences on long rolls of paper and finally, roll film and in 1892 was able to project them.

All of his instruments for this study suffered from an inherent disadvantage: The sensitized material had to be transported fast enough to separate the image and brought to a sudden stop at each instant of exposure. In practice this meant being restricted to very small images to reduce the amount of shift of the material between each exposure. This type of record could be useful only if the individual pictures were large enough to be examined in detail, because the sensitized materials of the time would not permit a high degree of enlargement. For this reason a number of workers in this field chose to develop the Muybridge approach of making the successive exposures in a number of separate cameras.

Other Systems

The apparatus used by General Sebert in 1890 consisted of six full-sized cameras mounted in a circle with an electric motor in the center. The motor carried an arm that rotated and operated the shutters of each camera in turn. This arrangement was used for photographing projectiles.

A year or two after this, Albert Londe constructed a camera in which sets of lenses equipped with electromagnetic shutters formed separate images regularly arranged to occupy a single plate. One six-lens camera used a 13 × 18cm plate, while one with 12 lenses covered a 24 × 30cm plate. In these cameras, there was a separate clockwork selector switch, governed by a metronome that operated each of the shutter solenoids in turn, allowing a variable time interval between the successive exposures according to the speed and range of the action to be analyzed.

In the mid-1880s, O. Anschutz, working in a parallel direction to Muybridge, constructed and used chronophotographic arrangements of up to 20 cameras. Like Muybridge, he devised a method of reproducing the movement from his results. He mounted his pictures on a drum that could be rotated to bring each picture in turn into a viewing aperture. As each picture came into view, it was illuminated by an electric spark so that as the drum rotated, the observer saw a moving picture.

Present Day Use

Researchers in other countries have also been interested in depicting movement by means of chronophotographs, but, although chronophotography was directly responsible for the development of cinematography, it pursued its own distinct course right up to the present time. There is a basic difference between these two methods of photography. In both, a series of still pictures for detailed study is recorded, each picture freezing a particular phase of the action. In cinematography the object will produce a moving picture of the entire event, while in chronophotography the image is stationary, but captures its motion.

The still pictures taken in chronophotography are usually of a larger format and of a higher standard of definition than a motion picture would be. Today some of the most important applications of chronophotography are in time-and-motion study.

A special type of chronophotography that is reminiscent of Marey’s early apparatus is carried out today with electronic flashes operating as stroboscopic light sources. The subject moves against a dark background and is illuminated by an intermittent flash while the camera shutter is left open. This produces a succession of images on the same frame, each image displaced both in time and space from the preceding one by an amount that depends on the frequency of the flashes and the speed of the movement.

Chronophotographs can also be made on a single sheet of film with the moving subject remaining essentially in the same general location over time. In this manner H. E. Edgerton, in the mid-1900s, produced a significant body of work examining the motion of athletes, most notably golfers and tennis players, and various animals.

These photographs typically can only record action over a short period of time because the sequence of exposures interferes with images recorded earlier in the action. To overcome this limitation, photographers have swung the camera while recording the action, but this calls for very large dark studios, and the length of time available for recording motion is limited by the time it takes the subject to traverse from one side of the viewfinder to the other.

A variation on this approach, but one that is also a true chronophotograph, involves moving the film while the action, illuminated by a stroboscopic flash, takes place in a restricted location in space against a dark background. The duration of the event that is studied now can be much longer, extending easily into tens of seconds of several minutes at usual sampling, or flashing, rates of 10 flashes per second or so.

Because of the short duration of the flash, it is possible to analyze extremely rapid motion, while movements of a dancer or athlete photographed in this way can produce scientifically informative and artistically beautiful images.

Digital Techniques

The arrival of digital imaging has offered several new possibilities for chronophotography. A unique digital technique for generating chronographs came about with the introduction of a “frame store” instrument that stores changing image information within successive frames captured at various rates by a conventional video camera. The device would store only information from consecutive frames that was either of a higher or lower value than that preset within the memory device. If one chose a dark background to begin with and the subject everywhere reflected more light than the level for which the system was set, then as long as the subject remained stationary it would simply rise to some level due to the lighting present and stay there no matter how long the exposure. However, if parts of the subject, or the whole subject, moved between frames, the memory device would keep the initial stationary image on the screen but show where the moving subject’s parts were at a later time. Unlike a film record the device does not “overexpose” stationary parts of a subject because exposure is not cumulative, but is rather a visual representation of a particular level during the exposure time associated with a single frame.

A further development in chronophotography came about with the advent of digital imaging technology and the application of computer programs or software to the production of images that mimic traditional techniques, which are also possible to duplicate with conventional digital still cameras.

Most of the software-based digital techniques rely on the capture of a record of a subject’s motion typically based on the use of a traditional motion picture camera or other motion capture device such as a camcorder, firmly affixed to a tripod. Each frame of a short action sequence captured at speeds of 15, 30, or 60 frames per second is digitized (if original is “analog”) and subsequently The digitized frames comprising the action are then examined and those where the action appears to visually connect from one frame to the other are extracted and stored. One might select every frame or every "n"th frame depending on how many frames can be practically used to describe a brief action, such as that of a skier completing a jump. A frame without any action is used as the reference frame, and the image of the subject in action is extracted from each frame (and stored) based on the fact that each frame remains the same from frame to frame except where the subject covers a different area of the frame. This is done for all the frames in the sequence. They can then be pasted one after the other in their proper place within the original frame that did not include any action. The images are often “cleaned up” for small imperfections. Software that almost completely automates the whole process of assembling a chronographic record is now available.

The big advantage of chronophotographic assembly based on this digital approach is that unlike stroboscopy, it is possible to show events in full daylight if needed. There is no danger of “overexposing” the background. The shutters of digital motion cameras can also be adjusted for very brief exposure times to keep blurring of most moving images within acceptable limits.

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