Journal of the Society of Motion Picture and Television Engineers (1950-1954)

scribed a modification of the standard streak-photography technique. Small reflectors such as ball bearings have been used in orthodox streak photography in a manner similar to that described above. However, a source of error in the standard streak-photographic method lies in the possible motion of the object in a direction parallel to film motion. The modified streak method of Vigness and Nowak was devised to eliminate this error, to permit measurement of large displacements and to obtain an accuracy within a few thousandths of an inch. The object photographed consists of a series of white lines an equal distance apart, marked on a dark background. These lines are in a plane perpendicular to the direction of film motion. The direction of motion of this object, rigidly attached to the part under study, should be perpendicular to the camera optical axis and to the direction of film motion. The camera lens will focus an image of these lines on the film. A cylindrical lens, on the plane surface of which is a slit parallel to the direction of object motion, is placed just before the moving film and perpendicular to its direction of motion in order to focus these lines to approximate points. Motions of the objects in a direction parallel to the film motion will not result in any displacement of the image on the film. Small rotations in a plane perpendicular to the camera's optical axis will produce second-order errors, and motions out of this plane will result in the usual scale changes in depth-of-focus problems. This technique has been used to study displacement of many inches measured to an accuracy of a few thousandths of an inch, and to 10 jusec. DuMont announced a continuously moving film camera, their Type 321, which is characterized by a 400-ft capacity of 35-mm film or paper, and a range of linear film speeds from 0.82 in./min to 15 ft/sec, in 18 fixed increments. The Lydiate Ash Laboratories in England exhibited their Type 200 continu ously moving film camera. This camera, representing a thorough and fundamental design approach, provides, through a gear box having a 60 : 1 change of speed (which can be obtained with the camera in operation), film speeds from 3 in./min to 120 in./sec. Full electronic motor control is employed. Other features are a 400-ft, 35-mm film capacity in interchangeable magazines; a built-in timing marker; provision for photographic data cards; and push-button operation through interlocking relays. A higherspeed version, providing to 40 ft /sec, has also been exhibited. An interesting French camera, a highefficiency streak camera, was described by Malan80 for studying the correlation between the optical and electrical effects of lightning strokes. The camera produced combines advantages of other previous devices such as drum recording and ease of film changing. The film remains stationary, while the optical system is mounted in a rotating drum. Beside a reflecting prism and an objective, a Wollaston prism mounted between these is given an epicyclic rotation at half the speed of rotation of the drum. This counteracts the rotation of the image around the reflected optical axis. A few modifications make this apparatus suitable for the recording of oscillograms of transient phenomena. The apparatus carries 100-ft of 35-mm film, permitting 23 successive exposures. The only adjustment necessary between exposures is the rotation of a handle which winds the film to the next unexposed position. The objective is a 50-mm,//2.8 lens, and rotation of the optical system is carried out at a speed of 510 rpm. The film exposed during photography, upon the opening of an electromagnetic shutter, is 112 cm long, and the linear speed of the image is 952 cm/sec. A technique for time and motion study was described, in an English journal,81 in which time-displacement information is recorded on a single plate. In certain time and motion study work, it is possible Kenneth Shaftan: Photographic Instrumentation in 1950 457