Focal Plane Shutter Research Articles

Image of Focal Plane Shutter

Image of Focal Plane Shutter

Focal-Plane Shutters and the Design of High-Frame-Rate Cameras

Operating principles for a new family of rotating-mirror framing cameras which make use of focal-plane shutters are described and examples are given. The basic concept is an extension of the idea of isotransport of image and film, presently found only in moving-film cameras. The rotating mirror and a number of prisms, plane mirrors or concave mirrors are used to produce a sequence of connected frames which move past a fixed slit in the camera at constant velocity. The moving image segments seen through the slit are then relayed to a stationary film by means of a smear camera employing the same rotating mirror. The optics of the smear camera is arranged to stop the motion of each image on the film. As a consequence, a series of stationary images which have been scanned by a focal-plane shutter in a known way are formed on the film. Use of the focal-plane shutter offers the possibility of very precise time definition. Focal-plane shutter characteristics have both advantages and disadvantages in comparison with between-the-lens shutters. One advantage is that multiple slits may be employed. If the images from several equally spaced slits are relayed to independent film areas, it is possible to increase the number of frames and the effective framing speed of a camera without increasing rotor speed or sacrificing f number. Other possible uses of multiple-slit recording are described.

A Rotating-Mirror Framing Camera with Multiple Focal-Plane Shutters

In the preceding paper by Jacobs, a new family of rotating-mirror framing cameras has been discussed. This paper describes a camera in this family in which a number of concave mirrors are used with a single rotating mirror to create a connected sequence of images which pass several slits that act as focal-plane shutters. The images seen through the slits are relayed to form separate rows of frames by means of a smear-camera arrangement. By combining 36 concave mirrors with six properly phased slits, a total of 216 frames can be recorded in approximately 1/8 revolution of a rotating mirror. The camera now being constructed at the Naval Ordnance Laboratory will use two mirrored faces, 6 by 2 in., of a rectangular rotating mirror. At the anticipated rotor speed of 600 rps approximately 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> frames/sec will be attained. Each frame will be about 0.75 in. high and 1.0 in. wide. It will be possible to vary the shutter-to-framing-time ratio from about 0.5 to about 0.02 by varying the width of the slits used in the camera. The effective aperture will remain fixed at about f/22.

A Technique for the Testing of Camera Shutters

AbstractA method of testing camera shutters is described and illustrated examples of the application of the method are given. The method is applicable to all types of shutter mechanism and uses standard laboratory equipment. Double extension or a supplementary lens is required for a full test on a focal plane shutter. The method involves photographing a trace on a cathode-ray tube screen.

Calibration of shutter speeds

A number of focal plane and central-lens shutters was tested with a specially developed simple calibrating apparatus.

A device for obtaining better detail in roentgenograms of crying infants; slit shutter radiography.

A device is described for taking sharp x-ray images of the lungs of crying and restless infants under 3 years of age. Directly before the tube opening of a condenser discharge x-ray machine a lead shutter with a transverse slit-like opening 5mm. wide is mounted to operate like a focal plane shutter. When released electrically from the control panel it falls downward 7cm. after first closing the filament and high voltage primary circuits. The exposure in any given point on the film from the resulting x-ray emission is limited by the lead shutter to between 1/200 and 1/400 of a second determined both theoretically from standard formulas and experimentally. Test films of infants' chests were made with a full wave rectified unit (0.1 sec. exposure), a condenser discharge unit (0.05 sec. exposure) and a condenser discharge unit with a slit shutter. Details in the former films were often too indistinct for clinical evaluation whereas the details in the latter were considerably better than that obtained by conventional techniques. Improved detail in chest studies and simplicity of operation of the slit shutter should be of value in clinical and experimental medicine.

A Step-Sector for the Astigmatic Spectrograph

A step sector is described which can be used with astigmatic spectrographs to give results in every way as good as those obtained with conventional sectors and stigmatic instruments. In its action it may be described as a cross between a focal plane shutter and a band saw, as it consists of a continuous band of opaque film with a succession of stepped openings cut from its center. This film is passed at high speed in front of the focal curve next to the sensitive emulsion, then around a return path which is not in the optical path of the instrument. Added versatility is achieved by the inclusion of adjustable vertical and horizontal masks.

A 100,000,000 Frame per Second Camera

Shock waves close to the edge of explosive charges have been successfully photographed at rates exceeding 100,000,000 frames/sec. These ultra high framing rates are obtained with a multi-slit focal plane shutter which is transported optically across the film plane by a rotating mirror. Linear shutter speeds up to 3,000 meters/sec are easily obtained, and the resulting framing rates with the proper selection of slit widths can be varied from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> frames/sec. Each individual frame is composed of a series of lines, and the degree of “discontinuity” across each frame is proportional to the total number of frames.

A 100,000,000-frame-per-second camera.

Shock waves close to the edge of explosive charges have been successfully photographed at rates exceeding 100,000,000 frames per second. These ultra-high framing rates are obtained with a multislit focal plane shutter which is transported optically across the film plane by a rotating mirror. Linear shutter speeds up to 3000 meters per second are easily obtained, and the resulting framing rates with the proper selection of slit widths can be varied from 105 to 109 frames per second. Each individual frame is composed of a series of lines, and the degree of ``discontinuity'' across each frame is proportional to the total number of frames.

Camera Shutters*

An extensive program of research into characteristics of shutters, begun in 1941, has resulted in a series of definitions and test methods for between-lens and focal-plane type shutters which have been adopted by the ASA. The characteristics of these two types of shutters, and of louvre shutters, are reviewed, and the important distinction between effective exposure time and actual (or motion-stopping) exposure time in these two shutter types is clarified. The oscillographic test method for between-lens shutters is described and depicted via photograph and schematic diagram. The strobotac and drum tester method for focal plane shutters are summarized, as is a method for testing louvre shutters.The effect of inefficient between-lens shutters on optical performance, effect of a glass pressure plate on efficiency of focal-plane shutters, and equations for the two types of distortion caused by focal plane shutters are discussed. The utilization and advantage of shutter speed in aerial cameras to reduce the deteriorative effects upon definition caused by forward aircraft speed, angular motion of the aircraft about its axis, and camera vibration are discussed.The shutterless strip camera and the corollary principle of image speed compensation with moving-film magazines in conventional cameras, and the potentialities of this important new development, are described.The impetus of wartime necessity resulted in development of several new shutters, improvements in others, and consideration of many more types. The Langer multiple-slit focal plane shutter, shutters based on birefringent phenomena, multiple-disk between-lens shutters are considered. Shutter leaves of Be-Al alloy were tried, with conspicuous success. The work done by Mitchell in doubling the speed of the 6-in. K-17 shutter and a detailed analysis of research results obtained in improving the K-22 focal plane shutter are presented.A louvre-shutter for the 48-in. f:6.3×18 lens was built at the Photographic Laboratory. Photographs and a schematic diagram of this high performance shutter are included. A doctrine of tactical usage and development for shutters has been formulated; mapping cameras will continue to use between-lens shutters, as will night cameras, but the very large day reconnaissance camera will use focal plane shutters exclusively. A list of seventeen memorandum reports, which cover in detail the work summarized in this paper, is appended.

A new method for adjusting synchronizers, also suitable for testing focal-plane shutters

Description of a method for adjusting synchronizers for photoflash lamps with the aid of a falling-plate oscillograph (lending itself to self-construction), both for Compur and focal-plane shutters and, if desired, without spending flash lamps. The apparatus is also suitable for testing focal-plane shutters.

Testing focal plane shutters

A method is worked out for measuring with the aid of a cathode-ray tube the course of either of the blinds of a focal plane shutter as a function of the time. The exposure time and the efficiency can be deduced from the results found.

The British Journal Photographic Almanac and Photographer's Daily Companion: with which is incorporated “The Year-Book of Photography and Amateur's Guide” and “The Photographic Annual”, 1924

THIS well-known publication preserves its characteristic features. The list of photographic societies, camera clubs, and the like, gives the names and addresses of the acting officers of well over 500 of such bodies, all except 50 or so belonging to Great Britain. There are also a few professional societies in a separate list. The article by the editor, which takes the place of the multitude of contributions from a great many workers that characterised the Almanac years ago, is “On Using a Hand-Camera.” He exposes the fallacy that a focal plane-shutter is of necessity very efficient, and gives the practical efficiency as varying between 50 and 99 per cent., according to circumstances. He says that the picture given by a finder that consists of a small lens and a ground-glass screen is dim, but he does not add that this practical difficulty may be quite overcome by putting the 45° mirror outside instead of inside the finder. The tables and formulae are probably the most used part of the book, and some of them have been revised and improved. May we point out (p. 451) that “a 2d. tin of Globe polish “has not been obtainable for some years, and that the contents of the present small tins are not what they were? We are glad to see such firms as Zeiss, Goerz, and Hauff represented again among the advertisements.

Notes on photographic shutter testing

The paper briefly describes a number of the more important methods of measuring shutter speeds and in particular the method employed at the National Physical Laboratory. Details of a number of recent modifications are given and a method for determining data connected with the motion of the blind of a focal plane shutter is described.