Photographic Techniques

B

Digital Photography

In the late 20th century, new technologies began to blur the lines between photography and other image-making systems. In some new forms of still photography, silver-halide emulsions were replaced by electronic methods of recording visual information. In 1981, the Sony Corporation introduced its still video camera the Mavica, based on an earlier industrial model, the ProMavica. Unlike the conventional video camera, which used magnetic tape, the Mavica recorded visual data—light reflected from objects in the scene photographed—on a floppy disk. The images were viewed on a monitor connected to the Mavica's playback unit. Canon also entered the still-video-camera market. Its RC-470 camera required a still video player for viewing, but the Xap Shot, which recorded 50 still images, with 300 to 400 lines of resolution, on a 5-cm (2-in) floppy disk, did not require any special equipment. It could be connected directly to a television receiver. Paper prints of the recorded images could also be made, using a laser-driver computer printer.

Digitization of photographic images began to revolutionize professional photography, giving rise to a specialized field known as image processing. Digitization of the visual data in a photograph (that is, conversion of the data into binary numbers using a computer) made it possible to manipulate the photographic image by means of specially developed computer programs. In the 1980s, the Scitex image-processing system enabled the user to move or erase elements in a photograph, change colours, fashion composite images from several photographs, and adjust contrast or sharpness. Adobe’s Photoshop application further refined these capabilities, becoming the standard image-editing tool of the print and Web design industries in the 1990s.

As the quality of digital imaging technology improves, digital photography has begun to replace conventional photographic technology, both professionally, in areas such as photojournalism, and among amateur enthusiasts. Digital cameras utilize a light-sensitive chip for image capture called a CCD (charge-coupled device), which is made up of sensors that gather colour and light information. This information is then converted into digital data—pixels. In a high-resolution, full-colour photograph taken with the digital equivalent of a professional 35-mm SLR camera, there will be as many as several million pixels. Some digital cameras are able to transfer their large picture files directly into a computer for storage. Others accept a disk or similar portable storage unit to achieve the same purpose. The original high-resolution image can later be reproduced in ink (in a magazine, for example) or as a conventional silver halide print.

Digital cameras aimed at the amateur photography market function much as point-and-shoot cameras do, with automatic focus, automatic exposure, and built-in electronic flash. Pictures from these cameras contain fewer pixels than those from a more expensive camera and are therefore not as sharp. After taking pictures, image files can be transferred to a home computer, stored on disk, or sent via e-mail.

VI

Special Techniques

By the end of the 19th century, photography was already playing an important specialized role in astronomy. Since that time, many special photographic techniques have been developed; they serve as important tools in a number of scientific and technological areas.

A

High-Speed Photography and Cinematography

Most modern cameras allow exposures with shutter speeds of up to 1/1,000 second. Shorter exposure times can be attained by illuminating the object with a short light flash. In 1931 the American engineer Harold E. Edgerton developed an electronic strobe light with which he produced flashes of 1/500,000 second, enabling him to photograph a bullet in flight. By the use of a series of flashes, the progressive stages of objects in motion, such as a flying bird, can be recorded on the same piece of film. Synchronization of the flash and the moving object is achieved by using a photocell to trigger the strobe light. The photocell is set up so that it is illuminated by a beam of light that is interrupted by the fast-moving object as soon as the object comes into the field of the camera.

More recently, high-speed electro-optical and magneto-optical shutters have been developed that allow exposure times of up to a few billionths of a second. Both types of shutter make use of the fact that the polarization plane of polarized light in certain materials is rotated under the influence of an electric or magnetic field. The magneto-optical shutter is made up of a glass cylinder placed inside a coil. A polarization filter is placed at each side of the glass cylinder. Both filters are crossed, and light that passes through the first filter becomes polarized and is stopped by the second filter. If a short electric pulse is passed through the coil, the polarization plane of the light in the glass cylinder is rotated, and light can pass through the system.

The electro-optical shutter, built in a similar way, consists of a cell with two electrodes that is filled with nitrobenzene and is placed between the two crossed polarization filters. The polarization plane inside the liquid is rotated by a short electrical pulse at the electrodes. Electro-optical shutters have been used to photograph the sequence of events during the explosion of an atomic bomb.

Very fast motion can also be studied by high-speed cinematography. Conventional techniques, in which individual still photographs are taken in a fast sequence, allow a maximum rate of 500 frames per second. By keeping the film stationary and using a fast rotating mirror (up to 5,000 revolutions per second) that moves the images in a sequential order over the film, rates of a million pictures per second can be attained. For extremely high rates, such as a billion pictures per second, classical optical methods are abandoned and cathode ray tubes are used to make the exposures.

B

Aerial Photography

Special cameras are often equipped with several lenses and large film magazines and set in vibration-free mountings on aeroplanes. They are used in extensive land surveys for map-making, for studying the growth of cities for town planning, for detecting traces left by ancient civilizations, and for observing land use and the distribution of animal populations and vegetation. Cameras mounted in satellites are also used for such photography. A special application of aerial photography is military surveillance and reconnaissance; some reconnaissance satellites are equipped with cameras having objectives of long focal lengths that produce images, of very high resolution, on which cars, or even smaller objects, can be recognized. Advanced satellite photographic methods, which until recently were used almost exclusively by military, intelligence, and weather agencies, are increasingly being employed by geologists to uncover mineral resources and by news organizations to obtain instantaneous photographs of distant news events.

C

Underwater Photography

Underwater cameras require a watertight housing with a glass or plastic window in front of the lens. Usually, during daytime, photographs can be taken at depths of up to 10 m (more than 30 ft). Greater depths require artificial light, such as an electronic flash or floodlight. The quality of the photographs depends on the clarity of the water; in water full of particles, the light reflected from the particles renders anything but close-ups impractical. Underwater photographers often use wide-angle lenses to compensate for the effect that anything under water appears 25 per cent closer than it is in reality, because the refractive index of water is greater than that of air. Recording the beauty of the underwater world with the camera is a popular activity of scuba-diving enthusiasts. Special underwater cameras in pressure-resistant housings are also used in deep-sea exploration.