Cameras, Single Lens Reflex (SLR)

The principle of the single-lens reflex (SLR) camera, reflecting the light path by means of an angled mirror behind the lens so as to project an image onto a horizontal glass screen, dates back to the prephotographic portable camera obscura. However, the early photographic experimenters using this type of instrument soon found that the light loss inherent in the arrangement was unacceptable and adopted cameras with a direct light path.

Although the 1839 camera made by Giroux for Daguerre (the earliest photographic camera to be widely sold to the public) had a reflex viewing mirror, the first true SLR camera was patented by the Englishman, Thomas Sutton in 1861. Sutton’s camera incorporated an internal mirror that reflected the image formed by the lens up into a horizontal glass screen.

The mirror was swivelled up to cover the screen during exposure. The relative insensitivity of the wet collodion plates in use at the time and the delay imposed by the need to prepare them directly before exposure negated the great advantage of the reflex camera, continuous inspection allowing adjustment of focus. Few of Sutton’s cameras were made and the reflex principle was almost completely abandoned until ‘‘fast’’ gelatin dry plates were introduced in the 1870s.

The first SLR camera to be at all widely sold was patented by an American, Calvin Rae Smith, in 1884. Called the Monocular Duplex camera, it was fitted with an internal mirror attached to a wedgeshaped unit pierced with an aperture. Raising the unit allowed light from the lens through to a plate at the back of the camera, thus acting as a shutter.

The English company, Perken, Son and Rayment, marketed a similar camera in 1888. S. D. McKellen’s Detective camera, also sold in the U.K. during the same year, was equipped with a roller-blind shutter fitted between lens and mirror. Encapsulating the advantages of the SLR design, a contemporary review noted that an ‘‘exact and full- size picture’’ could be seen ‘‘up to the very moment of firing.’’

During the last decade of the nineteenth century, several new SLR camera designs were produced. Innovations included cameras designed to use rollfilm or magazines of cut film instead of plates, and models fitted with focal plane shutters. The ability to frame and focus moving subjects up to the moment of exposure led to several models fitted with long focus lenses being advertised as particularly suitable for naturalists or for photographing wildlife.

The most influential design of the period was the American Folmer and Schwing Graflex camera of 1898. By the standards of the day this was a compact model, the lens panel being fitted to a bellows extension moved by a rack and pinion mechanism. The English Soho Reflex camera introduced in 1905 and built to a similar pattern was immensely popular and, along with derivatives of the Graflex, was marketed until after World War II. Both types were much favored by press photographers. The amateur market was first widely exploited in the 1920s and 1930s as many relatively inexpensive rollfilm reflex cameras began to appear.

A great drawback of the early reflex camera was its bulk. Folding or collapsible models were produced from as early as 1903. Many of the best examples came from German manufacturers, perhaps the finest being the Miroflex models first produced in the late 1920s. There was a broad trend at this time towards compact all-metal cameras and a notable feature of the period was the success of precision-constructed 35 mm cameras such as the Leica and the Contax.

A 1933 reflex-mirror box attachment for the Leica camera has been described as the first application of the reflex principle to 35 mm photography. The first production 35 mm SLR camera was probably the Russian Sport camera of 1935, followed a year later by the much more influential and widely sold Kine Exakta by Ihagee of Dresden. Although basically a 35 mm version of a 127 rollfilm camera, the Kine Exakta was a well-made instrument equipped with a fast standard lens and built-in flash synchronization.

The development of 35 mm SLR cameras to the point where they displaced rangefinder models derived from the Leica and Contax as the serious photographers choice was primarily due to the introduction of the pentaprism viewfinder. For the first time, it made possible a compact reflex camera that allowed right-way-up, right-way-round, eye- level viewing. More than one pentaprism patent was filed in the 1940s but the most influential production, SLR camera with a pentaprism viewfinder was the Contax S of 1948. The Contax was soon followed by a series of 35 mm pentaprism reflex cameras produced increasingly in Japan.

From the1950s, the evolution of the 35 mm pentaprism SLR camera continued by way of a series of innovations made possible by advances in light sensor design and electronic components and circuitry. Many important features were pioneered in European cameras but were developed and refined by Japanese companies. Asahi Pentax models of the 1950s were the first widely sold SLR cameras to incorporate modern instant return mirrors and automatic diaphragms.

Similar features appeared in the modular-constructed Nikon F camera of 1959. When later equipped with through-lens metering and marketed with a wide range of lenses and accessories, the early Nikon F was arguably the most influential camera of the period. The first SLR cameras with through-lens metering (the microelectronic coupling of exposure meter to shutter and diaphragm to provide fully automatic exposure control) offered for sale to the public were again Japanese products: the Topcon RE Super of 1963, closely followed by the Pentax Spotmatic.

Since 1970, the quality camera market has been dominated by the versatile, Japanese manufactured, fully automatic, 35 mm single-lens reflex model, such as the Canon A and Nikon F series cameras. Perhaps the only exception is the square picture format camera with interchangeable film magazine exemplified by the 500C Hasselblad, favored in certain branches of professional photography.