Single Lens Reflex Camera

Single Lens Reflex Camera

  • Probably the most widely used type of camera today is the single-lens reflex (SLR). Most single-lens reflex cameras use 35 mm film, but several popular makes use 21/4 inch film sizes, and a few use 4 x 5 or even 5 x 7 inch film sizes. The single-lens reflex camera is so called because the lens used to make the picture also serves, through the interposition of a moving mirror, as rangefinder and viewfinder system. When a scene is viewed and brought into focus, the light from the lens is directed to a viewing screen by the mirror, and from there to the eye by way of the prism. The prism reverses the image reflected from the mirror into the correct left-right configuration, and allows eye-level viewing as well.

  • In modern single-lens reflex cameras, pressing the shutter release sets off a train of mechanical activity: the mirror swings up out of the light path and the focal plane shutter opens, which allows the image to be recorded on the film. In most modern designs, the iris diaphragm in the lens mount is "set" at the desired opening prior to focusing but actually remains wide open until the shutter release is pressed. Then, just before the shutter opens, the iris automatically closes down to the chosen setting for the duration of the exposure. In most cameras, the mirror comes back down and the iris reopens automatically as soon as the shutter closes, to restore viewing at once. Thus, direct viewing of the subject is interrupted only for a split second longer than the duration of exposure, allowing virtually constant monitoring of subject activities. Although single-lens reflex cameras have the most complicated mechanical design of any common camera type, nearly all of them are remarkably dependable.

  • They are also highly versatile. Since viewing and picture making are accomplished with the same lens, there is no parallax problem. Extreme close-up and very long telephoto photography are readily accomplished and there is wide interchangeability of lenses. Meanwhile, the basic camera approaches the rangefinder camera's small size, lightness, and speed of operation (indeed, most 35 mm versions have a small variation of the split-image rangefinder built into the viewing screen to speed up and assist focusing). Some manufacturers have recently introduced unusually small and compact 35 mm SLR models, and a general trend toward smaller size is now apparent. SLRs using films as small as the 110 size are available, including models with interchangeable lenses.

  • As for disadvantages, the single-lens reflex design is slightly more conspicuous in use owing to the combined noise of the focal plane shutter and the moving mirror, and in a few very critical uses "mirror-flop" can introduce unwelcome vibrations. (These latter will be most detectable if slow shutter speeds are being combined with high magnification, as with extreme telephoto photography.) In a few SLRs the mirror can be manually locked up out of the path of light prior to exposure to avoid the problem. This is useful when the subject is motionless.

  • Single-lens reflex cameras using 35 mm or smaller films share with 35 mm rangefinder cameras the disadvantage of small film size. However, the better designs partially compensate for this by very exact framing characteristics, which allow absolutely full use of the available film area, an essential feature if color slides for any critical or important use are to be made.

  • The special subject areas in which the 35 mm single-lens reflex camera excels are photojournalism and nature photography of small, live, moving objects, such as insects. As an indication of the popularity and versatility of single-lens reflex cameras, approximately 90% of all photojournalists now use this type of instrument-as does probably a similar percentage of all serious photographers.

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