Pentax Auto 110

The Pentax Auto 110 and Pentax Auto 110 Super are single-lens reflex cameras made by Asahi Pentax that use Kodak's 110 film cartridge. The Auto 110 was introduced with three interchangeable lenses in 1978. Three more lenses were introduced in 1981, and then the Super model was released in 1982. The camera system was sold until 1985. The complete system is sometimes known as the Pentax System 10, apparently for its official Pentax name, although most Pentax advertising only uses the camera name or Pentax-110. This model represented the only complete ultraminiature SLR system manufactured for the 110 film format, although several fixed-lens 110 SLRs were sold. The camera system also claims to be the smallest interchangeable-lens SLR system ever created.

The cameras and lenses were very small (the camera fits in the palm of a hand easily) and were made to professional SLR standards of quality.

The Pentax Auto 110 featured fully automatic exposure, with no user-settable exposure compensation or adjustments. Metering was TTL (through-the-lens) and center-weighted. Unlike 35 mm SLRs, the system's lenses did not have a built-in iris to control the aperture. Instead, an iris was mounted inside the camera body, and functioned as both an aperture control and a shutter. This mechanism was capable of programmed exposures between 1/750 s at f/13.5; and 1 s at f/2.8. To ensure that light travelling past the diaphragm blades could not get through to the film over time, the camera's mirror system also functioned as a light-tight seal when in the viewing and focusing position. Since the iris was part of the camera, all of the system's lenses had to be constructed with an f/2.8 aperture. The lens' designs, based upon the film dimensions, resulted in the 24 mm lens being the 'normal' focal length (i.e. equivalent angle of view to a 50 mm lens on a 135 format camera), while lenses of wider angles or longer focal lengths were larger.

The camera detected the film speed by the presence or absence of a ridge on the cartridge, as specified in the Kodak 110 film standard. Since there was no official specification of what the film speeds should actually be—they were just "low" and "high"—film and camera manufacturers had to decide for themselves the meaning. Pentax chose ISO 80 and 320 as their settings, but commercially available films at ISO 100 and 400 are close enough to work in practice. A film with a ISO 200 speed would result in either under-or-over-exposure. The exposure latitude of the then existing color print films was about 2 f/stops (meaning that a photographer could expose either 2 f/stops under or 2 f/stops over the exposure set by the camera). Unfortunately, some recently produced 110 film is rated at ISO 400, but is packaged with the ridge indicating "low". If this is the case, the ridge must be removed (by filing or cutting with a sharp blade) for the camera to expose correctly. Since only a few 110 cameras ever supported the ISO auto-selection, this does not affect the majority of cameras using the format but does affect the Pentax Auto 110. In 2012/2013 ISO 100 film has been produced and marketed under the Lomography label, and gives excellent results, without the need to modify the cartridge casing.

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