Half-frame camera
A half-frame camera is a camera using a film format at half the usual exposure format. A common variety is the 18×24 mm format on regular 135 film. It is the normal exposure format on 35mm movie cameras. For still cameras using the 35mm film, the usual format is 24×36 mm, so still cameras taking 18×24 mm exposures are called half-frame cameras. There was a vogue of half-frame cameras in the 1960s, mainly from Japan, originating with the Olympus Pen models. It allowed for a very compact camera, using commonly available film , unlike other subminiatures that used exotic films (16mm, 9.3mm, etc.). This vogue ended when cameras like the Rollei 35 or the Olympus XA showed that it was possible to make cameras as small as the half-frame ones, but taking 24×36 mm exposures. A half-frame camera fits twice as many photos on to a standard roll of film. For example 72 exposures on a 36-exposure roll, 40 on a 20-exposure roll, and so on. Color film was expensive during the heyday of the half-frame camera, and the use of half-frame saved money. The  exposures have a vertical (portrait) orientation as opposed to the horizontal (landscape) orientation of a 35mm SLR or rangefinder, with the exception of cameras whose film mechanisms run vertically (examples include the Konica Recorder and Belomo Agat 18). The most advanced half-frame camera that was designed as such from the start is the Yashica Samurai single lens reflex. For some specific needs, there were cameras originally designed for full-frame pictures that were produced or custom modified in very small series as half-frame models, for example some Leica (1950 made in Canada Leica 72), Nikon (1960-61  Nikon S3M 18x24mm rangefinder) or Robot (Robot 24x24mm camera) rangefinders, and some Alpa (Alpa 18x24 SLR) or Minolta SLRs. These are mainly of interest as collectibles. The Nickelodeon Photoblaster was a quarter-frame camera.