This is a waist level viewfinder for the Pentax 6x7 or Pentax 67 Camera body.
The Pentax 6x7 (known as Pentax 67 after 1990) is an SLR medium format system film camera for 120 and 220 film, which produces images on the film that are nominally 6 cm by 7 cm in size (56mm by 70mm in the film gate), made by Pentax. It originally debuted in 1965 as a prototype dubbed the Pentax 220. Since then and with improvements, it was released in 1969 as the Asahi Pentas 6×7, as well as the Honeywell Pentax 6×7 for the North American import market. In 1990, it received a number of minor engineering updates and cosmetic changes and was renamed as the Pentax 67.
The camera resembles a traditional 35 mm SLR camera with an interchangeable viewfinder and lens, but is considerably bigger and heavier, weighing 2.3 kilograms (5.1 lb) with the plain prism and standard (105 mm f/2.4) lens.
The Pentax 6×7 has a dual bayonet lens mount, and a wide range of interchangeable Takumar and later SMC Pentax 67-designated lenses exist. More than forty years after the original camera introduction a wide selection of lenses is still available, together with the latest Pentax 67II variant.
The following models have been issued:
Asahi Pentax 6×7 – the original model, launched in 1969 (first generation)
Asahi Pentax 6×7 (MLU) – with a mirror lock-up mechanism, launched in 1976 (second generation)
See the two videos below of this camera in action:
In the video below, Dan Rubin shoots with the Pentax 67, amongst other cameras.