Polaroid (polarizer) Polaroid (polarizer) Polaroid is a type of synthetic plastic sheet which is used as a polarizer or polarizing filter. A trademark of the Polaroid Corporation, the term has since entered common use. The original material, patented in 1929 and further developed in 1932 by Edwin H. Land, consists of many microscopic crystals of iodoquinine sulphate (herapathite) embedded in a transparent nitrocellulose polymer film. The needle-like crystals are aligned during manufacture of the film by stretching or by applying electric or magnetic fields. With the crystals aligned, the sheet is dichroic: it tends to absorb light which is polarized parallel to
History of the single-lens reflex camera 220 film to produce 6 cm × 6 cm (2" × 2") negatives. They also produce other film backs which produce a 6 cm × 4.5 cm image; a back which uses 70mm roll film, a Polaroid Back for instant 'proofs' and even a 35mm film back. Pentax produces two medium-format SLR systems, the Pentax 645, which produces a 6 cm × 4.5 cm image; and the Pentax 67 series, which system evolved from the late 1960s introduced Pentax 6 × 7 camera. These Pentax 6 × 7 series cameras resembled huge 35mm SLR camera in look and function. In