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PITCH One of the characteristics of perforations is their "pitch". This is the measurement of the distance between the top of two perforations in sequence. For 35 Mm Film and 16 Mm Film , there are two different pitches - short pitch (camera negative film) and long pitch (print stock, optical printers, bi-pack). For 35 mm these are 0.1866" and 0.187"; for 16 mm they are 0.2994" and 0.3". SHAPES BH/N Additionally, in 35 mm and 65/70 mm there are several different shapes for these perforations. BH (Bell and Howell) or '''N''' perforations are used in camera negative film and have straight top and bottom with outward curving sides and have been in use since the very beginning of the 20th century. They measure 0.073" in height and 0.11" from corner to middle of the opposite side. The corners used to be sharp, but were slightly rounded in the 1990s to give them greater strength. KS/P KS ( Kodak Standard) or '''P''' perforations were introduced in the 1920s to improve steadiness, registration, durability, and longevity and thus are used for intermediate and release prints as well as camera negatives which require it, such as high-speed filming, Bluescreen , Front Projection , Rear Projection , or Matte work. KS perfs are rectangular with rounded corners, and measure 0.078" high by 0.11" wide. Others Rarer perforations include DH (Dubray Howell), which goes back to 1931 and was a suggested replacement for both BH and KS perfs. It is also a rectangle with rounded corners and measures 0.073" high by 0.11" wide. It is still used for certain intermediate print stocks. '''CS''' (Cinemascope) perforations were briefly used for earlier Anamorphic Widescreen release prints and were narrower (0.078" high by 0.073" wide) than KS perfs so as to allow more room on the prints for extra magnetic soundtracks. Because all Cinemascope films were made by 20th Century Fox , they were also known as "Foxholes". 16 MM All 16 mm perforations are rectangles with rounded corners and are 0.05" high by 0.078" wide. The tolerance for these perforation dimensions was reduced to 0.01 mm in 1989, which allowed 16 mm camera manufacturers to slightly enlarge their registration pins and thus improve image registration and steadiness tolerances to less than 1/750th of the image height of the 16 mm frame. 8 MM Standard 8 Mm Film uses 16 mm film that is perforated twice as frequently (half the pitch of normal 16 mm) and then split down the middle after development. Super 8 uses slightly smaller perfs on film which is already 8 mm wide. Super 8 pitch is 0.1667" and perfs are 0.045" high by 0.036" wide. PLACEMENT All of the systems described above place the perforations down either one side (Standard and Super 8, Super 16) or both sides (35 mm and 65/70 mm). Standard 16 mm can be either (single or double perf); some older cameras require double perf, but most can handle either. Because most cameras can handle both and increased popularity of Super 16, most 16 mm stock manufactured today is single perf unless requested otherwise. Some obsolete formats such as 9.5 Mm Film and some variants of 17.5 Mm Film used a single perforation in the middle of the frame line between each image. This is considered more of a liability however, since any sprocket or claw error will likely damage the center of the frame itself rather than the outer edges. SEE ALSO |
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