Editing 35 mm movie film (section)

==Perforations==
{{Main|Film perforations}}
[[File:35mm Film Sprockets.svg|right|thumb|35&nbsp;mm film perforation hole types.]]

===BH perforations=== 
Film perforations were originally round holes cut into the side of the film, but as these perforations were subject to wear and deformation, the shape was changed to what is now called the [[Böwe Bell & Howell|Bell & Howell]] (BH) perforation, which has straight top and bottom edges and outward curving sides. The BH perforation's dimensions are {{convert|0.110|in|mm}} from the middle of the side curve to opposite top corner by {{convert|0.073|in|mm}} in height.<ref name="case">{{cite book |last= Case |first=Dominic |title=Motion Picture Film Processing |location=Boston |publisher=Focal Press |year=1985 |isbn = 9780240512433}}</ref> The BH1866 perforation, or BH perforation with a [[Film perforations#Pitch|pitch]] of {{convert |0.1866|in|mm}}, is the modern standard for negative and internegative films.<ref name="Kodak motion film specs">{{cite web|url=http://motion.kodak.com/motion/uploadedFiles/US_plugins_acrobat_en_motion_newsletters_filmEss_11_Film_Specs.pdf#page=3 |archive-url=https://web.archive.org/web/20110107142747/http://motion.kodak.com/motion/uploadedFiles/US_plugins_acrobat_en_motion_newsletters_filmEss_11_Film_Specs.pdf |archive-date=2011-01-07 |url-status=live |title=Perforation Sizes and Shapes |publisher=[[Kodak]] |work=Motion Newsletters |date=October 30, 2007 |access-date=March 14, 2012 |page=95}}</ref>

===KS perforations===
Because BH has sharp corners, the repeated use of the film through intermittent movement projectors creates strain that can easily tear the perforations. Furthermore, they tended to shrink as the print slowly decayed. Therefore, larger perforations with a rectangular base and rounded corners were introduced by [[Kodak]] in 1924 to improve steadiness, registration, durability, and longevity. Known as "Kodak Standard" (KS), they are {{convert|0.0780|in|mm}} high by {{convert|0.1100|in|mm}} wide.<ref name="smpte139">{{cite book|title=ST 139:2003 - SMPTE Standard - For Motion-Picture Film (35-mm) — Perforated KS|date=12 November 2003|publisher=[[SMPTE]]|isbn=978-1-61482-313-1|doi=10.5594/SMPTE.ST139.2003}}</ref> Their durability makes KS perfs the ideal choice for some (but not all) intermediate and all release prints, and [[original camera negative]]s which require special use, such as high-speed filming, but not for [[Chroma key|bluescreen]], [[front projection]], [[rear projection]], or [[Matte (filmmaking)|matte]] work as these specific applications demand the more accurate registration which is only possible with BH or DH perforations. The increased height also means that the image registration was considerably less accurate than BH perfs, which remains the standard for negatives.<ref name="JSMPE May 1930">{{cite journal |author=Society of Motion Picture Engineers |date=May 1930 |title=Standards Adopted by the Society of Motion Picture Engineers |url=https://archive.org/stream/journalofsociety14socirich#page/552/mode/2up |journal=Journal of the Society of Motion Picture Engineers |volume=XIV |issue=5 |pages=545–566}}</ref><ref name="screensound">{{cite web |work=ScreenSound Australia |url=http://www.nfsa.afc.gov.au/preservation/audiovisual_terms/audiovisual_item.php?term=Perforations |title=Technical Glossary of Common Audiovisual Terms: Perforations |access-date=August 11, 2006 |archive-url=https://web.archive.org/web/20071031093815/http://www.nfsa.afc.gov.au/preservation/audiovisual_terms/audiovisual_item.php?term=Perforations |archive-date=October 31, 2007}}</ref> The KS1870 perforation, or KS perforation with a [[Film perforations#Pitch|pitch]] of {{convert|0.1870|in|mm}}, is the modern standard for release prints.<ref name="Kodak motion film specs" />

These two perforations have remained by far the most commonly used ones. BH perforations are also known as ''N'' (negative) and KS as ''P'' (positive). The Bell & Howell perf remains the standard for camera negative films because of its perforation dimensions in comparison to most printers, thus it can keep a steady image compared to other perforations.<ref name="Kodak motion film specs" /><ref name="gray">{{cite web |url=http://www.jkor.com/peter/perfs.html |title=Perforations/Sprocket Holes: Peter Gray - Director of Photography |year=1997 |access-date=March 14, 2012 |last=Gray |first=Peter |archive-url=https://web.archive.org/web/20080412041026/http://www.jkor.com/peter/perfs.html |archive-date=April 12, 2008}}</ref>

===DH perforations===
The Dubray–Howell (DH) perforation was first proposed in 1932<ref name="JSMPE April 1932">{{cite journal |url=https://archive.org/stream/journalofsociety18socirich#page/n513/mode/2up |title=Change in 355 Mm. Film Perforations |last=Howell |first=A.S. |journal=Journal of the Society of Motion Picture Engineers |date=April 1932 |volume=XVIII |issue=4 |oclc=1951231}}</ref><ref name="JSMPE Sept 1931">{{cite journal |url=https://archive.org/stream/journalofsociety17socirich#page/432/mode/2up |title=Committee Activities, Report of the Standards and Nomenclature Committee, Wide Film |journal=Journal of the Society of Motion Picture Engineers |date=September 1931 |volume=XVII |issue=3 |pages=431–436 |oclc=1951231 |publisher=The Society |location=New York, NY}}</ref> to replace the two perfs with a single hybrid. The proposed standard was, like KS, rectangular with rounded corners and a width of {{convert|0.1100|in|mm}}, and, like BH, was {{convert|0.073|in|mm}} tall.<ref name="achart" /><ref name="Kodak FAQ Sound Negative">{{cite web |url=http://motion.kodak.com/motion/Support/Technical_Information/Processing_Information/perforations.htm |title=Why Do Sound Negative Films Use Kodak Standard Perforations? |publisher=Kodak |work=Technical Information |access-date=March 14, 2012 |archive-url=https://web.archive.org/web/20120303172050/http://motion.kodak.com/motion/Support/Technical_Information/Processing_Information/perforations.htm |url-status=dead |archive-date=March 3, 2012}}</ref> This gave it longer projection life but also improved registration. One of its primary applications was usage in [[Technicolor]]'s dye imbibition printing (dye transfer).<ref name="gray" /> The DH perf never had broad uptake, and Kodak's introduction of monopack Eastmancolor film in the 1950s reduced the demand for dye transfer,<ref name="screensound" /> although the DH perforation persists in special application intermediate films.<ref name="dh">{{cite web |website=Eastman Kodak |url=http://www.kodak.com/US/en/motion/products/intermediate/tech5242.jhtml?id=0.1.4.6.4.4.4&lc=en |title=Kodak Vision Color Intermediate Film - Technical Data |access-date=August 11, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060905085939/http://www.kodak.com/US/en/motion/products/intermediate/tech5242.jhtml?id=0.1.4.6.4.4.4&lc=en |archive-date=September 5, 2006 }}</ref>

===CS perforations===
In 1953, the introduction of [[CinemaScope]] by [[20th Century Fox#Twentieth Century/Fox merger|Fox Studios]] required the creation of a different shape of perforation which was nearly square and smaller to provide space for four magnetic sound stripes for stereophonic and surround sound.<ref name="hone" /> These perforations are commonly referred to as CinemaScope (CS) or "Fox hole" perfs. Their dimensions are {{convert|0.0780|in|mm}} in width by {{convert|0.0730|in|mm}} in height.<ref name="smpte102">{{cite book |title=ST 102:2002 - SMPTE Standard - For Motion-Picture Film (35-mm) — Perforated CS-1870 |date=26 July 2002 |doi=10.5594/SMPTE.ST102.2002|publisher=[[SMPTE]] |isbn=978-1-61482-304-9}}</ref> Due to the size difference, CS perfed film cannot be run through a projector with standard KS sprocket teeth, but KS prints ''can'' be run on sprockets with CS teeth. Shrunken film with KS prints that would normally be damaged in a projector with KS sprockets may sometimes be run far more gently through a projector with CS sprockets because of the smaller size of the teeth. Magnetic striped 35&nbsp;mm film became obsolete in the 1980s after the advent of [[Dolby Stereo]], as a result film with CS perfs is no longer manufactured.

During continuous contact printing, the raw stock and the negative are placed next to one another around the sprocket wheel of the printer. The negative, which is the closer of the two to the sprocket wheel (thus creating a slightly shorter path), must have a marginally shorter pitch between perforations (0.1866&nbsp;in pitch); the raw stock has a long pitch (0.1870&nbsp;in). While cellulose nitrate and cellulose diacetate stocks used to shrink during processing slightly enough to have this difference naturally occur, modern safety stocks do not shrink at the same rate, and therefore negative (and some intermediate) stocks are perforated at a pitch of 0.2% shorter than print stock.<ref name="case" />