Editing 35 mm movie film (section)

===Academy format===
{{Main|Academy ratio}}
[[File:35 mm film (Academy Ratio).svg|thumb|right|upright=1.5|Academy Ratio (4-perf) format diagram]]
In the conventional motion picture format, frames are four perforations tall, with an [[aspect ratio (image)|aspect ratio]] of 1.375:1, {{convert|22|by|16|mm|in|3|abbr=on}}. This is a derivation of the aspect ratio and frame size designated by Thomas Edison ({{convert|24.89|by|18.67|mm|disp=or}}) at the dawn of motion pictures, which was an aspect ratio of 1.33:1.<ref>{{cite book|last=Belton|first=John |title=Widescreen Cinema |url=https://books.google.com/books?id=PKUfAQAAIAAJ |year=1992 |publisher=Harvard University Press |location=Cambridge, Mass. |isbn=978-0-674-95261-4 |pages=17–18}}</ref> The first sound features were released in 1926–27, and while [[Warner Bros.]] was using synchronized phonograph discs ([[sound-on-disc]]), [[Fox Film Corporation|Fox]] placed the soundtrack in an optical record directly on the film ([[sound-on-film]]) on a strip between the sprocket holes and the image frame.<ref name="early sound">{{cite book |last=Dibbets |first=Karel |chapter=The Introduction of Sound |title=The Oxford History of World Cinema |publisher=Oxford University Press |location=Oxford |year=1996}}</ref> "Sound-on-film" was soon adopted by the other Hollywood studios, resulting in an almost square image ratio of 0.860&nbsp;in by 0.820&nbsp;in.<ref name="SMPE1930">{{cite journal |last=Cowan |first=Lester |title=Camera and Projector Apertures in Relation to Sound on Film Pictures |journal= Journal of the Society of Motion Picture Engineers|volume=14 |date=January 1930 |pages=108–121|doi=10.5594/J14828 }}</ref>

By 1929, most movie studios had revamped this format using their own house aperture plate size to try to recreate the older screen ratio of 1.33:1. Furthermore, every theater chain had their own house aperture plate size in which the picture was projected. These sizes often did not match up even between theaters and studios owned by the same company, and therefore, uneven projection practices occurred.<ref name="SMPE1930"/>

In November 1929, the [[Society of Motion Picture Engineers]] set a standard aperture ratio of 0.800&nbsp;in by 0.600&nbsp;in. Known as the "1930 standard", studios which followed the suggested practice of marking their camera viewfinders for this ratio were: Paramount-Famous-Lasky, Metro-Goldwyn Mayer, United Artists, Pathe, Universal, RKO, Tiffany-Stahl, Mack Sennett, Darmour, and Educational. The Fox Studio markings were the same width but allowed .04&nbsp;in more height.<ref>{{cite journal |title=Studios Seek to Aid Towards Better Projection Goal |journal=Movie Age |date=November 9, 1929 |page=18}}</ref>

In 1932, in refining this ratio, the [[Academy of Motion Picture Arts and Sciences]] expanded upon this 1930 standard. The camera aperture became {{convert|22|by|16|mm|in|abbr=on}}, and the projected image would use an aperture plate size of {{convert|0.825|by|0.600|in|mm|abbr=on}}, yielding an aspect ratio of 1.375:1. This became known as the "[[Academy ratio|Academy]]" ratio.<ref name="1.375">{{cite book|editor-last=Hummel|editor-first=Rob |title=American Cinematographer Manual |edition=8th |pages=18–22 |publisher=ASC Press |location=Hollywood |year=2001}}</ref> Since the 1950s the aspect ratio of some theatrically released motion picture films has been 1.85:1 (1.66:1 in Europe) or 2.35:1 (2.40:1 after 1970). The image area for "TV transmission" is slightly smaller than the full "Academy" ratio at {{convert|21|by|16|mm|in|abbr=on}}, an aspect ratio of 1.33:1. Hence when the "Academy" ratio is referred to as having an aspect ratio of 1.33:1, it is done so mistakenly.<ref name="1.375" />