Editing Depth of field (section)

=== Effect of circle of confusion===
Precise focus is only possible at an exact distance from a lens;{{Efn|Strictly, at an exact distance from a plane.}} at that distance, a point object will produce a small spot image. Otherwise, a point object will produce a larger or blur spot image that is typically and approximately a circle. When this circular spot is sufficiently small, it is visually indistinguishable from a point, and appears to be in focus. The diameter of the largest circle that is indistinguishable from a point is known as the [[acceptable circle of confusion]], or informally, simply as the circle of confusion.

The acceptable circle of confusion depends on how the final image will be used. The circle of confusion as 0.25&nbsp;mm for an image viewed from 25&nbsp;cm away is generally accepted.{{sfn|Savazzi|2011|p=109}}

For [[35mm movie film|35{{nbsp}}mm]] motion pictures, the image area on the film is roughly 22&nbsp;mm by 16&nbsp;mm. The limit of tolerable error was traditionally set at {{convert|0.05|mm|in|abbr=on}} diameter, while for [[16 mm film|16&nbsp;mm film]], where the size is about half as large, the tolerance is stricter, {{convert|0.025|mm|in|abbr=on}}.<ref>{{Cite book|title=Film and Its Techniques|date=1966|publisher=University of California Press|page=56|url=https://books.google.com/books?id=Ocfs3ZsLresC&q=35+mm+motion+picture+film+circle+of+confusion&pg=PA56|access-date=24 February 2016}}</ref> More modern practice for 35&nbsp;mm productions set the circle of confusion limit at {{convert|0.025|mm|in|abbr=on}}.<ref>{{Cite book|author=Thomas Ohanian and Natalie Phillips|title=Digital Filmmaking: The Changing Art and Craft of Making Motion Pictures|date=2013|publisher=CRC Press|isbn=9781136053542|page=96|url=https://books.google.com/books?id=usMqBgAAQBAJ&q=35+mm+motion+picture+film+circle+of+confusion&pg=PA96|access-date=24 February 2016}}</ref>