Editing Camera obscura (section)

==Technology==
[[File:Camera Obscura box18thCentury.jpg|thumb|A ''camera obscura'' box with mirror, with an upright projected image at the top]]

A ''camera obscura'' consists of a box, tent, or room with a small hole in one side or the top. Light from an external scene passes through the hole and strikes a surface inside, where the scene is reproduced, inverted (upside-down) and reversed (left to right), but with color and [[perspective (graphical)|perspective]] preserved.<ref name="mass">{{cite book |author1=Melvin Lawrence DeFleur |author1-link=Melvin Defleur |author2=Sandra Ball-Rokeach |author2-link=Sandra Ball-Rokeach |title=Theories of Mass Communication |date=1989 |publisher=Longman |isbn=9780801300073 |page=65 |edition=5 |url=https://books.google.com/books?id=Ywe4AAAAIAAJ |access-date=11 January 2021 |archive-date=10 November 2023 |archive-url=https://web.archive.org/web/20231110061238/https://books.google.com/books?id=Ywe4AAAAIAAJ |url-status=live }}</ref>

To produce a reasonably clear projected image, the aperture is typically smaller than 1/100 the distance to the screen.
As the pinhole is made smaller, the image gets sharper, but dimmer. With too small of a pinhole, sharpness is lost because of [[diffraction]]. Optimum sharpness is attained with an aperture diameter approximately equal to the [[geometric mean]] of the wavelength of light and the distance to the screen.<ref name="physics">{{cite book |author=Heinrich F. Beyer and Viateheslav P. Shevelko |title=Introduction to the Physics of Highly Charged Ions |date=2016 |publisher=CRC Press |isbn=9781420034097 |page=42 |url=https://books.google.com/books?id=5enLBQAAQBAJ&pg=PA42 |access-date=11 January 2021 |archive-date=10 November 2023 |archive-url=https://web.archive.org/web/20231110061238/https://books.google.com/books?id=5enLBQAAQBAJ&pg=PA42#v=onepage&q&f=false |url-status=live }}</ref>

In practice, ''camera obscuras'' use a [[Lens (optics)|lens]] rather than a pinhole because it allows a larger [[aperture]], giving a usable brightness while maintaining focus.<ref name="amateur work"/>

If the image is caught on a translucent screen, it can be viewed from the back so that it is no longer reversed (but still upside-down).  Using mirrors, it is possible to project a right-side-up image. The projection can also be displayed on a horizontal surface (e.g., a table). The 18th-century overhead version in tents used mirrors inside a kind of periscope on the top of the tent.<ref name="amateur work"/>

The box-type ''camera obscura'' often has an angled mirror projecting an upright image onto [[tracing paper]] placed on its glass top. Although the image is viewed from the back, it is reversed by the mirror.<ref>{{cite book |last1=Steadman |first1=Philip |title=Vermeer's Camera: Uncovering the Truth Behind the Masterpieces |date=2002 |publisher=Oxford University Press |isbn=9780192803023 |page=9 |url=https://books.google.com/books?id=9Xu6lJc2Nt8C |access-date=11 January 2021 |archive-date=10 November 2023 |archive-url=https://web.archive.org/web/20231110061238/https://books.google.com/books?id=9Xu6lJc2Nt8C |url-status=live }}</ref>