Editing Transparency (projection)

{{Short description|Plastic sheet for an overhead projector}}
{{More citations needed|date=December 2009}}
[[Image:OHP-sch.JPG|thumb|right|300px|Overhead projector in operation, with a transparency being flashed]]
A '''transparency''', also known variously as a '''viewfoil''' or '''foil''' (from the French word "feuille" or sheet), or '''viewgraph''', is a thin sheet of [[transparency (optics)|transparent]] flexible material, typically [[polyester]] (historically [[cellulose acetate]]), onto which figures can be drawn. These are then placed on an [[overhead projector]] for display to an audience. Many companies and small organizations use a system of projectors and transparencies in meetings and other groupings of people, though this system is being largely replaced by [[video projector]]s and [[interactive whiteboard]]s.

== Printing ==
Transparencies can be printed using a variety of technologies.  In the 1960s and 70s the GAF OZALID "projecto-viewfoil" used a diazo process to make a clear sheet framed in cardboard and protected by a rice paper cover.<ref>{{cite book|last=OZALID Newsletter|title=Electronics Weekly Magazine, November|year=1963|publisher=Electronics Weekly|url=https://www.worldradiohistory.com/Archive-Electronics/60s/63/Electronics-1963-11-08.pdf|access-date=2024-02-25}}</ref> In the 1980's [[laser printer]]s or [[copier]]s could make foil sheets using standard xerographic processes. Specialist transparencies are available for use with laser printers that are better able to handle the high temperatures present in the fuser unit. For inkjet printers, coated transparencies are available that can absorb and hold the liquid ink—although care must be taken to avoid excessive exposure to moisture, which can cause the transparency to become cloudy; they must also be loaded correctly into the printer as they are only usually coated on one side.

== Uses ==
Uses for transparencies are as varied as the organizations that use them.

Certain classes, such as those associated with [[mathematics]] or [[history]] and [[geography]] use transparencies to illustrate a point or problem. Until the advent of [[LaTeX]], math classes in particular used rolls of acetate to illustrate sufficiently long problems and to display mathematical symbols missing from common computer keyboards.

Aerospace companies, like [[Boeing]] and [[Beechcraft]], used transparencies for years in management meetings in order to brief engineers and relevant personnel about new aircraft designs and changes to existing designs, as well as bring up illustrated problems.<ref>{{cite book|last=Serling|first=Robert J.|title=Legend and Legacy: The Story of Boeing and Its People|year=1992|publisher=St. Martin's Press|isbn=0-312-05890-X|pages=[https://archive.org/details/legendlegacystor00serl/page/449 449]|url-access=registration|url=https://archive.org/details/legendlegacystor00serl/page/449}}</ref>

Some churches and other religious organizations used them to show sermon outlines and illustrate certain topics such as [[Old Testament]] battles and [[Jewish]] artifacts during worship services, as well as outline business meetings.

== Spatial light modulators (SLMs) ==
{{Unreferenced section|date=June 2017}}

Many [[overhead projector]]s are used with a flat-panel [[Liquid-crystal display|LCD]] which, when used this way, is referred to as a [[spatial light modulator]] or SLM. Data projectors are often based on some form of SLM in a projection path. An LCD is a transmissive SLM, whereas other technologies such as Texas Instrument's [[Digital Light Processing|DLP]] are reflective SLMs. Not all projectors use SLMs (e.g., some use devices that produce their own light rather than function as transparencies).  An example of non-SLM system are [[organic light-emitting diode]]s (OLEDs).

== See also ==
* [[Presentation slide]]
* [[Projection panel]]
* [[Reversal film]]

==References==
{{Reflist}}

==External links==
* [https://www.semanticscholar.org/topic/Transparency-(projection)/82752 Transparency (projection)] – semanticscholar.org

{{Display technology}}
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[[Category:Display technology]]
[[Category:Office equipment]]
[[Category:Presentation]]