Opaque projector

Opaque projector
An episcope which was used in a University of Cambridge lecture hall in the late 1800s

The opaque projector, epidioscope, epidiascope or episcope is a device which displays opaque materials by shining a bright lamp onto the object from above. A system of mirrors, prisms and/or imaging lenses is used to focus an image of the material onto a viewing screen. Because they must project the reflected light, opaque projectors require brighter bulbs and larger lenses than overhead projectors. Care must be taken that the materials are not damaged by the heat generated by the light source. Opaque projectors are not as common as the modern "overhead".

Opaque projectors are typically used to project images of book pages, drawings, mineral specimens, leaves, etc. They have been produced and marketed as artists’ enlargement tools to allow images to be transferred to surfaces such as prepared canvas, or for lectures and discourses.

Small Episcope for home use



The opaque projector is a predecessor to the overhead projector. The light source in early opaque projectors was often limelight. Incandescent light bulbs and halogen lamps are most commonly used today. In the early and middle parts of the 20th century, low-cost opaque projectors were produced and marketed as toys for children.

In educational settings, the specific role of the opaque projector has been superseded by the document camera, a lighted table with a fixed video camera above it. The image from the camera is displayed using a separate projector. The document camera is also called a desktop presenter unit or opaque projector.


At the beginning of the 20th century, projection was split into two classes: " If the light traverses the object, the projection is said to be diascopic, if by reflected light, episcopic.".[1]

Two main classes of opaque projectors thus existed:

  1. the episcope, which solely projected images of opaque objects
  2. the epidiascope, which was capable of projecting images of both opaque and transparent images

See also

  • Projector (disambiguation) for a directory of projector types.


  1. ^ Encyclopaedia Britannica. [1]: University of Cambridge. 1911. 

External links

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Look at other dictionaries:

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  • opaque projector — opaque projecting. a machine for projecting opaque objects, as books, on a screen, by means of reflected light. [1950 55] * * * …   Universalium

  • opaque projector — opaque′ projec′tor n. pht a machine for projecting opaque objects, as books, on a screen, by means of reflected light • Etymology: 1950–55 …   From formal English to slang

  • opaque projector — noun Date: 1951 a projector using reflected light for projecting an image of an opaque object or matter on an opaque support (as a photograph) …   New Collegiate Dictionary

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  • Projector — may refer to:* Video projector, a device that projects a video signal from computer, home theater system etc. * Movie projector, a device that projects moving pictures from a filmstrip * Slide projector, a device that projects a still image with… …   Wikipedia

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  • projector — n. 1) to operate, work a projector 2) a cine projector (BE), film, motion picture (AE); opaque; overhead; slide projector * * * [prə dʒektə] film opaque overhead slide projector work a projector motion picture (AE) to operate a c …   Combinatory dictionary

  • projector — /preuh jek teuhr/, n. 1. an apparatus for throwing an image on a screen, as a motion picture projector or magic lantern. 2. a device for projecting a beam of light. 3. a person who forms projects or plans; schemer. [1590 1600; PROJECT + OR2] * *… …   Universalium

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