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 projector An overhead projector (often abbreviated to OHP), like a film or slide projector, uses light to project an enlarged image on a screen, allowing the view of a small document or picture to be shared with a large audience. In the overhead projec ...

s. 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 overhead projector. 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. Episkop BW 1

History

Swiss mathematician, physicist, astronomer, logician and engineer

Leonhard Euler Leonhard Euler ( , ; 15 April 170718 September 1783) was a Swiss mathematician, physicist, astronomer, geographer, logician and engineer who founded the studies of graph theory and topology and made pioneering and influential discoveries in ma ...

demonstrated an opaque projector around 1756. It could project a clear image of opaque images and (small) objects. French scientist

Jacques Charles Jacques Alexandre César Charles (November 12, 1746 – April 7, 1823) was a French inventor, scientist, mathematician, and balloonist. Charles wrote almost nothing about mathematics, and most of what has been credited to him was due to mistaking ...

is thought to have invented the similar "megascope" in 1780. He used it for his lectures. Around 1872 Henry Morton used an opaque projector in demonstrations for huge audiences, for example in the Philadelphia Opera House which could seat 3500 people. His machine did not use a condenser or reflector, but used an

oxyhydrogen Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases. This gaseous mixture is used for torches to process refractory materials and was the first gaseous mixture used for welding. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough ...

lamp close to the object in order to project huge clear images. The light source in early opaque projectors was often limelight.

Incandescent light bulb An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxid ...

s and

halogen lamp A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small ...

s 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 first by the

and later the

document camera Document cameras, also known as visual presenters, visualizers, digital overheads, or docucams, are real-time image capture devices for displaying an object to a large audience. Like an opaque projector, a document camera is able to magnify and p ...

, a lighted table with a fixed

video camera A video camera is an optical instrument that captures videos (as opposed to a movie camera, which records images on film). Video cameras were initially developed for the television industry but have since become widely used for a variety of oth ...

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. Opaque projectors are still in use for tracing, called tracing projectors. A flat or solid original is projected on a larger sheet of paper onto a wall or easel, where the artist or craftsperson can trace the outline reliably.

Types

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." Two main classes of opaque projectors thus existed: # the episcope, which solely projected images of opaque objects # the epidiascope, which was capable of projecting images of both opaque and transparent images

References

External links

Episcopes and epidiascopes
photographs of a collection.

Patent #803.385 for one of the earliest epidiascopes
{{DEFAULTSORT:Opaque Projector Projectors Display devices

History

Types

See also

References

External links