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| FAQ: Opaque projector |
Opaque projector?
The opaque projector, epidioscope, epidiascope or episcope is a predecessor to the overhead projector. It displays opaque materials by shining a bright lamp, often limelight, 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. 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In educational settings, the specific role of the opaque projector has been superseded by the presenter, a lighted table with a fixed video camera above it. The image from the camera is displayed using a separate projector. The desktop presenter unit is sometimes called an opaque projector.
The above refers to the 'epi' part of the epidiascope. The epidiascope is a combined version of the episcope. The 'dia' part providing also the ability to project glass slides approx 100mm x100mm, using a slide carrier on the front of the box integral with the projector lenses.
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