The opaque projector, episcope or epidiascope 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".
Suitable objects included book pages, drawings, mineral specimens, leaves, etc. In the early and mid 20th century, opaque projectors were produced as low cost toy projectors for children, were also marketed as an artist's enlargement tool to allow images to be transferred to prepared canvas, or for lectures and discourses.
See also
- Projector for a directory of projector types.
External links
- Episcopes and epidiascopes, photographs of a collection.
- Historic Ross Epidiascope
- Brief description of the modern Braun Paxiscope XL Epidiascope.
- Digital epidiascope from Samsung.
