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What is an Epidiascope?

Malcolm Tatum
Updated May 16, 2024
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The epidiascope is a type of opaque projector developed in the early years of the 20th century. Unlike the episcope or epidioscope, which have the ability to project opaque images only, epidiascopes can project images of both transparent and opaque images. This quality made the device especially useful in educational circles for most of the century.

The basic functionality of the epidiascope involved harnessing the power of light to create the images. In the earliest models of the epidiascope and other similar projectors, limelight was used as the medium. The light would be directed downward onto an object, creating the image. To focus the light and create a viable image, a series of lenses or mirrors would be used to direct the image onto a screen. While somewhat costly to produce at first, the epidiascope became more affordable as the device was refined. Along with commercial models, low powered versions were produced and marketed as toys for school age children.

By the middle of the 20th century, the typical epidiascope was produced using incandescent light as the source for creating the image. Desktop models of the device were in common use in schools and colleges across the globe. Within a few years, halogen lamps began to replace the incandescent bulbs, providing an even sharper projected image.

As the era of the personal computer dawned in the 1980’s, new technology began to replace the epidiascope. Utilizing projectors that would attach easily to desktop and laptop computers, it became possible to create images using software and project the results onto an overhead screen. The combination of a laptop and a projector made it possible for salespersons to take along presentations and other documents to meetings with new clients or show presentations at trade shows with much greater ease.

While not used as extensively as in times past, the epidiascope is still sometimes used in schools and other learning settings. Because the transparencies used with an epidiascope can be created using computer programs or by hand, the device has remained in service and is still offered for sale by a number of manufacturers.

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Malcolm Tatum
By Malcolm Tatum , Writer
Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing to become a full-time freelance writer. He has contributed articles to a variety of print and online publications, including EasyTechJunkie, and his work has also been featured in poetry collections, devotional anthologies, and newspapers. When not writing, Malcolm enjoys collecting vinyl records, following minor league baseball, and cycling.

Discussion Comments

By Rundocuri — On Feb 09, 2014

Your post brings back good memories Talentryto. Kids today wouldn't even know what slide viewers or film strip projectors are compared to today's devices.

By Talentryto — On Feb 08, 2014

This article reminds me of the 35mm slide viewers used to look at family vacation slides and the old film strip projectors use for educations films in grade school. It's amazing how far technology has come since those types of projectors were considered to be cutting edge.

Malcolm Tatum

Malcolm Tatum


Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing...
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