This instrument projects the image of a solid (or opaque) object. Bright light is concentrated on the object (eg a page of a book) and the image is reflected by a mirror through a large lens on to a screen.
The episcope enable object such a books, maps, pictures and three-dimensional models to show up as large clear images on a screen. But it is a fairly cumbersome piece of equipment and not really post-able. Also it produces a great concentration of heat which may destroy-flimsy material. Episcopes projects of p to 10in square, producing sharp colour image measuring 13ft x 13ft. Because only the reflected light is used to illuminate the screen the system is rather inefficient and a complete blackout is necessary.
The projector can project a picture from a magazine or a map on to a blackboard and the outline of the figure can be drawn in with white chalk.
The Epidiasope
The epidiascope combines the function of an episcope and a diascope; the latter by means of a lens system concentrates or condenses light which is then passed through a slide transparency and focused on to a screen. An epidiascope is a machine which projects lantern slides, ie 3/14in x 3/14in slides. By the addition of a supplementary optical system the episcope becomes an epidiascope. Other attachments can be added to the epidiascope for projecting filmstrips and 2in x 2in slides. But these may cost as much as a separate which can perform the same function with greater efficiency.
In America slides are 3/14in x 4/12in and on the Continent 9cn x12cm. like the episcope the epidiascope is a rather bulky piece of equipment.