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.