/ˈɛp.ɪ.skoʊp/

Episcope

noun · optics

Part of the drawing glossary behind the 82 composition overlays every visual artist should know and use.

What it is

An episcope is the optical assembly that makes reflective projection possible. A bright lamp illuminates a solid, non-transparent original; a mirror and lens then collect the light bouncing off its surface and cast an enlarged image onto a screen or wall. It is, in essence, the working core of the opaque projector — the term names the optical principle rather than the boxed consumer product built around it.

The distinction that matters is what the device can accept as a source. An episcope handles opaque originals only — a photo, a page, a drawing. An epidiascope combines two light paths so it can project either an opaque original (by reflection) or a transparent one such as a slide (by transmission). The transmissive-only cousin, which projects only transparencies, is the diascope. For an artist tracing a small reference up to full size, the episcope's reflective path is the one that removes the need to first make a slide.

Etymology

"Episcope" is built from the Greek epi-, "upon," and skopein, "to look" — literally an instrument for looking upon a surface, fitting for a device that reads light off the face of an opaque object. The companion term "epidiascope" adds dia-, "through," to signal the second, transmissive light path that lets it project transparent originals as well. Both words entered technical English through late-19th and early-20th-century optics, the era when reflective and combined projectors became standard classroom and studio equipment.

Examples in use

A lecturer of that era slotted a book page under the episcope to throw a diagram onto the wall for the whole room. An artist used the same reflective path to enlarge a small study before tracing it. Museum and teaching catalogues distinguished an "episcope" from an "epidiascope" precisely by whether the machine could also take slides. Today the same enlarge-and-trace task is handled without optics at all by the AR tracing app, which registers the reference over the real surface on a phone screen, while the light box covers the same-size, thin-paper case the episcope never addressed.