Slide projector
A mechanical device to view photographic slides, a slide projector has four main elements: a fan-cooled electric light bulb or other light source, reflector andor "condensing" lens to direct the light to the slide, a holder for the slide and a focusing lens. Light passes through the transparent slide and lens, and the resulting image is enlarged and projected onto a perpendicular flat screen so the audience can view its reflection. Alternativly the image may be projected onto a translucent "rear projection" screen.
Most slide projectors have a slotted carousel or cube-shaped tray attachment to conveniently store multiple (e.g. 20, 36, 80) 35mm slides. The operator sequentially fills the tray (upside down and backwards) with slides, and after mounting the tray to the projector, a reciprocating mechanism loads/unloads each slide between the light source and lens, producing a slide show.
The resolution and color brilliance of good quality 35mm slides far exceed that of modern in-home video.
Common in the 1950s and 1960s households as an alternate to television or movie entertainment, family members and friends would gather, darken the living room and show slides of recent holidays or vacations, an often boring affair that incited heckling, catcalls and sleep.
In-home photographic slides and slide projectors have largely been replaced by low cost paper prints, digital cameras, DVD media, video display monitors and projectors.