A slide projector is an opto-mechanical device to view photographic slides. The slide projector comprises means in which to project an image perpendicularly from a slide onto a projection surface. A slide projector has four main elements: a fan-cooled electric light bulb or other light source, a reflector and "condensing" lens to direct the light to the slide, a holder for the slide and a focusing lens. In use, the projected image of the slide lies in a substantially planar surface. 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. The slide is located in a rotating carousel which can be automatically, or manually, rotated, thus providing accurate simulation of the orientation of stars and other celestial bodies at a specific date and time. Types of slide projectors include carousel slide projectors (includes tray-style projectors), dual slide projectors, single slide projectors (manual form), viewer slide projectors, slide cube projectors, stereo slide projectors (projects two slides simultaneously with different polarizations; slides appear as three-dimensional with polarizing glasses).
