Slide projector in the context of "Magic lantern"

A planetarium (pl.: planetariums or planetaria) is a theatre built primarily for presenting educational and entertaining shows about astronomy and the night sky, or for training in celestial navigation.

A dominant feature of most planetariums is the large dome-shaped projection screen onto which scenes of stars, planets, and other celestial objects can be made to appear and move realistically to simulate their motion. The projection can be created in various ways, such as a star ball, slide projector, video, fulldome projector systems, and lasers. Typical systems can be set to simulate the sky at any point in time, past or present, and often to depict the night sky as it would appear from any point of latitude on Earth.

In photography, reversal film, or slide film, is a type of photographic film that produces a positive image on a transparent base. Instead of negatives and prints, reversal film is processed to produce transparencies, or diapositives (abbreviated as "diafilm" or "dia" in some languages like German, Romanian or Hungarian). Reversal film is produced in various sizes, from 35 mm to roll film to 8×10 inch sheet film.

A slide is a specially mounted individual transparency intended for projection onto a screen using a slide projector. This allows the photograph to be viewed by a large audience at once. The most common form is the 35 mm slide, with the image framed in a 2×2 inch cardboard or plastic mount. Some specialized labs produce photographic slides from digital camera images in formats such as JPEG, from computer-generated presentation graphics, and from a wide variety of physical source material such as fingerprints, microscopic sections, paper documents, astronomical images, etc.

In optical engineering, an objective is an optical element that gathers light from an object being observed and focuses the light rays from it to produce a real image of the object. Objectives can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.

In photography and optics, vignetting (/vɪnˈjɛtɪŋ/ vin-YET-ing) is a reduction of an image's brightness or saturation toward the periphery compared to the image center. The word vignette, from the same root as vine, originally referred to a decorative border in a book. Later, the word came to be used for a photographic portrait that is clear at the center and fades off toward the edges. A similar effect is visible in photographs of projected images or videos off a projection screen, resulting in a so-called "hotspot" effect.

Vignetting is often an unintended and undesired effect caused by camera settings or lens limitations. However, it is sometimes deliberately introduced for creative effect, such as to draw attention to the center of the frame. A photographer may deliberately choose a lens that is known to produce vignetting to obtain the effect, or it may be introduced with the use of special filters or post-processing procedures.

A video projector is an image projector that receives a video signal and projects the corresponding image onto a projection screen using a lens system. Video projectors use a very bright ultra-high-performance lamp (a special mercury arc lamp), Xenon arc lamp, metal halide lamp, LED or solid state blue, RB, RGB or fiber-optic lasers to provide the illumination required to project the image. Most modern projectors can correct any curves, blurriness and other inconsistencies through manual settings.

Video projectors are used for many applications such as conference room presentations, classroom training, home cinema, movie theaters, and concerts, having mostly replaced overhead, slide and conventional film projectors. In schools and other educational settings, they are sometimes connected to an interactive whiteboard. In the late 20th century, they became commonplace in home cinema. Although large LCD television screens became quite popular, video projectors are still common among many home theater enthusiasts. In some applications, video projectors have been replaced with large monitors or LED screens, or their replacement has been explored.

An overhead projector (often abbreviated to OHP), like a film or slide projector, uses light to project an enlarged image on a screen, allowing the view of a small document or picture to be shared with a large audience.

In the overhead projector, the source of the image is a page-sized sheet of transparent plastic film (also known as "viewfoils", "foils", "acetate" or "transparencies") with the image to be projected either printed or hand-written/drawn. These transparent sheets are placed on the glass platen of the projector, which has a light source below it and a projecting mirror and lens assembly above it (hence, "overhead"). They were widely used in education and business before the advent of video projectors.

A slide show, or slideshow, is a presentation of a series of still images (slides) on a projection screen or electronic display device, typically in a prearranged sequence. The changes may be automatic and at regular intervals or they may be manually controlled by a presenter or the viewer. Slide shows originally consisted of a series of individual photographic slides projected onto a screen with a slide projector, as opposed to the video or computer-based visual equivalent, in which the slides are not individual physical objects.

A slide show may be a presentation of images purely for their own visual interest or artistic value, sometimes unaccompanied by description or text, or it may be used to clarify or reinforce information, ideas, comments, solutions or suggestions which are presented verbally. Slide shows are sometimes still conducted by a presenter using an apparatus such as a carousel slide projector or an overhead projector, but now the use of an electronic video display device and a computer running presentation software is typical.