A slide projector is an opto-mechanical device to view photographic

Photography

Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

 slides. Slide projectors were common in the 1950s to the 1970s as a form of entertainment; family members and friends would gather to view slide shows. In-home photographic slides and slide projectors have largely been replaced by low cost paper prints, digital cameras, DVD

DVD

A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

 media, video display monitors and video projector

Video projector

A video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other...

s.

A projector has four main elements:

• electric incandescent light bulb
  Incandescent light bulb
  The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...
  
   or other light source (usually fan-cooled)
• reflector and "condensing" lens to direct the light to the slide,
• holder for the slide and
• focusing lens
  Lens (optics)
  A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
  
  .

A flat piece of heat-absorbing glass is often placed in the light path between the condensing lens and the slide, to avoid damaging the latter. This glass transmits visible wavelengths but absorbs infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

. Light passes through the transparent slide and lens, and the resulting image is enlarged and projected onto a perpendicular flat screen

Projection screen

A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed, as in a movie theater; painted on the wall; or semi-permanent or mobile, as in a conference room...

 so the audience can view its reflection. Alternatively, the image may be projected onto a translucent "rear projection" screen, often used for continuous automatic display for close viewing. This form of projection also avoids the audience interrupting the light stream by casting their shadow on the projection or by bumping into the projector.

It is also increasingly difficult in some countries to locate photo processors who will process slide film. . Several manufacturers have stopped production of slide projectors.

Types of projector

• Carousel slide projector
  Carousel slide projector
  A carousel slide projector is a common form of slide projector, used to project slide photographs and to create slideshows. The first carousel slide projector was invented by Louis Misuraca, who immigrated to the United States from Naples, Italy when he was a child. Louis was paid a one-time fee...
  
  s
• Straight-tray slide projectors
• Dual slide projectors
• Overhead projector
  Overhead projector
  An overhead projector is a variant of slide projector that is used to display images to an audience.-Mechanism:An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light...
  
  s
• Single slide projectors (manual form)
• Viewer slide projectors
• Slide Cube projector
  Slide Cube projector
  A slide cube projector is a type of slide projector that was created by Bell & Howell and was sold up through the 1980s. The system gets its name from the plastic cubes that slides are stored in...
  
  s
• Stereo slide projectors (projects two slides simultaneously with different polarizations; slides appear as three-dimensional with polarizing glasses)
• Large Format Slide Projector
  Large Format Slide Projector
  A large-format slide projector is a kind of slide projector which has a very powerful light source...
  
  for uses on stages, for events or for architectural and advertising issues of high light output needs.