Slide projector

A 1960 slide projector

A slide projector is an optical device for projecting enlarged images of photographic slides onto a screen. Many projectors have mechanical arrangements to show a series of slides loaded into a special tray sequentially.

35 mm slide projectors, direct descendants of the larger-format magic lantern, first came into widespread use during the 1950s for slide shows as home entertainment, and for use by educational and other institutes. Reversal film created a small positive projectable image rather than the negatives used since the early days of photography; photography now produced 35mm directly viewable small colour slides, rather than large monochrome negatives. The slide images were too small for unaided viewing, and required enlargement by a projector or enlarging viewer.

Photographic film slides and projectors have been replaced by image files on digital storage media shown on a projection screen by using a video projector, or displayed on a large-screen video monitor.

History

• 
  Continuous-Slide Lantern, c. 1881
• 
  A Kodak Carousel model 4400 slide projector, first sold in the mid-1980s
• 
  Self-contained slide projector with rear-projection screen and carousel tray

A continuous-slide lantern was patented in 1881. It included a dissolving views apparatus.

Design

Optics

Slide projector light generation and collimation system: from left to right, mirror / reflector, bulb, condenser lens 1, green-tinted heat-absorbing glass, condenser lens 2; a centrifugal fan, used to cool the bulb, is visible at the top of the picture.

A projector has three main optical elements:

• high luminous flux electric incandescent light bulb or other light source, usually fan-cooled
• reflector and condenser lens system to direct the light through the slide
• focusing projection lens

Philips halogen lamp used in Carl Braun Camera-Werk Novamat M 330 slide projector

An incandescent lamp bulb is used to generate light, usually specially designed to have a small, bright filament to produce a sharp and bright image. For example, the Leitz Pradovit RC uses a special 24V 150W quartz lamp, with provision to center it, required for best performance. This projector had provision to reduce lamp power by 20% to double its life (50 hours at full brightness).

Light from the bulb is modified from a point source by reflection and passing through condenser lens(es) to generate a collimated beam, which is then directed through the slide. A flat piece of heat-absorbing glass is usually placed in the light path before the slide, to avoid damaging the latter. This glass transmits visible wavelengths but absorbs infrared.

This slide projector, sold under the Zeiss Ikon brand, uses a straight-through tray; a thin arm is used to put slides into the light path from a tray which is advanced horizontally. At the front of the projector, the protruding projection lens features rings to control focal length and focus.

After the collimated beam passes through the transparent slide, it is enlarged by a projection lens onto a flat projection screen so the audience can view the reflected image. For some slide projectors, the projection lens is removable and may be swapped with alternative lens(es) to change the brightness or focal length(s), which may affect potential size of the image or the distance from the screen required for a certain projected image size, respectively.

Alternatively, the image may be projected onto a translucent "rear projection" screen, often used for continuous automatic display for close viewing. For example, the Bell & Howell RingMaster, manufactured by EIKI, projected slides onto a flat screen approximately the size and shape of a small CRT TV; the RingMaster also could be used for front projection for larger audiences. This form of projection also avoids the potential of the audience interrupting the projected light beam by casting their shadows on the projection or by bumping into the projector.

Some slide projectors required users to manually place each slide that was being shown. Starting in the 1950s, manufacturers introduced slide projectors with mechanisms which handle slides preloaded into cartridges, moving individual slides into and out of the light path in sequence. One of the primary differentiators between slide projectors was the form factor of the cartridges used to hold and, in many cases, store slides. The early automated slide projectors offered slide trays with rectangular shapes. In the United States, Eastman Kodak introduced Carousel slide projectors in 1961, which used a rotary cartridge, and the format soon became ubiquitous there.

Types

Slide projectors proper:

• Straight-tray slide projectors have a straight magazine holding several slides.
• Carousel slide projectors have a circular magazine holding several slides.
• Stack-loader slide projectors
• Bell & Howell Slide Cube Projector had a cube-shaped magazine holding several slides.
• Dual slide projectors
• Single slide projectors project a single slide at a time, changed by the operator.
• Dissolve projectors
• Stereo slide projectors project two slides simultaneously with different polarizations, making slides appear as three-dimensional to viewers wearing polarizing glasses
• Medium-format slide projectors, for medium-format slides larger than 35mm.
• Specialised large-format slide projectors for large transparencies of 18 × 18 cm (7.1 × 7.1") or larger.

Related devices:

• Overhead projectors, for page-sized transparencies
• Slide viewer, for direct viewing of a magnified image of a slide

Manufacturers

List of known manufacturers of slide projectors:

• Agfa Gevaert, Germany (–1984) → Reflecta (1984–)
• Bauer, Germany → Bosch; ceased production
• Bausch & Lomb; ceased production
• Bell & Howell / TDC, US: "Headliner"; ceased production
• Braun AG, Germany: "D", "PA"; ceased production
• Braun Foto Technik, Germany: "Paximat", "Multimag" → Reflecta
• VEB DEFA, Germany: "Filius"→ VEB Gerätewerk Friedrichshagen: "Filius"; ceased production
• Eastman Kodak (–2004): "Carousel-S", "Ektagraphic", "Ektapro" → Leica
• Elmo, Japan
• Enna, Germany; ceased production
• Erno Photo, Germany; ceased production
• VEB Feinmess, Germany; ceased production
• Filmoli, Germany → Gebr. Martin, Germany; ceased production
• Foto Quelle, Germany: "Revue"; ceased distribution
• GAF, US; ceased distribution
• Götschmann, Germany (1978–2009) → Gecko-Cam (2009–)
• Hasselblad, Sweden; ceased production
• HASPE, Germany; ceased production
• Hähnel, Germany; ceased production
• Inox, France: "Prestige" → Prestinox
• Kindermann, Germany: "Diafocus" → Leica
• Leitz, Germany (1958–): "Prado" → Leica Projektion GmbH Zett Gerätewerk, Germany (1990–2004): "Pradovit", "Pradovit RT" → Leica Camera, Germany (2004–2006): "Pradovit"; ceased production
• Liesegang, Germany: "Fantax", "Diafant", "Fantimat"; ceased production
• Malinski, Germany: "Prokyon", "Malicolor" → Pentacon
• Minolta, Japan; ceased production
• Minox, Germany: "Minomat"; ceased production
• Navitar, US
• Nikon, Japan; ceased production
• Ernst Plank, Germany: "Noris", "Trumpf"; ceased production
• Pentacon, Germany: "Aspectar", "Malicolor"; ceased production
• Asahi Pentax, Japan; ceased production
• Prestinox, France → Plawa Condor (1969–?); ceased production
• Pouva, Germany; ceased production
• RBT, Germany
• Queen, Germany: "Automat"; ceased distribution
• Reflecta, Germany: "Multimag"
• Rollei, Germany (1960–2007): "Rolleiscop", "Rolleivision" → Franke & Heidecke, Germany (2007–2009): "Rolleivision" → DHW Fototechnik, Germany (2009–2015): "Rolleivision"; ceased production
• Royal, Germany?; ceased distribution
• Sankyo, Japan; ceased production
• Sawyer's, US; company sold to GAF
• Silma, Italy → Bauer and Rollei; ceased production
• TAV Simda
• Vicom
• Vivitar, US
• Voigtländer, Germany: "Perkeo" → Zett
• Zeiss Ikon, Germany (1964/1969–): "Ikolux" → Zett
• Zeiss Jena, Germany → Pentacon, Germany
• Zett, Germany (1928–1989): "Fafix", "Zett", "Zettomat", "Perkeo" → Leica Projektion GmbH Zett Gerätewerk, Germany (1990–2004)
• CBИTЯ3ъ, Russia: "ABTO"; ceased production

See also

• Slide viewer
• Carousel slide projector
• Presentation slide

References

General references

• Murphy, Burt (February 1973). Slide projectors get smarter all the time. Popular Mechanics. Retrieved 2011-10-22.