slide projector

File:Continuous-Slide Lantern.jpg|Continuous-Slide Lantern, {{circa|1881}}

File:Kodak Carousel 4400 projector with 140-slide tray.jpg|A Kodak Carousel model 4400 slide projector, first sold in the mid-1980s

File:Pet Projector (5366333065).jpg|Self-contained slide projector with rear-projection screen and carousel tray

A continuous-slide lantern was patented in 1881.{{cite book|title=The Canadian Patent Office Record and Mechanics' Magazine, Volume 9|year=1881|url=https://books.google.com/books?id=4FNGAQAAMAAJ&q=Continuous-Slide+Lantern.&pg=RA2-PA169}} It included a dissolving views apparatus.Sloane, T. O'Conor. Facts Worth Knowing Selected Mainly from the Scientific American for Household, Workshop, and Farm Embracing Practical and Useful Information for Every Branch of Industry. Hartford: S. S. Scranton & Co. 1895.

File:Diaprojektor beleuchtungssystem IMGP1044.jpg, 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:{{cite magazine |url=https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38 |title=Try Projection! |first=Robert |last=Beeler |date=October 1990 |magazine=Popular Photography |pages=38–47;160–161 |access-date=2 September 2024}}{{rp|39–40}}

• 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

Most slide projectors have a mechanism to hold slides in place during projection; many feature automated or mechanized slide advance and return to facilitate slideshows with multiple images.

File:Braun Camera-Werk Novamat M 330 - Philips halogen lamp-2203.jpg 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).{{Cite web|url=http://www.pradoseum.eu/Literatur/pradovit-rc-74.pdf|title=Pradovit RV-74 projector manual|publisher=Leitz|date=September 1972}}

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.{{cite web |url=https://archive.org/details/kodak-ektagraphic-e-2-slide-projector-manual-1970s/ |title=Kodak Ektagraphic Slide Projector, Model E-2 |publisher=Eastman Kodak |date=May 1975 |access-date=30 August 2024}}{{rp|10}} Some slide projectors used bulbs that had an integral multifaceted reflector, which were more expensive than bare bulbs, but were more convenient to use, as the reflector did not have to be adjusted after bulb changes.{{rp|43}}

File:Zeiss Ikon Slide projectors Royal AF selektiv AV Diaprojektor Duo 03.jpg brand, uses a straight-through tray; a thin arm grabs slides from a tray and puts them into the light path; the tray is advanced along its length. 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.{{rp|3}}{{cite web |url=https://archive.org/details/cbpf_000213/page/n17/mode/2up |title=GK Delineascope Reference Manual |publisher=American Optical Corporation |date=September 1968 |access-date=30 August 2024}}

Standard focal lengths for projector lenses are approximately twice that of a normal lens for that film format, which allows the projector to be located behind the audience for an average screen size. For example, with 135 film, a standard projector lens focal length would be around 100 mm.{{rp|41}} Starting in the 1970s, some slide projectors were offered with autofocus to compensate for differences in slide mount thickness or warping.{{cite web |url=https://www.pacificrimcamera.com/rl/03480/03480.pdf |title=Rollei slide projectors (dealer catalog) |date=1978 |publisher=Rollei |access-date=2 September 2024 |via=Pacific Rim Camera, Reference Library}}

Alternatively, the image may be projected onto a translucent "rear projection" screen, often used for continuous automatic display for close viewing. For example, the Singer Caramate and Bell & Howell RingMaster projected slides onto a flat screen approximately the size and shape of a small CRT TV;{{cite web |url=https://www.retrothing.com/2007/08/singer-caramate.html |title=Singer Caramate II SP: Multimedia Slide Projector |author=bohus |date=August 23, 2007 |website=Retro Thing |access-date=2 September 2024}}{{cite web |url=https://www.radiomuseum.org/r/bell_howel_ringmaster_soundslide_projector_797c.html |title=RingMaster |website=Radio Museum |access-date=30 August 2024}} the RingMaster also could be used for front projection for larger audiences.{{cite magazine |url=https://books.google.com/books?id=xB0DAAAAMBAJ&pg=PA24 |title=Get the picture two ways with one sound-slide projector [advertisement] |date=May 1978 |page=24 |magazine=Cincinnati Magazine |access-date=30 August 2024}} 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.{{fact|date=September 2022}}

File:60 CARRUSEL.jpg Carousel S-AV 1050, which features a horizontal rotary slide tray]]

Some slide projectors required users to manually place each slide that was being shown.{{cite web |url=https://archive.org/details/pp-46-9-23 |title=To do a slide justice ... show it with an Argus projector [advertisement] |publisher=Argus Camera Corporation |date=September 1946 |access-date=30 August 2024}} 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. Some automated slide projectors offered slide trays with straight, rectangular shapes,{{cite news |url=https://www.nytimes.com/2013/01/21/arts/design/its-a-spaceship-no-its-a-time-machine.html |title=It's a Spaceship! No, It's a Time Machine |first=Alice |last=Rawsthron |date=January 20, 2013 |work=The New York Times |access-date=30 August 2024}} which were popular in Europe; these use an arm, moving laterally, to extract a slide from the cartridge for projection.{{rp|42}} Some straight-tray machines could also accept vertical rotary cartridges, which resemble a Ferris wheel.{{rp|42}} In the United States, Eastman Kodak introduced Carousel slide projectors in 1961, which used a horizontal rotary cartridge like the namesake merry-go-round, and the format soon became ubiquitous there.{{cite magazine |url=https://edtechmagazine.com/higher/article/2016/09/kodak-carousel-projectors-revolutionized-lecture |title=Kodak Carousel Projectors Revolutionized the Lecture |first=Meghan Bogardus |last=Cortez |date=September 26, 2016 |magazine=EdTech |access-date=30 August 2024}} Advantages of Carousel-type slide projectors include a simpler, gravity-fed mechanism, and the ability to automatically repeat the sequence of images without having to reload;{{rp|41}} however, the circular trays tended to be bulkier and more expensive.{{rp|42}}

Sophisticated transition effects between images, such as dissolves, can be performed with multiple projectors; Rollei introduced the P3800 at photokina 1976, which had two lenses and could perform without an additional unit. By 1990, Rollei marketed the Rolleivision 35 Twin Digital, an upgraded P3800 which added a personal computer interface to control its operation.{{rp|47}} However, competing technologies which used images directly displayed from computers, such as projection panels and video projectors, largely displaced film slide projectors by the mid-1990s.

Slide projectors proper:

• Straight-tray slide projectors have a straight magazine holding several slides.{{fact|date=September 2022}}
• Carousel slide projectors have a circular magazine holding several slides.
• Stack-loader slide projectors{{fact|date=September 2022}}
• Bell & Howell Slide Cube Projector had a cube-shaped magazine holding several slides.
• Dual slide projectors{{fact|date=September 2022}}
• Single slide projectors project a single slide at a time, changed by the operator.{{fact|date=September 2022}}
• Dissolve projectors{{fact|date=September 2022}}
• Stereo slide projectors project two slides simultaneously with different polarizations, making slides appear as three-dimensional to viewers wearing polarizing glasses{{fact|date=September 2022}}
• Medium-format slide projectors, for medium-format slides larger than 35mm.{{fact|date=September 2022}}
• Specialised large-format slide projectors for large transparencies of 18 × 18 cm (7.1 × 7.1") or larger.{{fact|date=April 2024}}

Related devices:

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

List of known manufacturers of slide projectors:

• Agfa Gevaert, Germany (–1984) → Reflecta (1984–)
• {{Interlanguage link multi|Bauer (company)|de|3=Eugen Bauer (Unternehmen)|lt=Bauer}}, Germany → Bosch; ceased production{{fact|date=September 2022}}
• 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{{fact|date=September 2022}}
• 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–){{fact|date=September 2022}}
• Hasselblad, Sweden; ceased production
• HASPE, Germany; ceased production
• Hähnel, Germany; ceased production
• Inox, France: "Prestige" → Prestinox
• {{Interlanguage link multi|Kindermann (company)|de|3=Kindermann GmbH|lt=Kindermann}}, Germany: "Diafocus" → Leica{{fact|date=September 2022}}
• Leitz, Germany (1958–): "Prado" → Leica Projektion GmbH Zett Gerätewerk, Germany (1990–2004): "Pradovit", "Pradovit RT" → Leica Camera, Germany (2004–2006): "Pradovit"; ceased production{{fact|date=September 2022}}
• {{Interlanguage link multi|Liesegang|de|3=Liesegang (Unternehmen)|lt=Liesegang}}, Germany: "Fantax", "Diafant", "Fantimat"; ceased production
• Malinski, Germany: "Prokyon", "Malicolor" → Pentacon
• Minolta, Japan; ceased production
• Minox, Germany: "Minomat"; ceased production
• Navitar, US{{fact|date=September 2022}}
• 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{{fact|date=September 2022}}
• Pouva, Germany; ceased production
• RBT, Germany
• Queen, Germany: "Automat"; ceased distribution
• Reflecta, Germany: "Multimag"{{fact|date=September 2022}}
• 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
• {{Interlanguage link multi|Silma|it}}, Italy → Bauer and Rollei; ceased production{{fact|date=September 2022}}
• {{Interlanguage link multi|Simda|fr|3=Simda|lt=TAV Simda}}{{fact|date=September 2022}}
• Vicom{{fact|date=September 2022}}
• Vivitar, US
• Voigtländer, Germany: "Perkeo" → Zett
• Zeiss Ikon, Germany (1964/1969–): "Ikolux" → Zett
• Zeiss Jena, Germany → Pentacon, Germany{{fact|date=September 2022}}
• Zett, Germany (1928–1989): "Fafix", "Zett", "Zettomat", "Perkeo" → Leica Projektion GmbH Zett Gerätewerk, Germany (1990–2004)
• CBИTЯ3ъ, Russia: "ABTO"; ceased production{{fact|date=September 2022}}

• Slide viewer
• Carousel slide projector
• Presentation slide

• {{cite book|title=Slide projectors get smarter all the time|url=https://books.google.com/books?id=GtUDAAAAMBAJ&q=slide+projector&pg=PA140|date=February 1973|publisher=Popular Mechanics|access-date=2011-10-22|first=Burt|last=Murphy}}

{{reflist}}

{{Display technology}}

{{Photography}}

{{Authority control}}

Category:Display devices

de:Projektor#Durchlichtprojektion