Editing Slide projector

{{refimprove|date=September 2022}}
{{Short description|Opto-mechanical device for showing photographic slides}}
[[File:Projecteur de diapositives Prestinox début des années 1960.jpg|thumb|A 1960 slide projector]]

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

[[135 film|35&nbsp;mm]] slide projectors, direct descendants of the larger-format [[magic lantern]], first came into widespread use during the 1950s for [[slide show]]s as home entertainment, and for use by educational and other institutes. [[Reversal film]] created a small positive projectable image rather than the [[Negative (photography)|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Photographic film slides and projectors have been replaced by [[image file]]s on [[digital storage media]] shown on a projection screen by using a [[video projector]], or displayed on a large-screen video [[Computer monitor|monitor]].

== History ==
<gallery heights=150px widths=200px>
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
</gallery>
A continuous-slide lantern was patented in 1881.<ref>{{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}}</ref> It included a [[dissolving views]] apparatus.<ref>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.</ref>

==Design==
[[File:Diaprojektor beleuchtungssystem IMGP1044.jpg|thumb|right|upright=1.5|Slide projector light generation and collimation system: from left to right, [[Parabolic reflector|mirror / reflector]], [[Halogen lamp|bulb]], [[Condenser (optics)|condenser lens]] 1, green-tinted [[Hot mirror|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:<ref name=PopPhoto-9010>{{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}}</ref>{{rp|39–40}}
* high [[luminous flux]] electric [[incandescent light bulb]] or other light source, usually fan-cooled
* reflector and [[Condenser (optics)|condenser lens system]] to direct the light through the slide
* focusing projection [[lens (optics)|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 [[slideshow]]s with multiple images.

===Light source and collimation===
[[File:Braun Camera-Werk Novamat M 330 - Philips halogen lamp-2203.jpg|thumb|left|[[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 [[Electrical filament|filament]] to produce a sharp and bright image. For example, the [[Ernst Leitz GmbH|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).<ref>{{Cite web|url=http://www.pradoseum.eu/Literatur/pradovit-rc-74.pdf|title=Pradovit RV-74 projector manual|publisher=Leitz|date=September 1972}}</ref>

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]].<ref name=Kodak-E2>{{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}}</ref>{{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.<ref name=PopPhoto-9010/>{{rp|43}}

===Projection===
[[File:Zeiss Ikon Slide projectors Royal AF selektiv AV Diaprojektor Duo 03.jpg|thumb|right|upright=1.3|This slide projector, sold under the [[Zeiss Ikon]] 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 materials|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.<ref name=Kodak-E2/>{{rp|3}}<ref>{{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}}</ref>

Standard [[focal length]]s 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&nbsp;mm.<ref name=PopPhoto-9010/>{{rp|41}} Starting in the 1970s, some slide projectors were offered with [[autofocus]] to compensate for differences in slide mount thickness or warping.<ref name=Rollei78>{{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}}</ref>

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 Corporation|Singer]] ''Caramate'' and [[Bell & Howell]] ''RingMaster'' projected slides onto a flat screen approximately the size and shape of a small CRT TV;<ref>{{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}}</ref><ref>{{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}}</ref> the RingMaster also could be used for front projection for larger audiences.<ref>{{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}}</ref> 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}}

===Mechanical===
[[File:60 CARRUSEL.jpg|thumb|left|[[Kodak]] [[Carousel slide projector|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.<ref>{{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}}</ref> 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,<ref>{{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}}</ref> which were popular in Europe; these use an arm, moving laterally, to extract a slide from the cartridge for projection.<ref name=PopPhoto-9010/>{{rp|42}} Some straight-tray machines could also accept vertical rotary cartridges, which resemble a [[Ferris wheel]].<ref name=PopPhoto-9010/>{{rp|42}} In the United States, Eastman Kodak introduced [[Carousel slide projector]]s in 1961, which used a horizontal rotary cartridge like the namesake [[merry-go-round]], and the format soon became ubiquitous there.<ref>{{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}}</ref> 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;<ref name=PopPhoto-9010/>{{rp|41}} however, the circular trays tended to be bulkier and more expensive.<ref name=PopPhoto-9010/>{{rp|42}}

Sophisticated [[film transition|transition effects between images]], such as [[Dissolve (filmmaking)|dissolve]]s, can be performed with multiple projectors; [[Rollei]] introduced the P3800 at [[photokina]] 1976, which had two lenses and could perform without an additional unit.<ref name=Rollei78/> By 1990, [[Rollei]] marketed the Rolleivision 35 Twin Digital, an upgraded P3800 which added a personal computer interface to control its operation.<ref name=PopPhoto-9010/>{{rp|47}} However, competing technologies which used images directly displayed from computers, such as [[projection panel]]s and [[video projector]]s, largely displaced film slide projectors by the mid-1990s.

==Types==

Slide projectors proper:
* Straight-tray slide projectors have a straight magazine holding several slides.{{fact|date=September 2022}}
* [[Carousel slide projector]]s 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 [[Polarization (waves)|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 projector]]s for large transparencies of 18 × 18&nbsp;cm (7.1 × 7.1") or larger.{{fact|date=April 2024}}

Related devices:
* [[Overhead projector]]s, 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–)
* {{Interlanguage link multi|Bauer (company)|de|3=Eugen Bauer (Unternehmen)|lt=Bauer}}, Germany → [[Robert Bosch GmbH|Bosch]]; ceased production{{fact|date=September 2022}}
* [[Bausch & Lomb]]; ceased production
* [[Bell & Howell]] / TDC, US: "Headliner"; ceased production
* [[Braun (company)|Braun AG]], Germany: "D", "PA"; ceased production
* [[Carl Braun Camera-Werk|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 (company)|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 Materials Corporation|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}}
* [[Leica Camera|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 (camera company)|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}}

==See also==
* [[Slide viewer]]
* [[Carousel slide projector]]
* [[Presentation slide]]

==References==
===General references===
* {{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}}

===Inline citations===
{{reflist}}


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[[Category:Slide projectors| ]]
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