Editing Slide projector (section)

===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.