Editing Slide projector (section)

===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}}