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Slide projector
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<h2 id="history">History</h2> <p>A continuous-slide lantern was patented in 1881.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> It included a <a href="/facts/Dissolving_views/Y12qd7BN">dissolving views</a> apparatus.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p> <h2 id="design">Design</h2> <p>A projector has three main optical elements:<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>: 39–40 </p> <ul><li>high <a href="/facts/Luminous_flux/Sfya3RXh">luminous flux</a> electric <a href="/facts/Incandescent_light_bulb/31frjg0A">incandescent light bulb</a> or other light source, usually fan-cooled</li> <li>reflector and <a href="/facts/Condenser_(optics)/l4MRBDDK">condenser lens system</a> to direct the light through the slide</li> <li>focusing projection <a href="/facts/Lens_(optics)/ejlH6n5c">lens</a></li></ul> <p>Most slide projectors have a mechanism to hold slides in place during projection; many feature automated or mechanized slide advance and return to facilitate <a href="/facts/Slideshow/rB9Jw2w8">slideshows</a> with multiple images. </p> <h3>Light source and collimation</h3> <p>An <a href="/facts/Incandescent_lamp_bulb/31frjg0A">incandescent lamp bulb</a> is used to generate light, usually specially designed to have a small, bright <a href="/facts/Electrical_filament/31frjg0A">filament</a> to produce a sharp and bright image. For example, the <a href="/facts/Ernst_Leitz_GmbH/MHdUdH6H">Leitz</a> 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).<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p><p>Light from the bulb is modified from a point source by reflection and passing through condenser lens(es) to generate a <a href="/facts/Collimated_beam/lhd2hhPt">collimated beam</a>, 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 <a href="/facts/Infrared/44XdJNcc">infrared</a>.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>: 10 Some slide projectors used bulbs that had an integral <a href="/facts/Multifaceted_reflector/ff5HIUeB">multifaceted reflector</a>, 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.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>: 43 </p> <h3>Projection</h3> <p>After the collimated beam passes through the <a href="/facts/Transparent_materials/PRryNNW6">transparent</a> slide, it is enlarged by a projection lens onto a flat <a href="/facts/Projection_screen/EfJYBwt2">projection screen</a> 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.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a>: 3 <a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p><p>Standard <a href="/facts/Focal_length/brGIUkEY">focal lengths</a> for projector lenses are approximately twice that of a <a href="/facts/Normal_lens/HTqmyveN">normal lens</a> for that <a href="/facts/Film_format/hoH7lLa3">film format</a>, which allows the projector to be located behind the audience for an average screen size. For example, with <a href="/facts/135_film/UWGpI8k5">135 film</a>, a standard projector lens focal length would be around 100 mm.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>: 41 Starting in the 1970s, some slide projectors were offered with <a href="/facts/Autofocus/1B0tQWg2">autofocus</a> to compensate for differences in slide mount thickness or warping.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p><p>Alternatively, the image may be projected onto a translucent "rear projection" screen, often used for continuous automatic display for close viewing. For example, the <a href="/facts/Singer_Corporation/lFrnG7qa">Singer</a> <i>Caramate</i> and <a href="/facts/Bell_%2526_Howell/LDjDqQTh">Bell & Howell</a> <i>RingMaster</i> projected slides onto a flat screen approximately the size and shape of a small CRT TV;<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a><a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> the RingMaster also could be used for front projection for larger audiences.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> 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. </p> <h3>Mechanical</h3> <p>Some slide projectors required users to manually place each slide that was being shown.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> 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,<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> which were popular in Europe; these use an arm, moving laterally, to extract a slide from the cartridge for projection.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a>: 42 Some straight-tray machines could also accept vertical rotary cartridges, which resemble a <a href="/facts/Ferris_wheel/CSsDYVXl">Ferris wheel</a>.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a>: 42 In the United States, Eastman Kodak introduced <a href="/facts/Carousel_slide_projector/msqqwaCI">Carousel slide projectors</a> in 1961, which used a horizontal rotary cartridge like the namesake <a href="/facts/Merry-go-round/FSs5Nz0H">merry-go-round</a>, and the format soon became ubiquitous there.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> 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;<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a>: 41 however, the circular trays tended to be bulkier and more expensive.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a>: 42 </p><p>Sophisticated <a href="/facts/Film_transition/cWPXqWTF">transition effects between images</a>, such as <a href="/facts/Dissolve_(filmmaking)/AovejGyp">dissolves</a>, can be performed with multiple projectors; <a href="/facts/Rollei/sannXhNC">Rollei</a> introduced the P3800 at <a href="/facts/Photokina/bllMCkzp">photokina</a> 1976, which had two lenses and could perform without an additional unit.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> By 1990, <a href="/facts/Rollei/sannXhNC">Rollei</a> marketed the Rolleivision 35 Twin Digital, an upgraded P3800 which added a personal computer interface to control its operation.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a>: 47 However, competing technologies which used images directly displayed from computers, such as <a href="/facts/Projection_panel/X4X8hxNC">projection panels</a> and <a href="/facts/Video_projector/5fIVG2sq">video projectors</a>, largely displaced film slide projectors by the mid-1990s. </p> <h2 id="types">Types</h2> <p>Slide projectors proper: </p> <ul><li>Straight-tray slide projectors have a straight magazine holding several slides.</li> <li><a href="/facts/Carousel_slide_projector/msqqwaCI">Carousel slide projectors</a> have a circular magazine holding several slides.</li> <li>Stack-loader slide projectors</li> <li><a href="/facts/Bell_%2526_Howell/LDjDqQTh">Bell & Howell</a> <a href="/facts/Slide_Cube_Projector/AFqSAVwa">Slide Cube Projector</a> had a cube-shaped magazine holding several slides.</li> <li>Dual slide projectors</li> <li>Single slide projectors project a single slide at a time, changed by the operator.</li> <li>Dissolve projectors</li> <li>Stereo slide projectors project two slides simultaneously with different <a href="/facts/Polarization_(waves)/fP33m0eD">polarizations</a>, making slides appear as three-dimensional to viewers wearing polarizing glasses</li> <li>Medium-format slide projectors, for <a href="/facts/Medium-format/gWghbVj9">medium-format</a> slides larger than 35mm.</li> <li>Specialised <a href="/facts/Large-format_slide_projector/k5Ubargm">large-format slide projectors</a> for large transparencies of 18 × 18 cm (7.1 × 7.1") or larger.</li></ul> <p>Related devices: </p> <ul><li><a href="/facts/Overhead_projector/M8V2Y4xa">Overhead projectors</a>, for page-sized transparencies</li> <li><a href="/facts/Slide_viewer/tmMW3LBT">Slide viewer</a>, for direct viewing of a magnified image of a slide</li></ul> <h2 id="manufacturers">Manufacturers</h2> <p>List of known manufacturers of slide projectors: </p> <ul><li><a href="/facts/Agfa/TNsfjVuj">Agfa</a> Gevaert, Germany (–1984) → Reflecta (1984–)</li> <li>Bauer [de], Germany → <a href="/facts/Robert_Bosch_GmbH/wPuk1Udv">Bosch</a>; ceased production</li> <li><a href="/facts/Bausch_%2526_Lomb/pDoWkovR">Bausch & Lomb</a>; ceased production</li> <li><a href="/facts/Bell_%2526_Howell/LDjDqQTh">Bell & Howell</a> / TDC, US: "Headliner"; ceased production</li> <li><a href="/facts/Braun_(company)/NTkaUcex">Braun AG</a>, Germany: "D", "PA"; ceased production</li> <li><a href="/facts/Carl_Braun_Camera-Werk/esHQDuxF">Braun Foto Technik</a>, Germany: "<a href="/facts/Paximat/esHQDuxF">Paximat</a>", "<a href="/facts/Multimag/esHQDuxF">Multimag</a>" → Reflecta</li> <li>VEB DEFA, Germany: "Filius"→ VEB Gerätewerk Friedrichshagen: "Filius"; ceased production</li> <li><a href="/facts/Eastman_Kodak/zMnK74Cp">Eastman Kodak</a> (–2004): "Carousel-S", "Ektagraphic", "Ektapro" → Leica</li> <li><a href="/facts/Elmo_(company)/BlRaqCr2">Elmo</a>, Japan</li> <li>Enna, Germany; ceased production</li> <li>Erno Photo, Germany; ceased production</li> <li>VEB Feinmess, Germany; ceased production</li> <li>Filmoli, Germany → Gebr. Martin, Germany; ceased production</li> <li><a href="/facts/Foto_Quelle/AE4566eH">Foto Quelle</a>, Germany: "Revue"; ceased distribution</li> <li><a href="/facts/GAF_Materials_Corporation/VrSGvm7N">GAF</a>, US; ceased distribution</li> <li>Götschmann, Germany (1978–2009) → Gecko-Cam (2009–)</li> <li><a href="/facts/Hasselblad/RdXsvqzL">Hasselblad</a>, Sweden; ceased production</li> <li>HASPE, Germany; ceased production</li> <li>Hähnel, Germany; ceased production</li> <li>Inox, France: "Prestige" → Prestinox</li> <li>Kindermann [de], Germany: "Diafocus" → Leica</li> <li><a href="/facts/Leica_Camera/kCdXV5jD">Leitz</a>, Germany (1958–): "Prado" → Leica Projektion GmbH Zett Gerätewerk, Germany (1990–2004): "Pradovit", "Pradovit RT" → Leica Camera, Germany (2004–2006): "Pradovit"; ceased production</li> <li><a href="/facts/Liesegang/NwcTvLgI">Liesegang</a> [de], Germany: "Fantax", "Diafant", "Fantimat"; ceased production</li> <li>Malinski, Germany: "Prokyon", "Malicolor" → Pentacon</li> <li><a href="/facts/Minolta/7Fxhx5df">Minolta</a>, Japan; ceased production</li> <li><a href="/facts/Minox/6YMn30uf">Minox</a>, Germany: "Minomat"; ceased production</li> <li>Navitar, US</li> <li><a href="/facts/Nikon/7yoQHTSe">Nikon</a>, Japan; ceased production</li> <li>Ernst Plank, Germany: "Noris", "Trumpf"; ceased production</li> <li><a href="/facts/Pentacon/88vcv8Xo">Pentacon</a>, Germany: "Aspectar", "Malicolor"; ceased production</li> <li><a href="/facts/Asahi_Pentax/mXMMxbjk">Asahi Pentax</a>, Japan; ceased production</li> <li>Prestinox, France → Plawa Condor (1969–?); ceased production</li> <li>Pouva, Germany; ceased production</li> <li>RBT, Germany</li> <li>Queen, Germany: "Automat"; ceased distribution</li> <li>Reflecta, Germany: "Multimag"</li> <li><a href="/facts/Rollei/sannXhNC">Rollei</a>, Germany (1960–2007): "<a href="/facts/Rolleiscop/sannXhNC">Rolleiscop</a>", "<a href="/facts/Rolleivision/sannXhNC">Rolleivision</a>" → <a href="/facts/Franke_%2526_Heidecke/sannXhNC">Franke & Heidecke</a>, Germany (2007–2009): "Rolleivision" → <a href="/facts/DHW_Fototechnik/sannXhNC">DHW Fototechnik</a>, Germany (2009–2015): "Rolleivision"; ceased production</li> <li>Royal, Germany?; ceased distribution</li> <li><a href="/facts/Sankyo_(camera_company)/lrg3993L">Sankyo</a>, Japan; ceased production</li> <li><a href="/facts/Sawyer%2527s/G1znjye2">Sawyer's</a>, US; company sold to GAF</li> <li>Silma [it], Italy → Bauer and Rollei; ceased production</li> <li>TAV Simda [fr]</li> <li>Vicom</li> <li><a href="/facts/Vivitar/lhERzJd4">Vivitar</a>, US</li> <li><a href="/facts/Voigtl%25C3%25A4nder/3jjq7cVj">Voigtländer</a>, Germany: "Perkeo" → Zett</li> <li><a href="/facts/Zeiss_Ikon/sCCBJNxV">Zeiss Ikon</a>, Germany (1964/1969–): "Ikolux" → Zett</li> <li>Zeiss Jena, Germany → Pentacon, Germany</li> <li><a href="/facts/Zett/EHRKG5A0">Zett</a>, Germany (1928–1989): "Fafix", "Zett", "Zettomat", "Perkeo" → Leica Projektion GmbH Zett Gerätewerk, Germany (1990–2004)</li> <li>CBИTЯ3ъ, Russia: "ABTO"; ceased production</li></ul> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Slide_viewer/tmMW3LBT">Slide viewer</a></li> <li><a href="/facts/Carousel_slide_projector/msqqwaCI">Carousel slide projector</a></li> <li><a href="/facts/Presentation_slide/3gHj8hdq">Presentation slide</a></li></ul> <h3>General references</h3> <ul><li>Murphy, Burt (February 1973). <a href="https://books.google.com/books?id=GtUDAAAAMBAJ&q=slide+projector&pg=PA140"><i>Slide projectors get smarter all the time</i></a>. <a href="/facts/Popular_Mechanics/AUHUPsqy">Popular Mechanics</a>. Retrieved 2011-10-22.</li></ul> <h3>Inline citations</h3> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>The Canadian Patent Office Record and Mechanics' Magazine, Volume 9. 1881. <a href="https://books.google.com/books?id=4FNGAQAAMAAJ&q=Continuous-Slide+Lantern.&pg=RA2-PA169" target="_blank">https://books.google.com/books?id=4FNGAQAAMAAJ&q=Continuous-Slide+Lantern.&pg=RA2-PA169</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Pradovit RV-74 projector manual" (PDF). Leitz. September 1972. <a href="http://www.pradoseum.eu/Literatur/pradovit-rc-74.pdf" target="_blank">http://www.pradoseum.eu/Literatur/pradovit-rc-74.pdf</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Kodak Ektagraphic Slide Projector, Model E-2". Eastman Kodak. May 1975. Retrieved 30 August 2024. <a href="https://archive.org/details/kodak-ektagraphic-e-2-slide-projector-manual-1970s/" target="_blank">https://archive.org/details/kodak-ektagraphic-e-2-slide-projector-manual-1970s/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Kodak Ektagraphic Slide Projector, Model E-2". Eastman Kodak. May 1975. Retrieved 30 August 2024. <a href="https://archive.org/details/kodak-ektagraphic-e-2-slide-projector-manual-1970s/" target="_blank">https://archive.org/details/kodak-ektagraphic-e-2-slide-projector-manual-1970s/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"GK Delineascope Reference Manual". American Optical Corporation. September 1968. Retrieved 30 August 2024. <a href="https://archive.org/details/cbpf_000213/page/n17/mode/2up" target="_blank">https://archive.org/details/cbpf_000213/page/n17/mode/2up</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"Rollei slide projectors (dealer catalog)" (PDF). Rollei. 1978. Retrieved 2 September 2024 – via Pacific Rim Camera, Reference Library. <a href="https://www.pacificrimcamera.com/rl/03480/03480.pdf" target="_blank">https://www.pacificrimcamera.com/rl/03480/03480.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>bohus (August 23, 2007). "Singer Caramate II SP: Multimedia Slide Projector". Retro Thing. Retrieved 2 September 2024. <a href="https://www.retrothing.com/2007/08/singer-caramate.html" target="_blank">https://www.retrothing.com/2007/08/singer-caramate.html</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"RingMaster". Radio Museum. Retrieved 30 August 2024. <a href="https://www.radiomuseum.org/r/bell_howel_ringmaster_soundslide_projector_797c.html" target="_blank">https://www.radiomuseum.org/r/bell_howel_ringmaster_soundslide_projector_797c.html</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"Get the picture two ways with one sound-slide projector [advertisement]". Cincinnati Magazine. May 1978. p. 24. Retrieved 30 August 2024. <a href="https://books.google.com/books?id=xB0DAAAAMBAJ&pg=PA24" target="_blank">https://books.google.com/books?id=xB0DAAAAMBAJ&pg=PA24</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"To do a slide justice ... show it with an Argus projector [advertisement]". Argus Camera Corporation. September 1946. Retrieved 30 August 2024. <a href="https://archive.org/details/pp-46-9-23" target="_blank">https://archive.org/details/pp-46-9-23</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Rawsthron, Alice (January 20, 2013). "It's a Spaceship! No, It's a Time Machine". The New York Times. Retrieved 30 August 2024. <a href="https://www.nytimes.com/2013/01/21/arts/design/its-a-spaceship-no-its-a-time-machine.html" target="_blank">https://www.nytimes.com/2013/01/21/arts/design/its-a-spaceship-no-its-a-time-machine.html</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Cortez, Meghan Bogardus (September 26, 2016). "Kodak Carousel Projectors Revolutionized the Lecture". EdTech. Retrieved 30 August 2024. <a href="https://edtechmagazine.com/higher/article/2016/09/kodak-carousel-projectors-revolutionized-lecture" target="_blank">https://edtechmagazine.com/higher/article/2016/09/kodak-carousel-projectors-revolutionized-lecture</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>"Rollei slide projectors (dealer catalog)" (PDF). Rollei. 1978. Retrieved 2 September 2024 – via Pacific Rim Camera, Reference Library. <a href="https://www.pacificrimcamera.com/rl/03480/03480.pdf" target="_blank">https://www.pacificrimcamera.com/rl/03480/03480.pdf</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>Beeler, Robert (October 1990). "Try Projection!". Popular Photography. pp. 38–47, 160–161. Retrieved 2 September 2024. <a href="https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38" target="_blank">https://books.google.com/books?id=qOIgD4S4RCQC&pg=PA38</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> </ol>