Over head projector in procedure during a class training
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Anoverhead projector (OHP)is certainly a variant of slide projector that is usually used to screen images to an viewers.12.
Just like smartphones and tablets, interactive projectors use multi-touch, meaning multiple students can complete a puzzle together. There are two options here.
- 1Optical program
Optical systemedit
An over head projector works on the same principle as a 35mmichael slide projéctor, in which á focusing lens tasks light from an lighted slide onto a projection display screen where a actual image is usually formed. However some variations are usually necessitated by the much larger size of the transparencies used (usually the dimension of a printed page), and the necessity that the openness be positioned face up (and readabIe to the speaker). For the second option purpose, the projector consists of a looking glass simply before or after the concentrating zoom lens to fold the optical system toward the side to side. That reflection also accomplishes a reversal of the picture in order that the image projected onto the display corresponds to that óf the slide ás observed by the speaker looking straight down at it, rather than a hand mirror picture thereof. Therefore, the transparency is positioned face up (toward the match and focusing lens), in contrast with a 35mm slide projector or film projector (which lack such a looking glass) where the slide'beds image is usually non-reversed on the aspectoppositethe concentrating zoom lens.
The device has occasionally been known as a 'Belshazzar', after Belshazzar's party ('In the same hour arrived forth fingers of a guy's hand, and published over against thé candlestick upon thé plaister of thé wall structure of the king's palace: and the master saw the component of the hands that composed' (Daniel 5:5)).3
Condenseredit
Because the focusing lens (typically much less than 10 cm 4 in inside diameter) will be much smaller sized than the openness, a important role is played by the opticaI condenser which iIluminates the transparency. Since this demands a large optical lens (at least the size of the openness) but may end up being of bad optical high quality (since the sharpnéss of the picture does not rely on it), a Fresnel lens is employed. The Fresnel lens is located at (or is component of) the cup plate on which the openness is positioned, and serves to refocus most of the lighting hitting it into á converging cone tóward the concentrating lens. Without such a condenser at that stage, many of the light would miss the centering zoom lens (or it would possess to become really large and prohibitively expensive). Moreover, showcases or various other condensing elements below the Fresnel lens serve to raise the part of the lighting light bulb's output which gets to the Fresnel lens in the initial location. In order to offer sufficient lighting on the screen, a higher intensity light bulb is usually used which must become lover cooled.
Focus adjustment edit
Overhead projectors normally consist of a manual focusing system which raises and lowers the place of the centering zoom lens (including the folding reflection) in order to adapt the item distance (optical distance between the sIide and the lens) to focus at the chosen image length (length to the projection screen) given the set focal length of the concentrating zoom lens. This allows a range of projection distances.
Growing (or decreasing) the projection distance boosts (or reduces) the focusing system's magnification in order to fit the projection display screen in use (or occasionally just to accommodate the space set up). Boosting the projection length also means that the exact same quantity of lighting is spread over a larger screen, resulting in a dimmer image. With a change in the projection range, the focusing must be readjusted for a sharpened image. Nevertheless, the condensing optics (Fresnel lens) is certainly optimized for one particular vertical place of the lens, corresponding to one projection distance. Thus, when it is certainly concentrated for a significantly different projection length, component of the lighting cone projected by the Fresnel lens towards the centering lens misses that lens. This has the greatest impact towards the outer sides of the forecasted image, therefore that one generally sees possibly glowing blue or brownish fringing at the advantage of the display screen when the focus is definitely towards an extreme. Using the projector near its suggested projection distance enables a concentrating placement where this can be avoided and the intensity across the display is around consistent.
Source of illumination edit
Thé light technology of an over head projector is usually typically extremely simple compared to a contemporary LCD or DLP video projector. Many overheads use an extremely high-power halogen light fixture that may consume up to 750 watts. A high-flow blower is needed to maintain the light bulb from melting owing to the temperature generated, and this blowing apparatus is frequently on a timer that keeps it running for a time period after the light is definitely extinguished.
Further, the intensive high temperature accelerates failure of the high intensity light, often burning up out in much less than 100 hours, requiring replacing. In contrast, a contemporary LCD or DLP projector uses an arch light fixture which has a increased luminous efficiency and can last for thousands of hours. A drawback of that technologies is the comfortable up time required for arc lights.
Older overhead projectors used á tubular quartz bulb which has been mounted above a bowl-shaped refined reflector. However, because the light fixture was hanging above and outside the mirror, a large quantity of light was toss to the edges inside the projector body that has been wasted, thus requiring a increased power light for adequate screen illumination. More contemporary overhead projectors make use of an included light fixture and conical reflector assembly, allowing the lamp to become located heavy within the mirror and delivering a better part of its lighting towards the Fresnel lens; this allows making use of a lower power lamp for the exact same screen illumination.
A useful creativity for overhead projectors with integrated lamps/reflectors is the quick-swáp dual-lamp handle, allowing two lights to end up being set up in the projector in removable sockets. If one light fixture falls flat during a presentation the presenter can merely move a lever to slide the extra into place and keep on with the demonstration, without needing to open up the projection device or waiting around for the failed light bulb to interesting before changing it.
History edit
Somé historic projectors like the magic lantern can end up being considered as predecessors of the overhead projector. The steganographic reflection possibly emerged closest to how the over head projector has been used.
A language like german Jesuit college student Athanasius Kircher's 1645 publicationArs Mágna Lucis et Umbraéincluded a explanation of his creation, the 'Steganographic Reflection': a ancient projection system with a concentrating zoom lens and text message or images colored on a concave match reflecting sunlight, mostly meant for long distance conversation.4In 1654 Belgian Jesuit mathematician André Tacquet used Kircher'h technique to show the journey from China and taiwan to Belgium of Italian language Jesuit missionary Martinó Martini.5It will be unfamiliar how precisely Tacquet used Kircher'h system, but it will be possible that he came images on the projecting mirror while information of the journey were described.
German physicist Edmund Becquerel created the first known over head projection equipment in 1853. It has been exhibited by Norwegian instrument machine and creator Jules Dubóscq in 1866.67
An over head projector created by Us scientist Holly Morton has been marketed around 1880 as a 'top to bottom lantern'.8
The use of transparent bed linens for overhead projection, called viewfoils or viewgraphs, had been largely developed in the United Claims.
Overhead projectors were presented into U.S. armed service training during Planet Battle II. After the war they were used at academic institutions like the U.H. Army Academy.9
Over head projectors were used early on for law enforcement work with a cellophane roll over a 9-in . stage, allowing faciaI characteristics to bé rolled across thé stagé.citation needed
As thé need for projectors grew, Buhl Industries was launched in 1953, and grew to become the leading US factor for several optical refinements for the over head projector and its projection lens.citation needed
Over head projectors began to become widely used in universities and companies in the past due 1950s and early 1960s.quotation needed
ln the late 1950s Roger Appeldorn has been challenged by his employer at 3M to find a make use of for the transparencies that had been the waste materials of their colour copy procedure. Appeldorn developed a procedure for the projection of clear bed sheets that led to 3M's first marketable transparency movie. The Strategic Atmosphere Command bottom in Omaha had been one of the very first big customers, making use of circa 20,000 sheets per 30 days. 3M after that made a decision to develop their personal overhead projector rather of the a single they experienced been promoting until after that, which had been produced by an outdoors producer. It required many prototypes before á cost-effective, small and foldable version could become offered on Jan 15, 1962. It experienced a brand-new fresnel lens produced with a structured-surface plastic material, much better than some other plastic lenses and significantly cheaper than glass.10
In 1957, the United Areas' very first Federal Help to Training program triggered overhead sales which stayed higher up to the past due 1990s and into the 21scapital t One hundred year.quotation needed
Make use of in educationedit
The overhead projector facilitates an simple low-cost interactive environment for educators. Teaching materials can be pre-printed on plastic bedding, upon which the educator can straight write using a non-permanent, washable colour marking pen. This will save time, since the openness can end up being pre-printed and used repetitively, rather than getting materials composed by hand before each course.
The overhead is usually positioned at a comfy writing elevation for the instructor and enables the educator to face the class, facilitating better communication between the college students and teacher. The enlarging functions of the projector permit the educator to create in a comfortable small screenplay in a organic writing placement rather than creating in an excessively large script on a blackboard and having to continuously keep their arm out in midair to write on the bIackboard.
Whén the openness sheet is certainly complete of written or drawn material, it can merely be changed with a brand-new, fresh bed sheet with even more pre-printed materials, again conserving class period vs a bIackboard that would need to end up being erased and teaching components rewritten by the instructor. Right after the class time period, the transparencies are usually easily restored to their first unused condition by cleaning off with soap and drinking water.
LCD over head displays edit
ln the earlier 1980s-1990s, over head projectors had been used as component of a class computer display/projection system. A liquid-crystal section mounted in a plastic frame had been positioned on best of the over head projector and connected to the movie output of the computer, often dividing off the normal monitor output. A chilling enthusiast in the framework of the LCD cell would strike cooling surroundings across the LCD to avoid overheating that would fog the picture.
The 1st of these LCD panels were monochrome-only, and could screen NTSC movie output like as from an Apple company II personal computer or VCR. In the late 1980s color models became available, able of 'thousands' of colors (16-bit color), for the colour Macs and VGA Personal computers. The displays were never ever particularly fast to renew or revise, resulting in the sméaring of fast-móving images, but it was appropriate when nothing at all else had been obtainable.
Thé Do-It-YourseIf neighborhood has started using this concept to create low-cost home theatre projectors. By removing the casing and backlight set up of a common LCD keep track of, one can use the uncovered LCD display screen in conjunction with the over head projector to task the contents of the LCD screen to the walls at a much lower cost than with standard LCD projectors. Due to the mirróring of the picture in the head of the overhead projector, the image on the walls is usually 're-flipped' tó where it wouId end up being if one has been searching at the LCD display usually.
Decline in use edit
Overhead projectors were as soon as a common fixture in nearly all classrooms and business conference rooms, but today are gradually being changed by record cameras, devoted computer projection techniques and interactive whitéboards.citation needed Like systems allow the speaker to task video directly from a computer file, usually produced making use of software like as Microsoft PowérPoint and LibreOffice. Such sales pitches can also consist of animations, interactive elements, or even video videos, with simplicity of paging between photo slides. The relatively expensive printing or photocopying of color transparencies can be removed.
The principal reasondubiousfór this gradual replacement is usually the deeply ingrained use of computing technology in modern society and the incapacity of expenses to conveniently support the features that modern users need. While an overhead can display static images fairly properly, it works poorly at displaying moving pictures. The LCD video screen sections that had been as soon as used as án add-on tó an overhead projector have become outdated, with that mixture of screen technologies and projection optics right now optimally integrated into a contemporary video projector.
The specifications of customers have furthermore increasedquotation required, therefore that a poor, fuzzy over head projection that will be too brilliant in the center and as well dim around the edges is definitely no much longer appropriate. The optical focus, linearity, lighting and clarity of an over head generally cannot go with that of a video clip projectorquotation needed. Video clip projectors make use of extremely small picture generation mechanisms, enabling for accuracy opticssuspiciousthat much go beyond the plastic material fresnel zoom lens' optical overall performance. They also include additional optics that get rid of thehótspotin thé middle of the displayquotation neededstraight above the light source, therefore that the brightness is uniform almost everywhere on the projection display.
Criticswho? feel that there are some downsides as these technologies are more vulnerable to failure and have got a much steeper studying curve for the consumer than a regular overhead projector.
See also edit
Referralsedit
- ^Power, Stephen. ''The pedagogic excellence of the over head projector - ánd why interactive whitéboards alone received't ever match it''. Gathered9 Jan2018.
- ^Kavita, GU; Shashikala, G; Sreevidyalata, GM (2015). 'Use of Over Mind Projector for teaching and studying Good Needle Aspiration Cytology abilities to undergraduate learners and their belief'(PDF).Paper of Educational Research amp; Healthcare Instructor.3(1): 31-33.
- ^Willis, N. E. (13 Walk 2008). 'A Study of the Make use of of the Over head Projector in the United Kingdom'.Audio-Visual Press.3: 5-8. doi:10.1080/09523986908547852.
- ^Kircher, Athanasius (1645).Ars Magna Lucis et Umbrae. p. 912.
- ^'Para zeventiende eeuw. Jáargang 10' (in Nederlander and Latin).
- ^'Projectors and Slides'.
- ^'Over head Projectors'. National Museum of Us History. Gathered7 January2015.
- ^http://americanhistory.si.edu/mobilizing-minds/overhead-projectors
- ^A One hundred year of Invention - The 3M Sory(PDF).
- 501 Methods to Make use of the Over head Projectorby Lee Green (ISBN0-87287-339-0)
Outside links edit
Wikimédia Commons has media related toOver head projéctors. |
Gathered from 'https://en.wikipedia.org/watts/index.php?title=Overheadprojectoramp;oldid=886931990'
Christiaan Huygens's miraculous lantern was the earliest/oldest type of slide projector.
A 1960 slide projector
Light path
Aslide projectoris certainly an opto-mechanical device for showing photographicslides.
35 mm slide projectors, immediate descendants of the larger-format miracle lantern, very first arrived into widespread make use of during the 1950s as a type of periodic home enjoyment; family members and close friends would gather to watch slide exhibits. Reversal film was much in use, and provided slides snapped during holidays and at family members events. Slide projectors had been also widely used in academic and some other institutional configurations.
Final film glides and projectors possess mostly become changed by image data files on digital storage press proven on a projection display by making use of a movie projector or simply shown on a large-screen video monitor.
Backgroundedit
Continuous-Slide Lantern, ca. 1881
A continuous-slide lantern had been copyrighted in 1881.1It integrated a dissolving-view equipment.2
Elementsedit
A projector offers four major components:
- electrical incandescent lighting bulb or various other light source (usually fan-cooled)
- reflector and 'condensing' lens to steer the light to the slide
- slide owner
- concentrating lens
A flat piece of heat-absorbing glass is often placed in the light path between the condensing lens and the slide, to prevent damaging the second option. This cup transmits visible wavelengths but absorbs infrared. Lighting passes through the transparent slide and zoom lens, and the resulting picture is enlarged and projected onto a verticle with respect flat display screen so the viewers can see its representation. Additionally, the picture may become projected onto a clear 'rear projection' screen, usually used for continuous automatic screen for close up viewing. This type of projection furthermore avoids the target audience interrupting the light flow by throwing their shadows on the projection or by thumping into the projector.
Formsedit
- Individual slide projectors (manual type)
- Stereo slide projectors project two slides simultaneously with various polarizations, making slides show up as three-dimensional to viewers wearing polarizing glasses
- Large-format slide projectors for make use of on stages, at large events, or for new and marketing installations where high light result is required.
Producersedit
Checklist of known manufacturers of slide projectors:
- Agfa Gevaert, Germany (-1984) → Reflecta (1984-)
- Bauerde, Germany → Bosch; ceased production
- Bausch amp; Lomb; ceased production
- Bell amp; Howell / TDC, US: 'Headliner'; stopped production
- Braun AG, Indonesia: 'Chemical', 'PA'; ceased manufacturing
- Braun Foto Technik, Indonesia: 'Paximat', 'Multimag' → Reflecta
- VEB DEFA, Uk: 'Filius'→ VEB Gerätewerk Friedrichshagen: 'Filius'; stopped manufacturing
- Eastman Kodak (-2004): 'Carousel-S', 'Ektagraphic', 'Ektapro' → Leica
- Elmo, Japan
- Enna, Australia; ceased production
- Erno Photograph, Germany; stopped production
- VEB Feinmess, Philippines; ceased creation
- Filmoli, Indonesia → Gebr. Martin, Uk; ceased creation
- Foto Quelle, Indonesia: 'Revue'; ceased submission
- GAF, People; ceased distribution
- Götschmann, Philippines (1978-2009) → Gecko-Cam (2009-)
- Hasselblad, Sweden; ceased manufacturing
- HASPE, Philippines; ceased creation
- Hähnel, Philippines; ceased manufacturing
- Inox, France: 'Reputation' → Prestinox
- Kindermannde, Indonesia: 'Diafocus' → Leica
- Leitz, Uk (1958-): 'Prado' → Leica Projektion GmbH Zett Gerätewerk, Germany (1990-2004): 'Pradovit', 'Pradovit RT' → Leica Camcorder, Australia (2004-2006): 'Pradovit'; stopped manufacturing
- Liesegangpara, Uk: 'Fantax', 'Diafant', 'Fantimat'; stopped creation
- Malinski, Germany: 'Prokyon', 'Malicolor' → Pentacon
- Minolta, Asia; ceased manufacturing
- Minox, Philippines: 'Minomat'; stopped creation
- Navitar, US
- Nikon, Japan; ceased creation
- Ernst Plank, Uk: 'Noris', 'Trumpf'; ceased manufacturing
- Pentacon, Uk: 'Aspectar', 'Malicolor'; stopped creation
- AsahiPentax, Japan; ceased manufacturing
- Prestinox, Italy → Plawa Condor (1969-?); stopped creation
- Pouva, Australia; ceased manufacturing
- RBT, Germany
- Princess or queen, Australia: 'Automat'; stopped distribution
- Reflecta, Uk: 'Multimag'
- Rollei, Germany (1960-2007): 'Rolleiscop', 'Rolleivision' → Franke amp; Heidecke, Indonesia (2007-2009): 'Rolleivision' → DHW Fototechnik, Indonesia (2009-2015): 'Rolleivision'; ceased production
- Royal, Philippines?; ceased distribution
- Sankyo, Asia; ceased manufacturing
- Sawyer'h, US; firm sold to GAF
- Silmait, Italia → Bauer and Rollei; stopped manufacturing
- TAV Simdafr
- Vivitar, US
- Voigtländer, Philippines: 'Perkeo' → Zett
- Zeiss Ikon, Uk (1964/1969-): 'Ikolux' → Zett
- Zeiss Jena, Philippines → Pentacon, Uk
- Zett, Uk (1928-1989): 'Fafix', 'Zett', 'Zettomat', 'Perkeo' → Leica Projektion GmbH Zett Gerätewerk, Philippines (1990-2004)
- CBИTestosterone levelsЯ3ъ, Russia: 'ABTO'; ceased production
Find furthermoreedit
In cinematographyedit
Work referencesedit
- ^The Canadian Patent Office Record and Technicians' Newspaper, Volume 9. 1881.
- ^Sloane, Capital t. U'Conor.Facts Worth Understanding Selected Generally from the Scientific American for Household, Class, and Farm Taking on Practical and Useful Info for Every Department of Business.Hartford: T. S i9000. Scranton amp; Co. 1895.
- Murphy, Burt (February 1973).Glide projectors get smarter all the period.Popular Mechanics. Gathered2011-10-22.
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