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Overhead  projector
Portable overhead projector - 14229_335

Religious Program Specialist 3 & 2, Module 01-Personnel Support
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perfect   focus   of   the   light   rays   which   pass through the lens. Directly above the Fresnel lens is the 10-inch by 10-inch projection stage where the projectuals are placed. The objective (projection) lens  is  supported  centrally  over  the  stage,  This lens focuses the image of what is to be projected onto  a  45°  front-surface  mirror,  which  in  turn reflects the image to the screen. Attachments may be provided that will allow the  overhead  projector  to  be  converted  into  a device  that  will  project  35-mm  slides,  35-mm strip   film,   or   lantern   slides.   Additionally,   a polarized  disk  may  be  attached  to  the  projector allowing specially prepared animation projectuals   to   be   shown   which   will   give   the audience the effect of movement. Portable Overhead Projector The  portable  overhead  projector  is  a  self- contained unit.  (See figure 7-6.)  Due to the 142.339.1 Figure 7-6.—Portable overhead projector. unit’s portability, the space between the projection stage  and  projection  head  is  limited.  As  a  result, the    use    of    this    projector    with    overlay-type projectuals is limited. A  unique  feature  of  this  device  is  that  the blower  motor  is  thermostatically  controlled.  The thermostat  maintains  a  constant  temperature  in the vicinity of the lamp which prolongs the lamp’s life.  When  the  two-position  switch  is  turned  ON, power  is  applied  to  both  the  projection  lamp  and the blower motor. When the air passing around the projection lamp is heated to 130°F, a thermostatic switch   closes,   providing   a   secondary   path   for electrical  power  to  the  blower  motor.  When  the projector  switch  is  turned  OFF  the  blower  motor will   continue   to   operate   until   the   thermostatic switch  opens.  The  thermostatic  switch  will  open when  the  temperature  of  the  air  passing  around the  projection  lamp  falls  below  130°F,  For  this reason  power  should  not  be  removed  from  the device     until     the     blower     motor     shuts     off automatically. The overhead projector, shown in figure 7-7, is another type of portable self-contained unit. Overlay-type   projectuals   that   do   not   extend beyond  the  top  of  the  viewing  stage  can  be  used with this projector. This device uses a quartz iodine lamp instead of the   standard   projection   lamp.   The   transparent envelope  is  made  from  quartz  (in-stead  of  glass). Quartz  resists  heat  and  permits  use  of  higher wattage. Caution must be observed when handling the   quartz   lamp.   Stains   from   fingerprints   can cause lamp failure. When lamp failure occurs, the lamp may explode when lighted. For this reason a safety switch cuts off the current to the lamp when the projector top is open. Opaque Projector The    basic    difference    between    the    opaque projector  and  the  overhead  type  is  that  light  is reflected from the surface of opaque objects rather than   passing   through   them.   (See   figure   7-8.) Examples     of     opaque     objects     that     can     be 7-18







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