An alternative to the classroom instructor writing on a chalkboard (with his back to the students), the overhead projector was once a standard piece of audio-visual equipment. Consists of a base with a lamp and reflector directing the light through a table consisting of a micro-Fresnel lens, and an arm with the primary len(ses) and a 45° angle mirror.
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The lecturer would write directly on a scroll of clear film using special pens, or display a prepared transparency. Although still used and available, has largely been superseded by video projectors and laptop computers running presentation software such as PowerPoint or Keynote.
https://www.schooloutfitters.com/catalog/product_info/pfam_id/PFAM975/products_id/PRO721
The lecturer would write directly on a scroll of clear film using special pens, or display a prepared transparency. Although still used and available, has largely been superseded by video projectors and laptop computers running presentation software such as PowerPoint or Keynote.
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