Opaque projector
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The opaque projector is a predecessor to the overhead projector. It displays opaque materials by shining the light down onto the surface from above. A mirror and imaging lens is used to focus an image of the material onto a viewing screen. Because they must project the reflected light, opaque projectors require brighter bulbs and larger lenses than overhead projectors. Care must be taken that the materials are not damaged by the heat generated by the light source. Opaque projectors are not as common as the modern "overhead".
In the early and mid 20th century, opaque projectors were produced as low cost toy projectors for children and were also marketed as an artist's enlargement tool to allow sketches or other images to be transferred to prepared canvas by tracing over the image, forming a guide for painting in oil or acrylic.
See also
- Projector for a directory of projector types