Source of polarised light for overhead projector - uses two confocal lenses and small light source emitting polarised beam and number of slides fixed at Brewster angle to deflect beam which is returned by mirror

摘要

The light source includes two confocal lenses (11, 12) to define an optical axis and a light source (10) of small size arranged more or less at the focal point of the lenses. A polarising assembly (14, 15), consisting of a reflector and rotator, is arranged to one side of the lenses to reflect the light beam on to them. A number of slides (13) with parallel faces are arranged on the other side of the lenses. These are inclined at the Brewster angle to the optical axis. A mirror (16) returns the beam deflected by these slides. ADVANTAGE - Provides image contrast which is the same for translucent objects and liquid crystal tablets.