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The Audio-Visual Handbook
There have been many improvements making these classroom lanterns adaptable to various situations.
These improvements include stronger illumination, lens equipment
Photo Courtesy Bausch & Lomb
A Standard Glass Slide Projector
of higher quality, adjustable bases for use when standing the lantern on an irregular surface, and readily accessible optical parts. It was formerly necessary to almost dismantle a lantern to change a lamp or clean the reflector and lenses. The modern lanterns are arranged with hinged lamp houses, so the entire optical system may be opened for inspection or for necesary care and adjustment by simply tilting the lamp house forward or backward. It was also necessary to exercise great care in replacing the lamp to be certain that the lamp was in perfect alignment with the optical system. The new projectors use pre-focused lamps, which may be changed by anyone, usually without making any adjustments whatever.
The average glass-slide lantern, complete with carrying case, costs approximately $70. This includes the lamp which is in the projector, and it is usually advisable to secure an extra lamp at the time of purchase to be protected from embarrassment or delay when the original lamp burns out. These lamps will give 100 hours or more of projection service on the proper type of current, but an unusual jar or careless handling of the projector may cause a lamp to break or burn out at any time.