Figure 6-2. Focusing
C. Lamps. The electric lamps that replaced the oil burners in classical lenses
must be large enough to replicate the flame of the burner. For that reason,
120 VAC 250 Watt, 500 Watt and 1000 Watt lamps are used (the 500 Watt
lamp is no longer in production). Use of 12-volt lamps, or 120-volt lamps
other than listed above, can lead to chromatic aberration (poor optical
coupling of the small light source to lens causes the light to broken down into
its wavelengths (colors)).
6-2
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