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MANAGERS AND PROJECTIONISTS 913
72 — How can you test projection lens for distortion? 148
73 — What is it you really do when you "focus" the picture ? . . 149 74 — Can you alter the E F of a projection lens by changing
length of barrel? 150
75 — Can the same projection lens be used to project different size pictures ? 150-154
76 — How would you calculate the size of picture a Jens will project at given distance if you knew the size it will
project at another distance ? 154
77 — How would you measure the focal length of a lens?. .150-153
78 — How would you measure the E F of a lens ? 152
79 — What effect has the E F of a lens on picture size at given
distances ? 154
80 — Are lenses made in the United States satisfactory? 156
81 — Under what conditions are anastigmat lenses of value?.. 156
82 — Are so-called "lens tables" of any value? 158
83 — Describe projector optical train in detail 160
84 — Can projector optical system be judged by ordinary
standards ? ' 160
85 — Name difficulties projection lens labor under 160
S'6 — Explain practical operation of law of light quoted page
161, and tell us how you would prove its correctness 161
87 — What is the first problem to be considered with relation
to projector optical train ? 163
88 — Of how many lenses may condenser be composed? 164
89 — What is effect of discolored condenser lenses ? 164
90— What is effect of "pitting" of collector lens? 165
91 — What is correct thickness of condenser lens edge? 165
92 — Name objections to too-thin and too-thick condenser
lens edge 165
93 — What importance is attached to accurate curvature and
polish of condenser lenses ? 167
94 — Explain, in detail, exactly what condenser does 172
95 — Name types of condenser used and give full diameter
of lenses and diameter free opening 168
96 — What difference is there whether convex or piano sides
of plano-convex lenses be together ? 168
97 — Under what conditions would you use meniscus bi-convex
combination ? 169
98 — What advantage has meniscus bi-convex over plano-convex under some conditions ? 169
99 — Under what conditions would you reduce diameter of
your condenser ? 169-170
100 — Name one serious objection to large diameter condenser. 170
101 — How close should condenser lenses be to each other? 170
102 — Why should condenser lenses not be in actual contact?.. 170 103 — Why should condenser lenses be not more than l/16th
apart ? 170
104 — Explain why spacing condenser lenses wastes light 171
105 — To what is condenser breakage usually due? 171-172