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MANAGERS AND PROJECTIONISTS 911
17 — For practical purposes what may we assume the amount of refraction rays will receive in passing through a lens will depend ? 129
Lenses
18 — Explain the difference between a piano convex, a meniscus and a bi-cpnvex lens 168-169
19 — What is the principal axis of a lens ? 126
20 — What is meant by working distance ? 129-152
21 — What is meant by conjugate foci ? 126
22 — What do you understand equivalent focus to mean?. .129-152
23 — What is spherical aberration ? 129
24 — What is chromatic aberration ? 130
25 — What does focal length mean as applied to a simple
lens? 134
26 — Explain, roughly, the action of light through a lens.... 131
27 — What is meant by correcting a lens? 134
2&' — Explain how an image is formed 133-134
29 — How is curvature of simple lenses determined? 134-135
30 — Is it possible to focus an object having area to a
point? 133-135-136
31 — Why is it impossible to focus the condenser beam to a
point? .133-135-136
32 — What relation has revolving shutter to lens diameter ? . . 208
Lenses — Projection Lens
33 — What is a projection lens ? 38
34 — What is the function of a projection lens? What does
it do? : 126
35 — Of what elements does a projection lens consist? 136
36 — What is meant by the "front factor" and "back factor"
of a projection lens ? 136
37 — Which lenses of a projection lenses are cemented together, and with what are they cemented ? 136
38 — What is the optical effect of cementing the lenses of the
front factor together ? 144
39 — Are the lenses of the back factor always separated by
snacing rings ? 136
40 — What occasionally happens, or what may happen to the
cement (balsam) between the front factor lenses? 137
41 — Should or should not the lenses of projection lens be
clamped tightly in their individual mounts? 138
42 — How should Gundl^rh-Manhattan lenses be re-assembled ? 139 43 — Is it possible to repair a projection lens if one of its
lenses be broken ? 139
44— Should broken lens referred to in question 43 be sent to
manufacturer ? 139
45— Have odd lenses, or combinations of lenses, any value?. . 139