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912 HANDBOOK OF PROJECTION FOR
46 — What limits the maximum diameter of a projection lens
of given E. F.? 139
47 — What data is it necessary to send when ordering a new
proj ection lens ? 139
48 — What range of focal lengths of projection lenses are
carried in stock ? 140
49 — What is it necessary to do when you wish to order a
projection lens to match one you already have? 140
50 — Can markings of projection lenses be depended upon for
accuracy ? 140
51 — What effect, other than light loss, has an accumulation
of dirt on surface of lenses ? 146
52 — Name two faults for which projection lenses must be
corrected ? How is it done ? 132
53 — How is lens diameter affected by revolving shutter ? . . . . 208 54 — Do you thoroughly understand the lenses you are
using?
Practical Projection Optics
Under this heading will be found many things duplicated in other sections. This is necessary, because, as a matter of fact, practical projection optics really includes about everything.
55 — What is brilliancy of arc crater per unit area? 392
56 — Upon what does total light giving power of crater
depend? 392
57 — What effect has distance of light source from collector
lens on light delivered to the spot ? 162
58 — What is "working distance" of projection lens? 152
59 — What is "Equivalent Focus" ? 152
60 — Describe universal system of lens measurement 153
61 — Why should lenses be kept perfectly clean? 137-141
62 — Name some satisfactory solution for cleaning lens 137
63 — Name cheap liquid which will remove oil from lenses
and clean them very well 139
64 — What kind of cloth or skin should be used to polish
lenses ? 137
65 — How often should interior surfaces of projection lenses
be cleaned ? 138
66 — How often should you examine and clean exterior surfaces of projection lenses ? 137
67 — What will be the result of wrongly re-assembling
elements of projector lens ? 138
68 — What is guiding rule for re-assembling ? 138
69 — What happens if interior of projection lens barrel is not
kept black? 138
70 — Why is diameter of projection lens of great importance?
147-148 and 186 to 190 71 — Is it desirable to have projection lens diameter greater
than is necessary to receive the entire beam? 148