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LENSES AND MIRRORS 95
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65. What is the safest method of matching a lens?
66. What information should be transmitted to the manufacturer in ordering a lens to match, another ?
— 67. Descrihe the marking used by one lens manufacturer.
68. How are matched lenses marked ?
Light Loss Through Reflection, page 117
69. What, according to optical -engineers, is the reflection light loss per surface ? S% %
70. To what else is light loss due?
71. Is light loss the only evil effect of dirty lenses ? ^Tt-ej ^
Cleaning Lenses, page 118
72. Does a very small amount of oil injure results ?
73. Do even the faintest finger marks do harm ?
74. How may faint finger marks be made visibk
75. What is best for cleaning lenses?
76. How often should lenses be examined?
77. When should mirrors be cleaned?
78. Should projection lenses be disassembled occasionally, the interior surfaces of the lens elements cleaned and the lenscoating examined?
79. Why is the projection lens barrel painted black inside?
80. What should be done if the black interior coating wears off?
81. What should all projector lenses makers do? ~sl+>
82. What marks should be affixed to projection lens elements by projectionists? ->i^.\<
83. What should projectionists be very cautious about in disassembling and reassembling projection lenses?
84. Just how tightly should the mount be screwed up when assembling lenses? ^/
Loss Through Absorption, page 119
85. How much light is absorbed in passing through crown or flint glass?
86. What is the loss in poorer grades of glass? /CJy/fct