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NAO Volume II – Questions & Complete Answers
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NAO Volume II – Questions & Complete Answers
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NAO Volume II – Questions & Complete AnswersED Right Ans - Effective diameter. Twice the longest radius. Used to
determine the smallest lens blank that needs to be cut.
B Right Ans - The vertical box dimension or the vertical distance between
two horizontal tangents to the vertical extremities of the lens shape.
DBL Right Ans - Distance between lenses
DBC Right Ans - Distance between centers. See GC. Frame PD
GC Right Ans - The geometric center of the box, eyewire, or lens shape
OC Right Ans - Optical center. Point of not prism
Why did the FDA ban cellulose nitrate as a frame material? Right Ans - It
was too flammable to be considered safe
When were lenses first set in frames? Right Ans - Late in the 13th century
Who were the first spectacle makers? Right Ans - Goldsmiths
Which of the following frame materials was not used until the 20th century?
Right Ans - Stainless steal
Why is plastic a popular material for spectacle frames? Right Ans - It can
easily be molded and shaped.
What special care is required for nylon frames? Right Ans - Periodic
soaking in water overnight
What plastic frame material is the only one that can be either pantographed or
injection molded? Right Ans - Cellulose acetate
Which of the following plastics will shrink if over-heated? Right Ans -
Polymide
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