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| focal length | |||
| optical lever (An experimental device used to measure angular rotation (e.g. in a galvanometer or torsion balance). Typically, a small mirror is attached to the rotating object, and a beam of light is directed onto the mirror and reflected onto a scale. The angle turned through by the beam is twice the angle turned through by the mirror. • Помимо оптиметра, принцип оптического рычага используется также и в оптических измерительных машинах.) | |||
