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(With reference to a lens or other optical system) the focal point or focal distance for actinic light.
Mid 19th century; earliest use found in Art-union.
雅致网英汉双解词典包含236457条英汉翻译词条，涵盖了常用英语单词及词组短语的翻译及用法，是英语学习的必备工具。