noun
: an optical device that consists of a series of concentric opaque rings of such width that rays from alternate half-period elements are cut off and that has some properties of a converging lens
noun
: an optical device that consists of a series of concentric opaque rings of such width that rays from alternate half-period elements are cut off and that has some properties of a converging lens
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012