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This is called a 'Fresnel lens' or 'zone plate lens', and it focuses light using diffraction rather than refraction.

Before the 11 a.m. boat ride back to the mainland, Dre Elmore likes to show off the retired Fresnel lens and the array of still-working machinery in the fog signal building.

The glint in Gallichotte’s eyes reflects the setting sun as he becomes more animated in the telling of their 2018 mailbox creation story: the purchase of reference books, hours of careful research, the need for authenticity, the acquisition of a Fresnel lens.

The first such lenses were invented by the French scientist Augustin-Jean Fresnel in 1819 to provide lightweight lenses for lighthouses.

Notable for the eponymous 1898 lighthouse — the tallest in Washington state — visitors can climb the 135 steps to the lantern room, where the original Fresnel lens still signals the Gray’s Harbor entrance.