Bloomed lens

Coating a lens with a layer of magnesium fluoride (n =1.32) one quarter wavelength thick, suppresses reflection since, waves returned from the upper and lower surfaces are one half wavelength out of phase. Zero reflection occurs for only one visible wavelength.

Compound camera lenses reflect in many colors, depending on the exact thickness to the MgF2 layers. A coated lens is said to be 'bloomed' because the appearance of the surface in reflected light is similar to the bloom on ripe fruit (plums, grapes, etc) due to an oil layer on the skin.

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