Optical compensation foil

Over the next three hundred years, optical telescopes underwent vast technological improvements. For example, achromatic lenses were invented to compensate for the errors in color caused by older lenses that foiled to treat all the colors of visible light in the same way. Radio telescopes were first developed in the twentieth century, based on the discovery that faraway celestial bodies were constantly emitting faint amounts of radiation in the form of radio waves. This new form of telescopy was soon applied to both military radar operations and astronomical research. 

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