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Message: <blockquote data-quote="Binastro" data-source="post: 3530864" data-attributes="member: 111403">Lee,It reminds me of the loudspeaker vibration parts that were used for active optics before anybody knew such optics existed.Maybe around 1970, but I wonder if earlier.Later such devices were available for amateurs but I don't know if currently made.Horace Dall made a variable prism extra for correcting atmospheric dispersion.Similar devices are available commercially.I am not sure if he patented any of his inventions.P.S.I don't think Dollond invented the Dollond achromatic objective. He was a better businessman.The Crayford focuser was I think left unpatented, maybe by Wall?Because something is patented, it doesn't mean they first thought of it.A friend became wealthy by patenting justifyably an oil industry valve that was available in a completely different context earlier.I think the world's first commercial autofocus camera from Minolta had problems, and they had to pay maybe Honeywell??Although Minolta's vibration sensor image stabilizer might be original. Used by others now.</blockquote>