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 Thanks for the pointers. I found that lens turrets are most commonly found in the context of microscopes, and there's no mention in the Optical microscope article. One also finds a similar mechanism in machining, to swap tool bits such as drills. I haven't yet found a mention of this usage in the Metalworking articles. including CNC.  

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 I don't think the images "Turrets at Donaldson's College, Edinburgh, Scotland" or "Turret atop Havant dental surgery" should be provided as examples because, per the article, these would be considered towers not turrets because they extend to the ground.