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Message: <blockquote data-quote="elkcub" data-source="post: 1651245" data-attributes="member: 14473">Actually, Henry, it's a clever idea.  I have no trouble clearly seeing four images using two toothpicks taped to the backs of overlapping business cards, and held at arms length.  The object distance for visual focus determines how far apart the toothpicks have to be separated for the middle images to merge.  It wouldn't be difficult to make a real instrument by adding calibration marks to the cards, or using a caliper like Ron. :t:Ed</blockquote>