I don't imagine the lenses actually "move" - more likely they're a sealed pair of plastic lenses that change deformity when the pressure of the liquid between them changes and the screw is essentially a piston that controls that pressure. You just need a (hidden) bleed screw for filling and bleeding off any air. However, I'm not sure that a dyed liquid would be able to offer much variation in opacity using that method, and any effect would be more pronounced at the centre of the lens than around the edges.
Mac - MOULagain KI#00004826 00004289
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