The converter is used to attach "UCL-165AD Close-up Lens" on "28AD Mount Base DC35" / "28AD Mount Base MDFT2" / "28AD Mount Base MDFT1" / "28AD Mount Base DC40" / "28AD Port PT-027/020" for macro shot. (The converter is not necessary for other 28AD Mount Base.) *The AD Mount Converter for UCL-165AD is not necessary for a Mount Base except for "28AD Mount Base DC35" / "28AD Mount Base MCFT2" / "28AD Mount Base MCFT1" / "28AD Mount Base DC40" / "28AD Port PT-027/020" to attach the UCL-165AD *Vignetting at zoom / wide end. Zoom towards to telephoto side. Weight: 13.8g (0.5oz) [air] / approx.3g (0.1oz) [underwater]