This is a Macro Coupler, also known as Reverse Ring. Use this ring to mount any lens reversely on your camera lens. These rings are frequently used to connect two lenses. More precisely, each male thread is mounted on the filter thread of a lens, and, consequently, these lenses are reversely mounted. Why are macro coupler needed? In general,when a lens is reversely mounted, magnification is increased. For example, if the prime lens has a focal length of xmm and the reversely mounted lens has a focal length of ymm, then the combined lens will have a magnification of x/y. Made of Metal.
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