This is the JJC Reverse Adaptor Macro Couplers 77mm to 77mm [JU7777R] This series of products are designed to allow the photographer to mount an additional lens face to face on the camera"s lens, via male-to-male reverse adapter,enabling high quality macro (close-up) images with high resolution and sharpness. It will work by reversing a standard lens to the front of a telephoto lens. ...Contact us if you need more help.