CowboyStudio One Way Macro Focusing Rail Slider Macro Bellows for Nikon EOS Cameras For use with Nikon mount type lenses Best for extreme Macro photography, with MAX magnify ratio up to 8:1 (3:1 with 50mm Lens) Bellows extend from 40mm to 150mm with locking thumb screw Built-in Tripod Socket for seamless sticking Allows smooth movement for more precise focus.