1. This focusing helicoid tube is made with M52 front mount and standard M42 rear mount and light-weight alloy. It is useful for those lenses without focus ring, offers fine focus control for macro photography. 2. Mounting Extension Tube in between the camera body and l.ens will create more distance between the l.ens and film plane. By moving the l.ens further from the film or digital camera sensor, the lens is forced to focus much closer than normal. The greater the length of the extension tube, the closer the l.ens can focus. 3. Use this tube with your normal l.ens and you will get the quality, which is as good as the original l.ens and the size, sharpness and versatility is perfect for the macro and close-up pictures. Specification: Length: 17mm(min) to 31mm(max), it offers a total of 14mm movement distance for the l.ens focusing. Compatibility: M52 to 42mm screw mount lens and camera Colour: black Material: metal Package Contents: 1 x M52 to M42 (17-31mm) Focusing Helicoid Adapter Note: There is no electronic connection between the body and the lens Auto-focus function cannot operate. When using the extension ring with a DSLR/ SLR, the camera should be set in the 'M' mode Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.