Description 1. This focusing helicoid tube is made with standard M42 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 lens will create more distance between the lens and film plane. By moving the lens further away 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 lens can focus. 3.Use this tube with your normal lens and you will get the quality, which is as good as the original lens and the size, sharpness and versatility is perfect for the macro and close-up pictures. 4. 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 Specification: Material: Coated Metal Length: 25mm(min) to 55mm(max), it offers a total of 30mm movement distance for the lens focusing. Compatibility: M39 to 42mm screw mount lens and camera Note: This adapter consists of one piece M42-M42 extension Tube and one piece 42-39mm Step Down Ring.