This tube useful for lens without focusing ring. And it can be use as macro extension tube. There is no electronic element in the adapter, aperture and focusing must be manually control.

Specifications:Front mount:  M42 screw mount female (M42 x 1mm)Rear mount: M39 screw mount male (M39 x 1mm)Length: 10mm to 15.5mm (5mm movement distance for focusing)Focus: manuallyMaterial:  aluminium alloyPackage included:1 x focusing helicoidBrand new and unused