Manual Lens Adapter with Helicoid Macro Tube for M42 42mm Screw-Mount Lens to M39 39mm Screw-Mount Camera Body.
The macro function of this adapter provides a focusing helicoid that will increase the lens-to-sensor distance, allowing for closer focusing than normally allowed by the lens itself.
This means you can now get macro performance without needing to switch to a lens and you will retain all the normal benefits of your optic when the macro function is not in use.
It allow you to take close up/macro image more easier when full extended. It can focus infinity when closed of course.
The length of this Helicoid tube 17mm-31mm, (14mm movement distance for focusing)