Extension tubes for M39

Description:
On most lenses, the manufacturers provide a focusing mechanism that extends only a few millimetres, partly to keep down costs and partly to restrict the lens to extensions for which its optics are optimised. To provide additional extension, one or more extension tubes can be added between the camera and the lens, to make the lens focus at closer distances and therefore produce higher magnification.
Features:
This brand new Macro Extension Tube Set for your film & Digital SLR includes 3 extension tubes - 7mm, 14mm, 28mm adapters.
Use this set will not downgrade the optical quality of your lens. 
Sharpness and Saturation can be still maintained. But they are not meter-coupled. They do not preserve the automatic diaphragm. 
It should be used with manual lenses with their own aperture dial.
There is no electronic connection between the body and the lens. Automatic lenses can be used with their widest open aperture only.
When using the extension ring with a DSLR / SLR, the camera should be set in the 'M' mode