Canon EF25 II Extension Ring
The EF25 II extension ring comes between the camera mount and any lens with an EF or EF-S mount.
It allows to reduce the lens minimum object distance to focus on object at very close range.
It doesn’t contain any optical element that could altered the image, the lens maintain its total optical quality.
The overall lens control and information it delivers to the camera are preserved by maintaining all the electrical contacts on the mount.
Extending the flange back by 25mm, it won’t allow to focus at long distance. It also induced a two stop loss.
If the minimum object distance are to small and the object is to far to be focused on, it’s possible to use the EF12 extension ring.