Zenza Bronica Extension Tube Set C-A C-B C-C C-D For S2 EC

An extension tube, also called a close-up tube or an extension ring, is used with interchangeable lenses to increase magnification. This is most commonly used in macro photography.
The tube contains no optical elements; its sole purpose is to move the lens farther from the image plane. The further away the lens is, the closer the focus, the greater the magnification and the greater the loss of light (requiring a longer exposure time).