This test addresses the question of minimum and maximum focusing distance with a 12mm Kenko Extension tube and a 50mm f1.8 MkII lens. With the Rebel on a tripod and the camera in AV mode, f8, the test subject was set on the counter. The lens was placed in manual focus mode. The lens was manually focused at both extremes. The closest I could focus was 5.5 inches from the test target and the furthest I could focus was 9 inches. This was measured from the test target to the center of the front element of the lens.