I am positively surprised by the extension tubes for the very reasonable price. They do what they want and that the minimum focus distance shortened by a smaller magnification to achieve. The AF transmission does not interest me because I always just manually working in the macro range, but the importance of the diaphragm mechanism and it works flawlessly in all variations. They are more stable than expected. To use all 3 extension tubes to use as close as possible to take pictures but it needs a lens with a long focal length to the 200 to 300mm. With my max. 70mm (0.38 cm minimum focusing distance) at the Eos 6D I come with the 21mm intermediate ring at a working distance of about 1 cm (at max Closest focusing distance on the lens) to a maximum magnification ratio of almost 1: 1. When I mount a second intermediate ring, with said 70mm lens on the on the max. Closest focusing distance is provided by 0.38cm, the focal plane is "in" objective and no longer before the lens as it should be. The only solution is longer focal length. For me 5 stars, class parts.
