135 is a nice lens and goes well with extension tubes, but no lens can compare to a dedicated macro lens for image quality in macro shots because extension tubes always have negative effects on IQ - anywhere away from the center of the image loses quality fast, some faster than others. 85L and 50L lose quality away from center extremely fast, 35L fairly fast, 135L and 70-200 f/2.8L IS do well with tubes but still suffer towards the edges.
