Just got a set of extension tubes. China made. Fully manual--no electrical contacts, not even for aperture. So to set a particular f-stop in Canon cams you first dial in the aperture and then while holding down the depth of field preview button remove the lens. That locks in the f-stop. After taking the lens off confirm that the aperture has in fact closed down by looking through the lens.
The set came with three tubes. For the shots below I mounted all three on the cam and used an EF 50mm f/1.8 II. Total extension length from body to lens is 2.5". No idea what the equivalent magnification would be. I chose an aperture to f/16 but even then the depth of field was frustratingly very shallow. And with the aperture closed down the view through the viewfinder was anything but bright. I was hand-holding the cam and focused by moving the camera forwards and back. Given that I had moving subjects I switched over to continuous shooting and sprayed away. Fortunately these couple of shots had decent sharpness.
I didn't use flash and relied on the fickle sun (yeah, it's actually the clouds' fault) for sufficient light. Both shots were taken at 1/100". I wanted to bump up the shutter speed but I was already at ISO 800 and noise was going to be a problem.
Shown below are the extension tubes and the adapter rings for the camera body (top left) and for the lens (top right).
The tubes and adapters all threaded together: