After I figured out how to un-attach the ring from the lens, I tried it. Of course the extension rings really reduce light input. I needed my speedlight to illuminate the subjects. It was also very hard to see well enough to focus. But on some elementary easy subjects I got some interesting results. Here three rings (about 1 3/8 inches of extension) were used.
The fingernail of a painter
Fingerprint
Dead Leaf
The Spent Stamen
Another Stamen