Hi Val,
Just so that you can see what I mean with "the tunnel" that I see...some examples. Forget about focusing and everything else, I did the pics freehand without worrying about exposure time and everything else. Only the tunnel matters now.
For sure you will agree this quick macro-lens was a waste, no matter you final objective. Next time I will follow this known advice: "try these wonderful things in the shop itself".
I went yesterday to the photo shop where they kindly agreed to exchange the item for something else. I tested the extension tubes but I decided finally to go for the cheap solution "magnification glass" because for the same cost (54 euro) I had paid for the "mistake #1" I have now two magnification glasses in diam 67 and 58, useful for my two objectives 17-85 and 70-300. I have greater hopes in the second, since this lens directly allows you to increase thigns much more but with a "con" of minimum distance of 1.2 m. I will see.
The extension tubes (I tested them) seem to be fine but for my objective EF-S they had no tube sold as single; If I wanted tubes valid for EF-S it was a set of three tubes, for "only" 199 euro. Perhaps in the future, but not one month after buying the 70-300 lens for "only" 550 euros. The magnification glasses were (tested in the shop, this time) giving approx a x1.5 magnification factor, and added to this you can reduce your minimum focusing distance to be 1/3 closer more or less, which is also a "magnification" in the praxis. In total things looked approx x2 bigger inmy first quick trial shots.
I will do some trails and post them later; I hope to be as systematic as you were Val! Your way of testing everything was "scientific" to sat the least! I will start to worry about depth-of-field, which seems to be the tricky thing in this kind of extreme close-ups.
If you are wondering about these high prices, it is so in Europe in general. I have seen in amazon.com same photo material roughly speaking 40% cheaper but they donīt deliver to my adress. Anyway buying something some hundreds expensive and sending it in small box all over the world is something I wouldnīt probably get used to.
Best regards