The common wisdom is that teleconverters will decrease image quality proportional to the degree of magnification offered by the TC. In fact, this is often extended to say that any added glass, including filters, must necessarily degrade image quality to some extent. The logic is sound, as the more fiddling with the light one does by sending it thru glass elements, the lower quality result one might achieve.
Although one does not expect a teleconverter to improve base features of the lens (sharpness, contrast, etc), it is not necessarily true that their addition will degrade performance. Such is the case with this combination. I find sharpness and image quality with the TC attached to be indistinguishable with the "bare lens." Check out these images.
Over the past few weeks, my lovely wife and I have been working hard to remove brush and dead trees from the landscape behind our house. I always take my camera with me everywhere, even into the woods while carrying a chainsaw in the other hand, and this day was no exception. All three of these images are among the fruits of that labor.
Top frame, we see some kind of lichen with "golf tees" sticking out of them. After I took a breather and plopped down on the leafed forest floor, I started rooting around in the leaf litter like I often do because I'm actually only 6 years old. This time, we found wide patches of this lichen with "golf tees" sticking out of them, and I took several shots.
Middle frame shows a glorious patch of turkey tail fungus growing on a moss covered log. We were moving logs all day (well, for a couple hours at least), but I refused to touch this one because it was just so fantastic!
Finally, bottom frame shows one of the few trees with leaves still on at the time, and berries too. This is a dogwood which is among our favorite trees. We removed some fast growing gum trees, a few gnarly cedars that were in the way, but we did our best to leave all the oaks and damaged zero dogwoods during our brush removing rampage.
Again, click any photo to see larger versions, and comments can be left on this page or under each photo if you are so inclined.