While extension tubes don't have any optical ellements of their own, they magnify the flaws in the lens they're used with, and they diminish the light getting to the image sensor. Since your other lenses are pretty dim to start with, your 50/1.8 will probably be the most useful.
Kenko makes two types of extension tubes. One uses molded plastic release buttons just like on your Kenko TC. These are good. Kenko also makes another, cheaper kind that use a formed sheet metal lens release. These aren't so good. I've seen reports of them getting stuck and of light leaks.
- The lens is the thing.
- 'Full Frame' is the new 'Medium Format'.
- "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.