Hi Paul,
Welcome to the forum.
My experience of teleconverters is limited to the TC20 E converter. And I don't really like it, and as such very rarely use it. So crates in fact that I'm thinking of selling it.
The 1.4 and 1.7 may be better, but I've never used them.
The 2x converter does give good reach, but affects the aperture, so you need a fast lens to maintain a wide aperture when using the converter. I've never been that pleased with the results from my converter.
Have you considered something like the lens below? It may be the solution??
http://www.wexphotographic.com/buy-s...n-fit/p1025306
Hope this is of some help.