I would like to buy the Kenko extension tubes (set of 3) and the Kenko teleconverter 1.4x but have read conflicting reports over the compatibility of the extension tubes with EF-S lenses and the teleconverter with the EF 70-300mm IS lens. The only EF-S lens I use is the recently purchased 15-85mm and I probably wouldn't be using the tubes on it anyway, but would love to get a bit more reach on the 70-300mm lens with the teleconverter. Is it right that the Canon teleconverter will only work on an L lens?