[cyclohexane]

Not hard to believe. You probably don't want to be using a teleconverter with a lens with a variable max aperture of f/4.5-5.6. The TC-14E, even, will take you to f/8, which is pushing the limits of autofocus even more (f/5.6 already is, to some extent). Also, due to the degredation inherent with the use of TC's, you won't be doing anything to help optimize your image quality. The fast telephotos have the use of TC's factored into the design phase, and therefore can take the teleconverters with minimal degredation, but even then, you're still reducing the quality of your final image.