🦫 Canon Extender Ef 1.4 X Ii Compatibility
The Canon Extender 1.4× II has worked very well with the 70~200/4L IS on every EOS body on which I have used it, including FF bodies (but I have not actually used the 6D, although there is no reason to doubt compatibility). If you want to keep costs down, look for the original version, which is optically identical, and can be found s/h. Extending the effective focal length of select Sony E-mount telephoto lenses, the FE 1.4x Teleconverter increases the lens's magnification by 1.4x for a narrower field of view. The dedicated design maintains full communication between the lens and E-mount mirrorless cameras, including auto-exposure metering, autofocus, and Optical SteadyShot 2epxB.