I have a sigma 70-200 f/2.8 HSM II and its well know that the Sigma 1.4XTC is not compatible with the pentax mounted siggy.I really want to use a TC with this lenses so I do have others,namely
Tamron-F 1.4X Pz AF MC4 98-280mm range has HSM contacts
Pentax F 1.7X 119-340mm range doesnt have HSM contacts
Kenko Pz AF 1.5C Teleplus SHQ 105-300mm range has HSM contacts

which has better IQ


cheers