Regarding using a 1.4TC on the Tamron. I played around with it some on my 6D, and took the tape off of the contacts of my Kenko 1.4TC to allow it to \"report\" to the body, as I was curious what it\'d say. Well....the Tamron must not have the contacts necessary to report anything related to TC\'s, as it still pretended the TC wasn\'t there. And I\'m still surprised how accurate it seems to be on my 6D.
Please look at the lens mount side of the Tamron lens and pay close attention to the golden contact pins. There would be two groups. One group would have 2 contacts and the other group could either have 5 or 8 contacts.
If there are only 5, then the TC will not pickup the info and therefore can not report the correct info to the body. If there are 8 contacts, like all the big whites, then the information gets relayed correctly. The 100-400L is in this configuration, while the wide Ls only have 5 pins.
Please take a picture of the lens mount and post if you have the time.
