150-600 Sport with Canon 1.4x MkIII Converter.
About a year ago, after I bought my lens I posted on here that I couldn't get the lens in focus when mounted on my Canon 7DII with my Canon MkIII converter, even at maximum micro-adjustment on both the body and the lens. I even went so far as to buy the recommended Sigma 1.4 TC1401 converter, but I found on the first day that it was just as bad, but slower then he Canon, so back it went. The lens focused fine with live view.
When Sigma brought out a firmware update for the lens, supposedly to improve autofocus, I hoped that would cure my problem. In fact it did the opposite. The camera would no longer communicate with the lens when the 1.4x was mounted, not even in live view, when a screen popped up telling me to ensure that a lens was connected.
I gave it up as a bad job until recently. My camera dropped onto my foot from about knee height at Easter and although everything seemed OK at first I found that under certain conditions white objects appeared to bleed into adjacent black areas to the right of them. I sent the lens to Sigma in the third week of April and mentioned the focus problem with the 1.4x at the same time.
Sigma UK told me that they had detected a bit of rear-focusing on the lens and had corrected that and they replaced the mount (I assumed this would correct the focus problem), but they could find nothing wrong with the optics. It went to Japan for them to check it in the 2nd week of May and eventually it arrived back from them on 1st July with the message from Japan that the lens was fine and was within manufacturing limits. Quite why it took them 6 weeks to find this out I don't know. I had assumed the delay was down to getting parts. But OK, at least the lens wasn't damaged.
Anyway. I tested the lens and found straight away that the problem with the tele-converter was no different than before. I got back in touch with Sigma UK on Monday and today after a second email to them I received this reply;
I am sorry for the delay in getting back to you. I did know the answer to your problem and had to e-mail Japan. Normally in these cases I would let the customer Know what was happening but unfortunately on this occasion it slipped my mind.
I have heard back from Japan over the issue where the lens is not recognised by the camera when using the Canon tele-converter.
What you have experienced could unfortunately be down to the content of the latest firmware update of the lens which was designed to improve its AF performance. I must mention that Sigma do not guarantee the functionality of our lens when using other manufacturers converters. That withstanding if it was working on your camera with the Canon converter before you updated the lens firmware then if you send us the lens we can install the earlier version.
That was what I suspected all along. The firmware update screwed things up. I've since found from googling that other users experienced exactly the same problem.
http://photography-on-the.net/forum/showthread.php?t=1439030
What gets my goat about this is the fact that Sigma designs lenses to fit different manufacturers' equipment and bases its whole lens business on this, relying on us users to take advantage of it. They then appear to have designed a firmware update than actually excludes a piece of Canon equipment. Their bread and butter, and when it's brought to their attention they claim that it's nothing to do with them; 'I must mention that Sigma do not guarantee the functionality of our lens when using other manufacturers converters.'
That is bizarre!
I know they want us to buy the dedicated TC1401 (which only fits about three of their lenses), but that is surely taking the Mickey.
Incidentally. I mounted the lens and converter on my old 7D MkI as a test and lo and behold the camera picks up the lens and autofocuses in live view.
Black mark to Sigma.
I don't think I'll be taking up their offer of earlier firmware. It would be daft to lose any improvements in autofocus just so that once in a blue moon I could fit a TC