I found this to be interesting and somewhat puzzeling

grafxman · Sep 6, 2013

I received the SigMonster today. That's Sigma's 300-800mm, 13 pound nearly 2 feet long superzoom. I mounted it on my tripod, placed the 7D with Sigma's 1.4X TC on it. It auto focused flawlessly. I then placed Sigma's 2X TC on it and was astonished to to see the 7D still auto focused flawlessly! I expected to have to manually focus it with any teleconverters attached. I then tried it with the 6D. I was somewhat dismayed to discover the 6D would not autofocus at all with any of the teleconverters attached. I had planned on using it with the 7d anyway and I had expected to have to manual focus anytime I have a TC attached so it's all good. Still, it just seems a bit odd that the 7D will autofocus and the 6D won't when a TC is attached.

Derrel · Sep 6, 2013

Well, I'm POSITIVE that the 6D was not on the market when the 300-800 was designed and made. Perhaps the Sigmonster can both "recognize and say hello to," and also can "talk to", the 7D, which has been around since 2009. I dunno...it is a nice thing that it WILL AF with both TC when used with the 7D...I wonder if Sigma can update the CPU in the lens? Is the lens part of Sigma's very-newest rebranding/re-casting of their lens line, or is it an older lens that's from the pre-renovation days?

Dao · Sep 7, 2013

Just a side note, Sigma seems to be doing something I think is good for consumer. I found this Sigma USB Dock article the other day. Chances are firmware of the future release Sigma lenses could be updated with this hardware and the Sigma software. From dpreview: "It's a pretty simple concept - it allows you to plug a lens into a computer and update its firmware or tweak its operational settings using Sigma's 'Optimization Pro' software."

Overread · Sep 7, 2013

Yep Sigma's new USB design will be a major boon for their range - no more having to rechip!

As for the teleconverters, each Camera tends to talk a little differently so chances are the 7D just can't see the teleconverter, whilst the 6D can. Also note that both should be able to AF when in live-view because that has an upper limit of f8 (the sensor gets more light because there is no light lost going up into the mirror box for the viewfinder).

You can "tape the pins" on the teleconverter, this keeps the setup working but also blinds the camera to the teleconverter being present. If you google you should be able to find the right pin to tape over.

grafxman · Sep 7, 2013

Thanks folks. I was aware of the "tape the pins" trick. I used it on my 6D with the Canon 24-105mm in an effort to get a better zoom range with it. It worked with the 1.4 Kenko TC until I got down to the wide angle area at which time it would "crash the camera". Then I would have to zoom out a little bit and cycle the power switch.

A bit more info about my original posting. Yesterday I had it mounted on a tripod and used live view. I have no intention of using on a tripod however. I bought an old drive-in restaurant window tray off ebay for a lens rest. Today I backed the car out of the garage, mounted the tray on the window, covered it with a towel and started playing around. This way I can use the eyepiece or so I thought. It turns out that auto focus only works in live view! I guess I'll be packing more batteries.