I have a Canon Mark II Camera. I use all Canon L primes. In the past I had used a Sigma extender on this camera but it got stolen (it had worked great). I recently purchased a brand new Sigma extender (1x4) on Ebay from a reputable dealer. As soon as I got the extender I put it on my Canon 300mm F4 & tried it out. The auto focus still worked but nothing was sharp, also the camera wouldn't go lower than f6.3, then taking off the extender & just using the lens, still nothing was sharp. I realized something was wrong with the camera so sent it off to Canon Repair. Before sending off - I tried different settings. I use mainly aperture priority but even though I heard the lens focus, nothing was in focus. I only have the one camera so being without it has been awful. In hindsight, I think I should have sent the extender in with the camera for them to test it. I just sent off the camera & one lens.
Now I am freaked out about trying the extender on it again when the camera comes back. I've not heard back from Canon yet, my camera has been gone a week. Could it have been the Sigma that knocked out something in the camera or just a fluke thing happening? I now have one brand new sigma extender & am scared to think about trying it out again when the camera comes back! Any ideas, suggestions or thoughts would be appreciated. Any one else had any problems with the sigma?
