I was photographing an outdoor concert thursday night, with the 60-250 mounted on a tripod. I was using live view and back button autofocus, then fine tuning the focus with manual focus
Everything was fine... until at some point, it wasn't. It was really weird. autofocus seemed to have stopped working (the switch hadn't been flipped on the lens or the body), and manual focus worked just long enough to make the image even worse, and then didn't do anything anymore. I triple checked everything... no dice. I couldn't even see anything happening inside the lens when I focused, but it was dark, so I may have missed it. (Zoom still worked fine)
I THINK this happened just after I'd temporarily removed the lens to switch to a wider angle (F 28-70/4), hand held, and then went back to it.
After this, I took the camera off again, put the other lens on so I could at least get some photos of the set. After the band finished and the next group started setting up, I took the lens off the tripod and got a better look inside and it looked like things were moving when I turned the ring. I decided to give it another try and put it back on the camera.. and it worked perfectly fine.
The only thing I can think of is that maybe because I had the collar loose, maybe when I mounted it back on the first time after switching, I didn't screw it all the way in to place and something was misaligned, like the lens was focusing slightly forward of the sensor, and maybe the SDM contacts weren't both touching so I couldn't AF.
Does anyone have any other ideas? I don't want to have it fail on me again, it's too pretty and too expensive to screw up.
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