Boy did my 5D3 run into its nemesis today for focus performance. I was trying to shoot my kids decorating the tree. They were not well lit, and the room behind was pretty bright.
My approach was to meter for the room in the background and then light the subjects with a bounced flash gelled to match the color temperature of the room in the background.
The problem? The 5D3 was almost incapable of focusing on the subject. No matter what I did with the focus point the 5D wanted to grab the background. I finally gave up and changed to the 1D4 which worked flawlessly.
Later I went back to the 5D3 and got another round of strange. I wanted to shoot two childen in silhouette with the tree lit behind them. I used the 5D3 with the 70-200. The camera was in one shot mode.
Even though the camera was in one shot mode, it wanted to act like it was in servo and I could not get it to stop. I would focus on a child which was a struggle again, it really really desperately wanted to focus on the better lit background. Then, even though I did not release the shutter button or do anything different the focus would jump back and forth to the tree. I've never had a Canon camera that would keep moving focus in one shot mode like that.
I don't know what to make of this so far, but the 5D3 certainly does seem to hate backlit scenarios. I will have to experiment some more.
