I have had some troubles with it myself lately. I will take a string of pictures of my girls---and it almost never fails...the image with my favorite expression is the soft image. The images before and after it are strong and focused....then that "perfect" image between them is soft. It KILLS me!
A couple of weeks ago I visited Pictureline and talked to Ken (my go to camera question friend).
I have heard complaints in general about the Canon 5d and their focusing issues (both the 5d and the MarkII). I wanted Ken's opinion. A few things I learned:
Canon did improve their focusing with the 7d...and they might possibly extend those improvements into the 5d MarkIII (not yet released). Canon does also have a much better system in the 1ds. Nikon has more focal points...and they do have a more polished auto focus system. I am going to wait it out for the MarkIII---then I will decide.
Some of Ken's suggestions in the meantime:
- check my AF settings (ie: AI Servo, One Shot, AI focus) maybe it's time to quit being lazy in AI focus and actually select my setting for still (one shot) or moving (ai servo) subjects. One more thing to think about :)
- shoot in continuous drive mode and shoot A LOT OF IMAGES- I used to do this. A LOT. I went away from it because I wanted to get the shot right once and then move on. One thing I do notice---there can be the most subtle changes and expression...and it can make all of the difference. If I am continuously shooting---I will have more to choose from.
- adjust my diopter---I have to say I had never done this. I think this would be more important if you are manually focusing. He suggested focusing (auto) on an object (I think a flat plane would help so that you are clear on what is being focused on). Once you have the focal green light (it is green on my camera) then adjust the diopter wheel until the object looks it's sharpest. Easy! There is more here on this. Again...this is more important with manual focus.