The response I give to everyone who wonders about camera and lens focus issues is this: Don't use a photo from a regular shoot to evaluate focus performance... there are simply far too many factors that can cause a poor result even when the gear is perfect.
If you want to know if your focus is working correctly, then test your focus using valid test conditions.
For example... if you allow the camera to auto-select the focus point, then it will always pick the AF point which was able to lock focus at the nearest distance from the camera -- and that may not be the point you had intended. You can force the camera to a specific focus point and make sure that AF point is hovering in front of the position in frame that you want in sharp focus.
When using "One Shot" AF mode, the camera only activates focus until it achieves focus lock. At that point the focus system shuts off. This means (and this is particularly critical in close-up photography) that if you are hand-holding the camera and you move... just barely... then you can (and probably will) completely throw your intended subject out of focus. This is because at close focusing distance the depth of field is very narrow (as you can see in your own photo). If your body were to lean forward or backward... perhaps by just 1/2 an inch... that would be enough to soften the focus.
There are a number of techniques to improve the stability of the camera while hand-holding it. This mostly relate to thinking about your body and camera in terms of your center of mass over your feet and bracing your body to support the camera to minimize the factors that cause camera movement. But nothing beats putting the camera on a solid non-moving mount -- like a tripod.
If you want to evaluate focus performance of the camera, you can use a focus target (you can buy a commercial target or you can download a target and print it yourself... my favorite downloadable/free chart is this one: http://regex.info/blog/photo-tech/focus-chart but I actually use a commercial chart for my own gear.) When testing... the camera MUST be on a tripod (no exceptions... if the camera is hand-held then the test results are not valid.) The chart must also be stationary (you can place it on a desk. My commercial chart actually mounts to another tripod.) Switch OFF the image stabilization when testing. Force the camera to use one specific AF point (if you want to test them all, you can, but don't let it auto-pick the AF point). Carefully align that focus point to the focus point on the test target. Take LOTS of test photos... it's always possible to have an anomoly. I manually run the lens out of focus between each test exposure to make sure that the camera has to run it back into focus. I actually manually run it out in both directions and keep track... e.g. run the focus out to infinity and make it focus back in and do that at least a half-dozen times. Then run the focus in to minimum distance so that it has to run the focus out to reach focus. This will help me detect if there's some gear backlash/slop such that the camera reaches focus accurately when focusing in one direction... but slop prevents it from reaching focus when running focus in the opposite direction. That would be an indication that the lens needs service.
In any case...using careful test conditions eliminates other factors from the equation... you don't have to worry that the subject moved... or you moved... or the camera wassn't steady... or the AF system picked a different focus point rather than your intended focus point, etc.
Tim Campbell
5D III, 5D IV, 60Da
