Wed 27-Jun-12 04:00 AM | edited Wed 27-Jun-12 04:02 AM by ShrimpBoy
When reviewing the image on the back of the camera, pressing the up or down button on the 4-way controller will cycle through different levels of data display, one of which shows the actual focus point that was used for focusing as a small red box. View NX can show you the focus point too if you want to do this on the computer.
If the image is not in sharpest focus at this red box, your camera's AF system possibly needs calibration or you need to turn on AF Fine Tune and set up an adjustment for this lens.
If the red box does match the sharpest focus in the image, then AF is working and you have to discover why that red box isn't where you wanted it. The most likely answer is that you're using the 39-point 3D tracking mode, which allows the camera to continually shift focus between the entire grid of AF points. On some subjects it will dance all over the place. Try a non-tracking mode where you have to tell the camera which AF point to use and see if that helps.