Have you ever looked at one of your images that was taken with a wide-open aperture setting and noticed that the focus is off? Maybe it appears to be behind where you thought you focused? This may be due to the lens system doing something called back-focusing. Usually it’s not extreme and only really noticeable when shooting wide-open but if you are doing any sort of macro work, it can be very frustrating. You can also have the opposite problem where the area of sharp focus is in front of the intended focus point, called front-focus. The easiest way to check this is to print a focus chart, put your camera on a tripod at a 45° angle, focus on the center point using the auto-focus, with the lens set wide open, take a photo, and then look at your image on your computer at 100%.
If the sharpest area isn’t right on the center line, then you probably have a back or front focus problem. If you have a mid to upper-level DSLR, you can probably fix that problem by adjusting the auto-focus system to compensate for the front or back focusing.
On the Nikon camera systems (D300 and up) you can go to the camera setup menu and look for the item called AF Fine Tune.
Turn the AF Fine Tune on and then go to Saved Value to enter the adjustment screen.
Now simply make an adjustment, save it, and then repeat the process of shooting the focus target again.
You may need to make several adjustments before you get the focus looking just right (see image below).
Now that you have that lens focus adjusted properly, check the focus on your other lenses because the adjustments are only saved for that particular lens. Cameras like the D700 can save focus data for up to 12 different lenses. Be sure to check your owners manual to see if your camera has this feature and how to use it.
If you would like to download the focus chart that I used, check out FocusTestChart.com and then download the pdf file and print it out. There are also commercial focus test charts available for purchase like the LensAlign from Michael Tapes (the guy that brought you the WhiBal and the Instant Raw from JPEG utility).
Canon shooters, check out this article over at Northlight Images for information of micro-focus adjustments on several camera models including the 1D MkIII, 1Ds MkIII, 5D MkII, 50D, and 7D.