This is a phenomenon with digital SLRs. If the image sensor is fractionally out of alignment, even by microns, the point of focus will not fall exactly on the sensor. The first thing to do is get the focus ﬂange distance and AF sensitivity of your camera checked by the camera manufacturer. Getting this ﬂange distance corrected normally solves the problem however if the problem persists, we will need your camera and lens sent in so we can set the lens to your camera. If your camera is not reset first we may be setting your lens to a camera that is not to specification, which would mean your lens will not focus accurately with any other camera. Depending on the focal length and maximum aperture of the lens, the focus problem issues can be more apparent with some lenses than others.