Complex sentence: However, it has also been widely reported to exhibit problems not present in the older 28-70mm f/2.8L--poor sharpness at its maximum aperture, and autofocusing "behind" the focus area selected in the camera.
Split into simpler sentences: However, it has also been widely reported to exhibit problems not present in the older 28-70mm f/2.8L. There are also many reports of the lens autofocusing "behind" the focus area selected in the camera.