My XF400 camcorder can not focus when lens is wide open (f2.8 - 4). The problem is noticeable only as you zoom past 10X (zoomed wide the problem is not noticeable at all). If I close the iris to f8 or more, the camera can focus fine. This happens with manual and auto focus. During this, the camera will not show PEAKING. Auto focus will lock into a soft and out of focus image. Lens looks to my naked eyes clean of fungi and dirt.
Any ideas of what can be wrong or how can I fix it?