The problem is probably with the 50mm lens. Maybe you could just do the shoots without the services of the 50. How bad is the problem? And what exactly *is* the problem, E? I mean, what's going on? Are you sure it is a mechanical problem WITH THE EQUIPMENT, or is it perhaps some type of operator error with the exact,specific manner in which the equipment is being used? I'm not sure what the problem is....for example, if say it will not focus using the outer-most AF brackets, which are not cross-type AF brackets on most lower- and mid-level cameras, many times the camera will FAIL to achieve an AF lock on the desired target when the camera is held in either the horizontal or vertical orientation, BUT when the camera is rotated about 45 degrees either way, it WILL LOCK-ON!!!
So...what's the problem again???