The 165mm LS is one of the finest and does not need a finger pointed at it; problems come up are in the "small detail" relating to correct use of either this LS lens or its smaller 90mm cousin. In leaf shutter mode the camera-side shutter speed must be set to 1/8 or only part of the frame will be exposed. A higher sync speed can also dramatically raise the risk of damage to the LS mechanism and the camera shutter. It really is important to get on top of it as a priority.