I need a couple of other questions answered about the 300 F4.5 Series II Velosti gmat VF. The part of the lens in front of the shutter, that is, all of the lens in front of the shutter can be rotated and is this normal or something that nee ds to be fixed/addressed? In other words, the front of the lens, and the lens itself can be rotated even though I accidently did this once and only once,for fear this is not as it should be. Being new to LF, I have no idea if this is nor mal or not. Incidently HOW DO I GET THIS LENS TO OPEN AND CLOSE? I don't see a lever or button for opening or closing the lens.