I am playing with a loaned Mamiya 645 Super. Would someone please help me a little with things I cannot find in the manual? I have found the manual for the camera itself, but not for the grip or the finder. 1) What is the "START" position on the power grip for? 2) On AE prism finder, I see AV, Auto-AS, and SP position. What are these? 3) With standard 80mm N lens attached and looking into a view finder, and into a bright light, I see a faint diagonal line on right side of the view finder crossing the vertical portion of square right in the middle. Looks like an internal reflection to me. On left side I see the same thing but it is VERY faint - almost invisible. I cannot see it with 150mm lens. It also does not rotate when I partially un-mount the lens and rotate. Is anyone familiar with this?