I'm hoping for the opportunity to try some star photography (Not star trails) with my A7r over the next week weather permitting, and was wondering if anyone has had experience trying this with the Zeiss 16-35 f4? I understand that f4 may not be so great for this. Any tips on where to limit my ISO or shutter speed for focal lengths between 16 - 24mm would be appreciated. I do also have a Canon FD 20mm f2.8 & 24mm f2.8 which may not be as sharp as the Zeiss, though happy to try whatever lenses I have at hand. Cheers!