I have a Kowa Graphic (Computar) 240mm lens on trial, It is in barrel mount. I have mounted it on a lensboard where the rear element penetrates the lensboard and is flush with the rear of the lensboard. A Packard shutter is mounted flush up to the rear, so it basically touches the metal rim of the rear of the lens. I am getting vignetting on 11x14 focused at infinity at f64. I was wondering if this lens only covers 11x14 when mounted in a shutter? Any advice? It IS supposed to cover 11x14 isn't it?