I have a 4x5 camera with 135mm f/4.5 Tessar type lens. The image circle should b e very limited for movements yet when I give about 1 inch of frount rise, I don' t see any vignetting on the ground glass. This is when viewing the image at f/4. 5 (wide open). Why doesn't the ground glass show the vignetting? Certainly there should be some since I am rising the frount more than 6mm. How does one explain this?