I tried taking a picture of a building using a substantial amount of front-rise and I got very serious light-fall off (not beyond the image circle because I can still see very dark features in the ground glass all the way to edge). Which H eliopan CF (3x or 8x) should I use with the Grandagon 90/6.8. I know Ellis uses and recommends a 3x for the 90/4.5 which if I recall correctly from I read in t he Rodenstock brochure has some tricks in it to minimize light fall-off. By eye , the difference between the center and outer regions is definitely more than 1. 5 stops at f6.8, but I'm worried that 3 stops from the 8x CF might be excessive. Does the light fall-off or difference between center and edges increase or dec rease as the aperture is closed down to f22? Does anyone have experience on put ting a Heliopan 8x CF on the Grandagon 90/6.8? I won't consider getting a "prop er" 2x more expensive Rodenstock CF unless someone convinces me that both 3x and 8x Heliopan CF definitely won't work.