Originally Posted by
Michael S. Briggs
The aperture won't be defined entirely by the iris blades, but also by for some portion of the shape by the barrel. It sounds like this is happening with your Fuji-T at f22 at 110 mm radius. If the area of the ellipse that is cutoff is small, probably Fuji considered it acceptable reduction of illumination in the effected corner. What fraction of the ellipse is cutoff at f22 at radius 110 mm? Avoiding this would have required larger glass elements and a much heavier lens. Because of the cutoff, you are losing some illumination to the corner beyond the simple mathematical model for an ideal lens.
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