Finder
Veteran
I would hate to point this out, but vignetting is greater wide open as the hood would have a greater affect on reducing the size of the pupil. Stopping down makes the pupil smaller which can eliminate the vignetting completely.
How sharp the vignetting is has more to do with the placement of the vignetting aperture (and focal length) than the aperture in use - especially since small apertures are unlikely to be vignetted. The sharpness of the vignetting aperture dedends on its relative distance between the effective aperture stop and field stop in the optical system. The closer it gets to an effective field stop, the sharper it is.
How sharp the vignetting is has more to do with the placement of the vignetting aperture (and focal length) than the aperture in use - especially since small apertures are unlikely to be vignetted. The sharpness of the vignetting aperture dedends on its relative distance between the effective aperture stop and field stop in the optical system. The closer it gets to an effective field stop, the sharper it is.