51mm and 28mm were focused as close as possible. The camera was moved back until 75mm was the same size in the viewfinder as 51mm looked.

With flash
"100%" crops (Cropped, but not resized at all.)
300D Digital Rebel, sharpness 0, saturation 0, contrast 0
On a tripod, mirror lockup, remote release.
Several attempts at each aperture, chose the sharpest of the three (3 at 75mm, 2 at 51mm and 28mm)
Put in manual focus, then to infinity, then back to AF for each shot