I confirmed everything from the post I pasted. In summary when shooting close <10-15 feet and at low f stop's <4, results are adequate with limited vignetting. However even when shooting at infinity and an f stop of 22, you can get a usable print if you crop for an 8x10 or 11 x 14 image. This will get rid of the corner vignetting. These are the 2 sizes I most frequently print at. Given limitations, I wont use this lens often but may throw it in the bag for fun.
"Cameras and lenses are simply tools to place our unique vision on film. Concentrate on equipment and you'll take technically good photographs. Concentrate on seeing the light's magic colors and your images will stir the soul." Jack Dykinga