My copy is model A10 for Nikon mount, made in Japan.
There seemed to be a lot of variance in reviews for this lens. Some said it is sharp other said it produce poor image quality. For around a $100 for a FX/DX compatible lens, I decided to give it a gamble and try. Well it turns out both may be right.
My copy had a great deal of back focus. Assuming for a moment that many copies also have back focus, people who don't review the lens focus calibration and trying these on camera's without Auto Focus Micro Adjustment would interpret the image quality as very soft. My had to be adjusted to -15 on Nikon's scale of +20 to -20. After that the clarity was very sharp even wide open. On my Full Frame D600, Top sharpness seems to be right around f11-f16. Distortion starts coming into play around after f16, f20 still is not too bad and probably worth the extra DOF.
Optical Vignetting occurs below 22mm when the aperture is wide open, stopping down the lens a few stop resolves this.