For a lens of this angle, very low. At open aperture and stopped down sharpness and brilliance are very good up to the corners. Straight mechanism of front lens group, internal focusing, built-in lenshood. Outstanding when stopped down to f2.8. Light flare in image corners at open aperture.
Flare disappears when stopped down.
Combined synthetic-metallic mount. For a super wide angle sharpness and brilliance are very good. Also in the corners. Low for a lens of this angle. And heaven in a wildflower, Hold infinity in the palm of your hand And eternity in an hour.