First wide-angle to standard zoom lens to achieve a large aperture of 1.8 Due to the very shallow depth of field (DOF) of fast glass and focus variation between the cameras, users may experience focus shift and inconsistent AF. This can be fixed by using the AF fine tune ( For Nikon System) or AF Micro Adjustment( For Canon System) in the camera's Menu to calibrate the lens to specific cameras. Also shooting at smaller aperture values will increase the DOF which reduces “focus issues” as the result of the variations and decreases the amount of fall of (Vignetting).