The SIGMA 85mm F1.4 DG DN | Art lens for Sony E-Mount is designed exclusively for mirrorless cameras, it has a “large lens diameter and superb optical performance” and “a lightweight and compact body,” a combination which has long been difficult to achieve.
The AF motor system employs a stepping motor which is optimized for both phase detection AF and contrast AF. Not only does this provide a smooth shooting experience only possible with a mirrorless camera, such as face/eye detection AF, but it has also made the lens body itself much smaller, as the focus lens has been made small to better suit a stepping motor.