This is a SIGMA lens that is equipped with auto focus to give you the best setting for each picture. If you want to use a filter on the lens, then the filter size is 77 mm.
From London Camera Exchange
Sigma 85mm f/1.4 DG DN ART - For F/L Mount
Bristol Cameras
Sigma 85mm F1.4 DG DN | Art Lens L-Mount Fit
This product is also available at 3 unverified stores.