Sigma 17-50mm f/2.8 EX DC OS HSM Nikon DX Stabilized Fast Zoom Lens Hood
SIGMA 17-50mm f/2.8 EX DC OS HSM. - HSM (Hyper Sonic Motor): Fast, precise, silent autofocus. - Model: 17-50mm f/2.8 EX DC OS HSM. - AF Motor: HSM (Hyper Sonic Motor). This is what separates this lens from kit zooms.