The Sigma USB Dock allows users to connect their Canon fit Sigma Global Vision lenses to a computer to fine-tune and adjust parameters on their lens to suit their own personal preferences. Using Sigma's Optimisation Pro software (included) you can update the firmware and configure the autofocus speed (AF), optical stabilisation (OS), and modify the minimum and maximum focusing distance. The Sigma USB dock will not work with Sigma's existing lenses and has been specifically designed for their new line of lenses, such as the Sigma 17-70mm f2.8-4 DC Macro OS HSM, 35mm f1.4 DG HSM, 30mm f1.4 DC HSM, 18-35mm f1.8 DC HSM, 24-105mm f2.8 DG OS HSM, 50mm f1.4 DG HSM, 18-200mm f3.5-6.3 SC Macro OS HSM and 120-300mm f2.8 DG OS HSM lenses.