The Sigma USB (Universal Serial Bus) Dock allows users to connect their Pentax fit Sigma Global Vision lenses to a computer to fine-tune & adjust parameters on their lens to suit their own personal preferences. Using Sigma's Optimisation Pro software (included) you can update the firmware & configure the autofocus speed (AF), optical stabilisation (OS), & modify the minimum & maximum focusing distance. The Sigma USB (Universal Serial Bus) dock will not work with Sigma's existing lenses & has been specifically designed for their new line of lenses, such as the Sigma 17-70mm f 2.8-4 DC Macro OS HSM, 35mm f 1.4 DG HSM, 30mm f 1.4 DC HSM, 18-35mm f 1.8 DC HSM, 24-105mm f 2.8 DG OS HSM, 50mm f 1.4 DG HSM, 18-200mm f 3.5-6.3 SC Macro OS HSM & 120-300mm f 2.8 DG OS HSM lenses.