Sigma's USB dock is a unique accessory, that was announced as part of Sigma's 'Global Vision' strategy at Photokina 2012. It's a pretty simple concept - it allows you to plug a lens into a computer and update its firmware or tweak its operational settings using Sigma's 'Optimization Pro' software. It would be easy to think that because nobody else offers such a thing, it must be superfluous. But look a little closer and it's actually an interesting piece of kit. In this review we'll look into how it works, and what it can do.