You can control the performance of Sigma lenses with ease using the Sigma USB Dock ($59 at Amazon). Compatible with all recent company glass, the Sigma USB Dock ($59 direct) allows you to take full control of your Sigma lenses. You'll be able to tell if your lens belongs to this line by its Contemporary, Art, and Sports designations.
This is available for Sigma, Nikon and Canon mount lenses. It currently includes five lenses. Only one lens, the 120-300mm DG OS F2.8 DGOS HSM (Amazon: $3,549.99). This is the only lens that's compatible with all customization options.
The 35mm F1.4DGHSM ($674.95 on Amazon), 17 to 70mm F2.8-4 DC Macro OShSM, 30-mm F1.4 DC DC HSM and 18 to35mm F1.8 DCHSM($659.95 on Amazon). It is compatible with OS X as well as Windows. The lenses all support focus adjustment and firmware updates. While firmware updates can be explained easily, focus adjustment requires an understanding of the camera's autofocus mechanism.
The mirror bounces light from one end to the other. Although it would be ideal if every camera made by a particular manufacturer was perfectly calibrated, the reality isn't perfect. Lenses that are not designed for critical use often have issues with back-focus and front-focus. This is when the lens is slightly behind or in front of their subject.
You can correct a lens focus problem by adjusting the body and lens. Higher-end cameras may support in-camera focus adjustments. However, they are not as powerful as software that is compatible with the dock. You can set the focus distance and focal length.
All other functions will only work with the 120-300mm lens at the moment. You can adjust how the lens stabilizer system operates by using an OS setting. Three modes are available: Dynamic, Standard and Moderate. Dynamic view shows how the stabilization system affects the viewfinder. It moves elements as fast as possible in order to capture quick action.
Moderate View reduces the speed of the stabilization system and makes it less noticeable when taking time to create a scene. Standard mode, which is the default behaviour of the lens, lies somewhere between the extremes.
You can choose to prioritise speed or accuracy. Or you can revert back to the default setting which is somewhere between the two. The Focus Limiter allows you to limit your focus distance over any distance. You can limit the focus range from 50 feet up to infinity if you are shooting a sport event. The focus limiter function can only be activated on lenses with a toggle switch that allows you to disable or enable it. This will allow you to focus across all of your lens' range in the field.
It is not an accessory every photographer will need or use. The functionality of the Sigma USB Dock depends on what lens you are using. It's an affordable way to calibrate your lens if it isn't focusing properly. You will find the most advanced functions with the 120-300mm Telephoto Zoom.
Future long telephoto or macro lenses will benefit from the autofocus speed and focus limiter. Although it is easy to use, you should take care when calibrating focus. It's an affordable accessory for $60 and a great tool to keep if your Sigma lens is compatible.