Since many users shoot mainly with a Nikon D750 full-frame, the lens bundled with a 1.4x Teleconverter interested many people. The Sigma TC-1401 1.4x Teleconverter allows a full-frame camera to shoot wildlife with almost the same zoom factor as a crop sensor. It is compatible with a range of lenses such as 60-600 mm f/4.5-6.3 DG OS HSM Sports, 150-600 mm f/5-6.3 DG OS HSM Contemporary, and 500 mm f/4 DG OS HSM Sports. Our take on the Sigma TC-1401 1.4x Teleconverter for Nikon F Lens: The Sigma has a larger, thicker focusing ring that makes it quite easier to focus the lens attached to the camera manually. It has an extra setting for manual override (MO) on the autofocus switch, which means it combines autofocus with an option to focus manually. The lens has a focus limiter switch, with settings between Full and 10m (Sigma) to infinity. The Sigma for 10m to 2.8m provides a feature of a third option on the limiter switch. The third option proves easy and very useful to locate and use in order to focus on closer objects much quicker. A key feature that the Sigma lens offers is an extra customization switch, which provides for an optional USB docking station that can be purchased separately. It allows a photographer to create two customized settings for OS (Optical Stabilization), AF, and focus-distance limits, and can also be used to download firmware updates directly to the lens.