Sigma TC-2001 2x Teleconverter for Sigma SA (only for SGV Lenses)The TC 2001 from Sigma is a 2x Teleconverter specifically designed for Sigma SA mounts. Designed with 2 Special Low Dispersion glass elements, you will experience superb image quality. This teleconverter increases the focal length by 2x for select Global Vision Sigma lenses. It employs full communication between the lens and camera, allowing the autofocus to operate at up to f 8. Sigma constructed this teleconverter to be dust and splash proof so you