Optimized for Sigma SA-mount lenses in the Global Vision line, the TC-2001 2x Teleconverter from Sigma will offer an increase in focal length of 2 times for select Global Vision lenses. This model offers full communication between the lens and camera and will allows autofocus to operate at up to f/8. The teleconverter also features two Special Low Dispersion elements for reducing the appearance of chromatic aberrations and maintaining quality. Additionally, for protection, the TC-2001 is both dust and splashproof. When attached, the 2x conversion results in a light loss of approximately two stops. A soft zippered carrying case is included to protect the teleconverter when not in use