TC-1401 1.4x Teleconverter from Sigma will offer an increase in focal length of 1.4 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 one Special Low Dispersion element for reducing the appearance of chromatic aberrations and maintaining quality. Additionally, for protection, the TC-1401 is both dust and splashproof. When attached, the 1.4x conversion results in a light loss of approximately one stop. A soft zippered carrying case is included to protect the teleconverter when not in use.Equipped with 1 SLD (Special Low Dispersion) glass element for maximum image quality, the new Sigma Global Vision teleconverters utilize a splash and dust proof construction for long lasting durability. Created exclusively for the Global Vision lenses, these teleconverters ensure the utmost in compatibility, even for large diameter lenses. With effective AF at F8 and 1.4x the reach, get the most out of your Sigma lens.