Equipped with 2 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 2x the reach, get the most out of your Sigma lens.Optimized for Canon EF-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.