Kenko Teleplus Pro 300 DGX converters are made with precision quality multi-coated optical glass supplied by Hoya Corporation. These glass elements were designed to match the optical quality of the prime lens (even at the edges) and telephoto zoom lenses. The optical design of the elements and light path is wide enough not to cause vignetting. The PRO 300 is designed specifically to be used with prime telephoto lenses of 100 mm or above, such as 300 mm f/2.8 lenses, and work best with telephoto lenses of 200 mm to 500 mm. The PRO 300 can be used with telephoto zoom lenses as well as prime lenses.