The Kenko Teleplus Pro 300 DG converters are made with precision quality multi-coated optical glass supplied by Hoya Corporation, the world's largest manufacturer of optical glass. 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 family is designed specifically to be used with prime telephoto lenses of 100mm or above, such as 300mm f/2.8 lenses, and works best with telephoto lenses of 200mm to 500mm. The Pro 300 can be used with telephoto zoom lenses as well as prime lenses. However, Kenko does not recommend them for zoom lenses that have a range starting under 50mm.
The Pro 300 AF Teleplus converters have genuine Gate Array IC (Integrated Circuitry). It means that the converter’s own unique circuitry maintains signal integrity between the camera body and lens. These converters are designed to electronically operate the same way as an original manufacturer’s converter.
Corner resolution is stellar and deterioration of light is kept to the absolute minimum. Due to the 3 stop light loss inherent in a 3x converter, Kenko PRO 300 3.0x has no AF capability. The lens must be focused manually.