The Teleplus PRO 300 converter is made with high quality multicoated optical glass supplied by Hoya Corporation, the worlds largest manufacturer of optical glass. The PRO 300 3x is designed for use with lenses of 50mm or above and work best with telephoto lenses of 100mm to 500mm. The PRO 300 3.0x can be used with telephoto zoom lenses as well as prime lenses. However, Kenko does not recommend them for lenses that have a zoom range that starts under 50 mm. Important Note: Due to the 3 stop light loss inherent in a 3x converter, Kenko states that the PRO 300 3.0x converter will not auto focus with lenses that have a smaller aperture than f/2.8. With all lenses having apertures smaller than f/2.8, Kenko recommends using the PRO 300 3x in manual focus mode.