The PRO 300 3x is an auto-exposure, manualfocus converter 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.