This Di lens is currently the most compact and lightest in the history of fast zoom lenses. Its compactness makes it look and feel like an ordinary standard zoom lens, yet provides the versatility that a fast constant maximum aperture offers and will definitely reshape photographic horizons. Features like LD glass elements and Internal Focusing put this lens in the same category of professional lenses as much bigger and more expensive Tamron lenses. LD glass elements reduces various aberrations while minimizing the fall-off of light at the corners. Features XR (extra refractive index) glass and efficient use of aspherical lenses.