In the side by side image you can see the size difference in the two lenses. The 17-40mm lens is 0.63 inches shorter and weighs about 0.3 lbs less than the 16-35mm lens. The 16-35mm f/4L IS USM lens has 16 elements in 12 groups while the 17-40mm lens only has 12 elements in 9 groups. The 16-35mm f/4L IS USM is FULLY weather sealed while the 17
f /2.8L f /3.5–4.5 Image Key features Image stabilizer No Environmental Sealing No USM No Yes L-series Yes No Diffractive Optics No Technical data Maximum aperture: f /2.8 f /3.5–4.5 Minimum aperture: f /32 f /22–27 Filter diameter 72 mm 77 mm Horizontal viewing angle: Vertical viewing angle: Diagonal viewing angle: Physical data Weight 570 g HnFpqsX.