Although not as fast as the Canon EF 16-35mm f/2.8L lens, the Canon EF 17-40mm f/4L USM Lens is a comparable lens in terms of image quality. The biggest difference between the 17-40 and the similar-focal-length-covering 16-35 L is price.
Principais Características. A clássica lente grande-angular da Série L ganha uma versão mais aprimorada e refinada. A nova EF 16-35mm f/2.8L III USM garante performance surpreendente e superior para este clássico 'range' 16-35mm mantendo sempre a luminância ótica da abertura máxima constante de f/2.8, em qualquer de suas distâncias 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 340 g Max. Diameter x Length 89 mm x 79.2 mm 83.5 mm x 68.9 mm Groups/elements 12/15 What your seeing is normal for a USM lens with mechanical AF override. The focus ring will continue turning 360 degrees. Have you ever used an EF Mount USM lens. Almost all of them work this way. Micro Motor USM lenses DO NOT support MF override. Except the EF 50mm F/1.4 USM lens. It has an additional clutch system to allow MF override just (I have the 20-35mm L, 28-70mm L and the 70-200 L) and (2) it was $600 leass than the newer 16-35mm that replaces it. So I conducted an in-depth comparison between the 17-35mm, 20-35mm, and 28-70mm lenses. EwwCW.