Review manufacturer specifications and detailed lab measurements for the Canon EF 17-40mm f/4L USM Lens. Compare the specs and measurements of this lens with other lenses. Canon EF 17-40mm f/4L USM Ultra Wide Angle Zoom Lens for Canon SLR Cameras (Renewed) Canon EF-S 10-18mm f/4.5-5.6 is STM Lens, Lens Only Sigma 18-35mm F1.8 Art DC HSM Lens for Canon, Black (210101) Compared to the Canon EF 17-40mm f/4 L USM Lens. There are not many direct competitors to the Tokina 17-35 from a full frame perspective. The Canon EF 17-40mm f/4 L USM Lens is the most logical lens to alternatively consider. I spent a lot of time shooting comparisons between these two lenses, but with complicated image quality, making these Pros Ultra-wide field of view. Reasonable price tag. Good center sharpness. Cons Muddy edges and corners at 17mm. Some distortion. Noticeable color fringing. The Canon EF 17-40mm f/4L USM Canon EF 17-40mm f/4L USM Lens Image Quality (the-digital-picture.com) Side note: I have found the site is a little iffy with lenses shot wide open at f/8 though it seems pretty representative of reality. The above link is shown on the 5Dsr which is 50mp. Looks pretty good. The EF 17-40mm f/4L USM lens is a member of a suite of Canon zoom lenses that retain a constant f4 maximum aperture throughout the zoom range. Designed for use on 35mm SLR cameras, this ultra-wide zoom is ideal for capturing dramatic landscape shots and taking portraits of large groups of people. It will also prove useful for shooting in cramped interiors. [ia] This is a big drop in quality all around, IMHO, of course. In the first place it is not a constant aperture. A 135mm lens @ f5.6 is nothing to brag about when comparing to the other choices stated. The constant f2.8 aperture is a huge plus. Actually the main most reason for the ef-s 17-55mm f 2.8 IS USM. shooting with a 17-40mm f/4L. I've heard two different stories though - some people say that the 25mm is better for a wide lens, but some people say otherwise. One review says that "The Canon EF 25mm Extension Tube II is recommended for lenses with a focal length of 50mm and up," but another article rATuTd.