The Canon EF 24-70mm f/2.8 L USM Lens is a very sharp lens – few zoom lenses reach this level of sharpness. The 24-70 L is sharp in the center at f/2.8 at all focal lengths and performs very well in the corners. Some corner softness is visible at the wide end of the focal length range and more softness is apparent in the 50-70mm corners. As usual, stopping down (selecting a narrower aperture) to f/5.6 makes a big difference in the longer focal length corners.
The wide open 24mm corners are most-affected by vignetting. Vignetting is very well controlled, but apparent in the corners at f/2.8 at 24mm on a full frame body. Vignetting improves as the focal length increases and the aperture is narrowed. At comparable apertures, the 24-70 L shows less vignetting than the also-excellent Canon EF 24-105mm f/4 L IS USM Lens – a typically-expected result when comparing a fast lens to a slower lens.
Like most 24-xx zoom lenses, the Canon EF 24-70mm f/2.8 L USM Lens shows some barrel distortion on the wide end. More specifically, a bulge in the middle of the frame. Barrel distortion disappears around 35mm. A very slight pincushion distortion begins at 50mm and becomes moderate by 70mm.
Color, contrast and saturation are excellent. CA (Chromatic Aberration) is very well controlled – especially for a zoom lens. The wide 8-blade aperture produces a nice quality background blur and a nice amount of it.
Prime lenses (fixed focal length lenses) are often compared favorably to the Canon EF 24-70mm f/2.8 L USM Lens. They are generally less expensive, smaller, lighter, faster (aperture) and very sharp. My personal preference is for zoom lenses for my photography applications in this focal length range. To me personally, the ability to change framing instantly far outweighs the slight image quality advantages fixed focal length lenses offer over the 24-70 L.
I’m often asked – can images shot with a consumer zoom lens be post-processed to result in images similar to 24-70 L images? The answer is: you can adjust contrast and saturation, but you cannot add missing detail. And, color can be very difficult to match later. So, using a better lens will usually result in better post-processed images. Most primes and L lenses are noticeably better than consumer zooms.
Image quality is not the only pro-grade feature of the Canon EF 24-70mm f/2.8 L USM Lens. Excellent AF is part of the equation. A Ring USM (Ultrasonic Motor) AF system delivers quiet, fast and accurate autofocus. The 24-70 L’s f/2.8 aperture enables the enhanced-sensitivity of many Canon EOS DSLR body’s AF points. As usual for a Ring USM AF system, FTM (Full-Time Manual) focusing is enabled. The 24-70 L does not extend with focus and the 77mm filter ring does not rotate.