Canon EF 24-70mm f/4L IS USM

Pros Optically stabilized. Sharp throughout the zoom range. Optically stabilized. Macro mode at 70mm.

Cons Some distortion at 24mm. Telescoping design. Bottom Line If your demands don't require a fixed f/2.8 zoom lens, the Canon EF 24-70mm f/4L IS USM will reward you with sharp images and a useful zoom range.

By Jim Fisher The Canon EF 24-70mm f/4L IS USM ($1,499 list) is a wide-to-short telephoto zoom lens for Canon cameras. It's noticeably smaller than the EF 24-70mm f/2.8L II USM, a lens that captures twice the light at its widest aperture, but lacks image stabilization and is priced around $2,300. Image stabilization will help you get a sharp shot of a static subject, but event shooters who need to capture as much light as possible will likely be drawn in by the allure of the more expensive optic.

If you can live with an f/4 lens, though, you'll be happy with this zoom. It measures just 4.4 by 3.5 inches (HD) and weighs 1.8 pounds. The lens has a large front element, it accepts 82mm filters, and includes a reversible petal-style lens hood. The lens extends as you zoom in, an anomaly when compared with other top-end lenses with internal zoom designs. Thankfully there is a lock switch to hold the lens to its shortest position so that it's more secure when stowed.

It can focus as close as 15 inches throughout its zoom range, but there's a special macro mode (activated by an on-lens switch and a twist of the zoom barrel) that allows the lens to lock on to objects as close as 7.9 inches from the camera's image sensor at 70mm. That's about 1:1.4 magnification, so you can't fill the frame with a small object as you can with a macro lens that supports 1:1 magnification, but it's impressive for a zoom. You'll want to remove or reverse the hood when working with macro subjects, as the minimum focus distance is very close to the front element of the lens.

I used Imatest to check the sharpness and distortion characteristics of the lens when paired with the full-frame EOS-1D X. It's an impressive performer all around, delivering a center-weighted resolution score better than 1,800 lines per picture height at every tested focal length and aperture, and also maintaining that level of detail at the edges of the frame, an area where image quality often suffers.

At 24mm the center-weighted score is 2,401 lines, with edges that hover just under 2,000 lines. Stopping down to f/4.5 improves the overall score marginally to 2,452 lines, and edges jump to 2,154 lines. Barrel distortion at this setting is 1.9 percent, not out of line for a zoom of this design, but it's a bit more than the 1.3 percent exhibited by the excellent Sony Carl Zeiss 24-70mm f/2.8 zoom. Lightroom 5 includes a lens profile for this zoom, so you can correct for the distortion with a single click.

There's no distortion a 35mm, and the lens still manages an impressive 2,418 lines here with edges that hover around 2,200 lines; that's an impressively even result across the frame. At f/5.6 the average score is 2,472 lines and edges are 2,417 lines. Zooming to 50mm introduces about 0.7 percent pincushion distortion and the resolution drops to 2,069 lines at f/4. Edges are ever slightly soft here, 1,727 lines, but stopping down to f/5.6 improves them to 1,896 lines and bumps the average score to 2,296 lines.

Sharpness at 70mm is also impressive, and there's only 1 percent pincushion distortion. The lens manages 2,350 lines at f/4, with edges that near 1,900 lines; stopping down to f/5.6 only marginally improves this impressive result. Overall the lens is a better performer than the Sigma 24-70mm F2.8 IF EX DG HSM; its sharpness suffers at its maximum aperture, though it does improve as you narrow the aperture.

If you're in the market for a zoom lens for your full-frame Canon camera, the Canon EF 24-70mm f/4L IS USM is a solid choice. It's optically stabilized, sharp, and has a very impressive macro mode. Its telescoping design may be a turnoff for some shooters, but it does allow the lens to be a bit more compact when retracted compared with others with internal zoom designs. Event shooters will likely find the f/2.8 version of the lens more useful, as light is a premium and fast shutter speeds are always appreciated when covering weddings, but if you can handle an f/4 lens, this is a good one.

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