Sony's full-frame mirrorless camera line has been bolstered by the addition of the a9 body, which shoots at an incredible 20fps rate, but the system is a little light on telephoto lens options. The FE 100-400mm F4.5-5.6 GM OSS ($2,499.99) enjoys status as the lens with the longest reach in the family, and if you have enough light you can tighten its field of coverage further using a teleconverter. It's pricier than similar lenses for SLR systems, but backs it up with excellent image quality, a rock-solid build, and speedy autofocus.

Design

The FE 100-400mm ($2,498.00 at Amazon) is part of the G Master lens series, a designation Sony gives to its top-end lenses, designed to deliver excellent results on high-res image sensors, and to render out-of-focus areas with pleasing smoothness. It also means the lens is built tough—optics are housed in a gray metal barrel so you can feel comfortable shooting in rough weather. The front element is coated with fluorine, which helps to prevent oil and water from sticking to the glass—it's easy enough to wipe away fingerprints and rain drops.

The lens itself measures 8.1 by 3.7 inches (HD) at its shortest 100mm position, but extends when zoomed. It weighs 3.1 pounds, a bit lighter than Canon's EF 100-400mm f/4.5-5.6L IS II USM ($2,199.00 at Amazon) (3.6 pounds), and supports 77mm front filters. Sony includes a detachable tripod foot, mounted to a rotating collar, and a reversible lens hood. The hood has a sliding cutout window, a plus if you want to adjust the position of a circular polarizing filter.

The manual focus ring, covered in textured rubber for comfortable adjustment, sits right behind the front element. The zoom ring, with a similar finish, occupies a wider portion of the middle of the barrel and has markings at 100, 200, 300, and 400mm. There's a tension adjustment ring right behind the zoom control—when set to its tighter position you can still adjust the zoom, and the front element won't creep out when the lens faces downward. At the looser setting the zoom action is easier, but lens creep is an issue.

There are three focus hold buttons—at the 12, 3, and 6 o'clock positions—in the space between the focus and zoom rings. Holding any of them will prevent autofocus from activating when you take a photo, a good option if you want to override it for a single shot. There an AF/MF toggle switch if you want to set the focus mode for a longer series of images, along with a focus limiter that allows for the lens to hunt across its full range or only from 9.8 feet (3 meters) to infinity.

The in-lens stabilization system can be turned on or off with another toggle switch, and can be set to Mode 1, for shots when you're not moving the camera, or Mode 2, for situations where you're panning to follow a subject. Optical Steady Shot works in conjunction with in-body stabilization if your camera supports it. The system works well, especially in conunction with recent Sony bodies with in-body stabilization—handheld video at 400mm, captured from a sitting position, is not at all jittery.

The focus limiter speeds focus if you know you'll be shooting distant subjects only. But the focus motor is quite fast—even without the limiter enabled, the lens had no problems keeping up with the 20fps maximum capture rate of the a9 when photographing subjects running toward the camera.

The 100-400mm doubles as a near macro lens. At its maximum zoom and minimum 3.2-foot (0.98-meter) focus distance, it projects objects onto an image sensor at 1:2.85 life-size. We feel comfortable calling a zoom a macro if it's 1:3 or better, although you won't get full life-size reproduction and a true flat, distortion-free field of focus like you would with a dedicated prime macro lens.

The aperture is fairly dim, but you can use the lens with a 1.4x or 2x teleconverter if you need more reach. If you're happy with 400mm, and you already have an FE 70-200mm F2.8 GM OSS ($2,598.00 at Amazon) , pairing that lens with a 2x teleconverter—that is, turning it into a 140-400mm f/5.6 lens—might suit your needs. But I'm not sure how adding a teleconverter to the 70-200mm will impact sharpness or focus speed, two major concerns.

I have used the 1.4x teleconverter with the lens, along with the a9, at a nighttime soccer match under stadium lighting. The narrow aperture certainly comes into play—for most of its zoom range, the combination nets a maximum f/8 aperture. To freeze action under those conditions I ended up shooting at 1/1,000-second and pushing the a9 to ISO 12800. I was still happy with the results; the a9 delivers excellent high-ISO Raw images, and while there is certainly a grainy quality, the a9 didn't miss a beat focusing at f/8 and 560mm—even at 20fps.

Sony shooters also have the option of using Canon EF lenses via an adapter, like the Sigma MC-11, and there are more exotic telezooms available if you take that route. I'm a bit wary of using long zooms with the adapter, however, as my experience has been that autofocus performance suffers compared with native glass. I think you'd be better off adding an APS-C camera to your Sony kit, like the a6500, if you need to get more effective reach out of the 100-400mm than the lens and a teleconverter can provide together.

Image Quality

I tested the resolution of the 100-400mm using Imatest software and the 42MP a7R III camera. At 100mm f/4.5 the lens delivers excellent clarity, 3823 lines with fairly even performance across the frame. There's an improvement at f/8, 4,206 lines, which puts it in the outstanding range, and it maintains that level of quality at f/11 (4,136 lines). Diffraction cuts into resolution at f/16 (3,818 lines) and f/22 (3,208 lines).

The maximum aperture closes down to f/5.6 rather quickly. It hits f/5 at 119mm and f/5.6 at 164mm. We next tested resolution at 200mm f/5.6 and the lens shows 3,782 lines, again with excellent image quality right up to the edge of the frame. There's an improvement at f/8 (4,206 lines) and f/11 (4,136 lines), and we start to see a dip at f/16 (3,818 lines) and f/22 (3,208 lines).

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The story is the same at 300mm—the lens is excellent at f/5.6 (3,395 lines), f/8 (3,929 lines), f/11 (3,952 lines), and even at f/16 (3,795 lines), but loses a step at f/22 (3,132 lines). The numbers aren't that far off at the maximum 400mm setting. At f/5.6 we see 3,779 lines, which improves slightly at f/8 (3,997 ilnes), f/11 (3,687 lines), and f/16 (3,616 lines), before taking a small step back at f/22 (2,975 lines).

In the real world, this means you can shoot the 100-400mm from wide open down to f/11 and net extremely crisp images. And if depth of field calls for it, diffraction doesn't do too much to harm image quality at f/16 or f/22, though I'd try and avoid f/22 to stay on the safe side.

There's a little bit of pincushion distortion when zoomed. We don't see enough to worry about in the real world at 100mm (0.4 percent), but it hovers around 1.5 percent at 200, 300, and 400mm. You can eliminate it via an automatic in-camera correction if you shoot in JPG format, and Raw photographers can use Lightroom for one-click lens profile corrections.

There is a loss of illumination at the corners of the frame when compared with the center. Imatest's Uniformity analysis shows a 2-stop (-2EV) drop from center to corners at 100mm f/4.5, which gives photos a noticeable vignette. The deficit is cut to -1.5EV at f/5.6, and is negligible at f/8 and narrower, where it falls under -1EV.

At 200mm f/5.6 we see a -1.3EV drop, but at narrower apertures the difference isn't visible. The story is about the same at 300mm f/5.6 (-1.7EV), but the vignette increases at 400mm. At f/5.6 there's a -2.3EV drop at the corners and it's still -1.7EV at f/8—it doesn't go away until f/11. This testing was done with illumination correction turned off in-camera, so if you shoot JPGs you can leave it turned on and the effect will be compensated for automatically. The same Lightroom profile that corrects distortion for Raw images corrrects illumination, so you can use that if you incorporate Lightroom into your Raw workflow.

Conclusions

The FE 100-400mm delivers excellent image quality, a pro-grade build, fast autofocus, and strong image stabilization. There's a little distortion and some corner dimness to contend with, though both are easily removed with some light editing. But you pay for it—it's the most expensive 100-400mm of this type that we've seen. For photographers who need the range it's a worthy purchase, but be prepared to push your ISO high when shooting in dimmer conditions, especially if you need to add a teleconverter.

Sony has a 400mm F2.8 GM lens coming out next year for photographers who need long telephoto reach and a wide aperture, but it's expected to be very expensive, and you can't discount the importance of zoom adjustment when shooting sports from the sideline. If you're on a budget, don't forget about the FE 70-300mm F4.5-5.6 G OSS—it doesn't have quite the reach or teleconverter compatibility, but is priced much lower.

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