Sigma 120-400mm f/4.5-5.6 DG OS HSM: Lens Test

This new supertele from Sigma is optically stabilized for handheld long-reach shots.

Clearly a sibling to Sigma's larger 150-500mm f/5-6.3 OS lens, this full-frame tele zoom ($850, street) is almost the mirror image of that longer lens, but about 25 percent smaller. It replaces Sigma's 135-400mm f/4.5-5.6 in the lineup, and it's a significant upgrade for a number of reasons: It uses Sigma's silent HSM focusing motor, is compatible with Sigma teleconverters, and, of course, includes Sigma's Optical Stabilizer. An 186-620mm equivalent when mounted on most DSLRs (that's 372-1240mm -- albeit without AF -- when used with a 2X teleconverter!), this lens incorporates three elements of super-low-dispersion glass for sharpness and is sold with hood, case, and a pretty cool tripod collar.

HANDS ON

The finish is Sigma's new ultra matte-black coat. Almost velvet-like, the surface looks prone to scuffing, but won't scratch (in normal use). Although the removable tripod collar is relatively large, it's cleverly designed with finger channels to help it double as an excellent grip for off-tripod shooting, even a good carrying handle for the lens and camera rig.

At 8.12 inches at its most compact, it's a big lens, but you can handhold its 3 pounds and 12-plus ounces easily due to smart positioning of zoom and focusing rings, and a pleasing balance overall.

The AF is near-silent thanks to the HSM AF motor -- and by the standards of such a long zoom, it's fast-focusing. In field tests, the AF system had no problem latching onto and following approaching cars, bicyclists, even pigeons. We suspect it would do well from gridiron sidelines or at waterside tracking soaring ospreys.

The amply sized zoom ring is somewhat stiff turning, but the smaller, well-placed manual-focus collar is nicely damped and a pleasure to use. Manual focus is possible in the lens' AF mode. Its barrel houses well-marked switches for AF/MF, the OS modes (on, off, and panning), plus a zoom lock at 120mm.

IN THE LAB

The lens delivered Excellent range SQF numbers at 120 and 250mm, indicating superior sharpness and contrast. As with most long tele zooms, however, it dipped into the Very Good range at 400mm. (By comparison, Sigma's 135-400mm plummeted into the Below Average range at 400mm.)

In DxO Analyzer 3.0.1 tests of the lens' distortion control, we detected only Imperceptible barreling at 120mm (0.04%) and Slight pincushion distortion at 250mm (0.12%) and 400mm (0.17%). These are very strong, almost flawless, numbers. And they're noticeably better than those of the 135-400mm, which showed Visible pincushioning at 300mm (0.90%), for example.

Light falloff was gone by f/6.3 at 120mm; by f/8 and 250mm and by f/10 at 400mm -- not great, but no worse than most.

The maximum magnification ratios at the uniform close-focusing distances of approximately 56.6 inches ranged from 1:9.7 at 120mm to 1:3.6 at 400mm. Such magnifying power bodes well, especially for nearby wildlife.

Tests of the Optical Stabilizer found that three unique users obtained sharp pictures at shutter speeds 2 to 2.5 stops slower with the OS engaged than without. We did find the OS action slightly jerky compared with Canon's IS and Nikon's VR, though.

CONCLUSIONS

Rather beefy but, on the whole, a delight to shoot with. Relatively easy to handhold in a pinch, and, because of the Optical Stabilizer, it's sharp. Certainly this lens is an excellent choice for distant wildlife or for moderately fast field sports like soccer.

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