Design

The 70-200mm F2.8 is a member of Sigma's premium 'EX' lens line, and build quality feels genuinely excellent, especially for the price point. This is a lens which feels more refined in fit and finish than its Tamron counterpart, and certainly appears sufficiently solid and robust to stand up to some fairly heavy use and abuse. However it doesn't match the sheer level of 'bombproof' build attained by the Canon and Nikon designs, and lacks the same degree of sealing and environmental protection (for instance, there's no lens mount seal); as so often in life, you get what you pay for.

This lens is the shortest in its class, but has a relatively broad barrel especially towards the rear of the lens, placing it at the opposite end of the design spectrum to the long, slim Nikon. It's still pretty sizeable by most users' standards, and therefore potential upgraders should appreciate that it's significantly larger and heavier than consumer telezooms such as 70-300mm F4-5.6s. It's unlikely to be the ideal travel lens for most users, no matter which city or country they're visiting.

On the camera

Like all of the 70-200mm F2.8s, this is a large lens and handles best on enthusiast or professional cameras; above left we see it mounted on the Nikon D3. The balance of the lens is excellent, with the zoom ring well-placed with respect to the centre of gravity, and the large manual focus ring within easy reach. Like all 70-200mm F2.8s, it's not an ideal match to the current crop of miniaturized entry-level dSLRs such as the Nikon D60 (above right), although still quite useable. With its built-in AF motor, it's also fully compatible with Nikon's D40-D40x-D60 series of budget SLRs.

Autofocus

This lens uses Sigma's 'HyperSonic Motor' (HSM) variant of ultrasonic focusing for fast, accurate and near-silent operation. The good news is that this will be provided for users of all lens mounts, but unfortunately it also means that users of older Pentax DSLRs which don't support SDM lenses will lose out, and only be able to focus manually (in other words, the lens is effectively of KAF-3 mount specification).

In real life use, our Nikon-mount sample performed well, with AF fast and positive under all but the most difficult conditions (using a variety of bodies from the D60 to the D3); as always, it must be noted that focus speed and accuracy is dependent upon a number of variables, including the camera body used, subject contrast, and light levels. The major problem we found with focusing this lens was a shift in the field of focus on stopping down, which was especially visible at 200mm and close distances; this is a symptom of spherical aberration, and causes problems for any open-aperture focus system, auto or manual (this is discussed in greater detail later in the review). However at middle to longer distances, focus was generally accurate and consistent, and was also fully able to track fast-moving subjects when used in continuous AF mode.

Lens body elements

The lens will be available in mounts for all currently available DSLRs (Canon, Nikon, Sony, Pentax, Sigma, and Four Thirds); our sample here is the Nikon F version.
The filter thread is 77mm as is typical for lenses of this type, and does not rotate on autofocusing (which should be welcome for filter users).
The 80mm/3.1" deep petal-type lens hood features moulded internal ribs to minimize the reflection of stray light into the lens, and reverses neatly for storage.

The hood fits to the front of the lens via a bayonet mount; for those who struggle with such things, Sigma has helpfully included alignment dots plus arrows marked 'In' and 'Out' indicating the direction you need to turn it. Nice.
The zoom ring rotates 80 degrees clockwise from 70mm to 200mm, i.e. the 'right' way for Nikon, Pentax and Sony users, but opposite to Canon and Olympus lenses. The ribbed rubber grip is 23mm wide, and the zoom action smooth and well-damped.
The focus ring is 37mm wide, does not rotate during autofocus, and again the action is smooth and precise. It rotates 140 degrees clockwise from infinity to 1m (this time the 'right' way for Sony, Olympus and Canon users, but opposite to Pentax and Nikon lenses). This is substantially longer travel than the Tamron, which makes precise manual focus much more straightforward. The angle of view noticeably decreases on focusing closer.
Canon users will find a conventionally placed switch on the side of the lens barrel to select between auto and manual focusing modes.

Because the lens uses a ring-type ultrasonic focus motor, all users will benefit from 'full-time' manual focus, with the ability to tweak the focus setting even when the lens is set to AF.
A distance scale is provided with markings in both feet and meters. Sigma have also included a depth of field scale, with the caveat (hidden away in the user manual) that it's only valid at 70mm. A little playing with depth of field equations also indicates that it's been calculated for the 35mm full frame format, so it won't be terribly useful for the majority of users (and could be downright misleading for some).
The lens comes with a detachable tripod mount ring, which is lined with a Teflon sleeve for smooth rotation. The line at the top aligns with marks arranged at 90 degrees around the lens for landscape and portrait formats.

The clever hinged design allows rapid removal when the lens is fitted to the camera; simply twist the knob to loosen the ring for rotation, and pull it outwards to release the ring altogether.

Reported aperture vs focal length

This lens allows an aperture range from F2.8 to F22 at all focal lengths.