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Design

The 70-200mm F2.8 OS is somewhat unconventional in design for a lens of this type. Most notably, the zoom ring is positioned towards the front of the barrel, with the unusually slim manual focus ring immediately behind it (all other fast telezooms place the zoom ring towards the center of the barrel, with the focus ring up front). The switches that control the autofocus and stabilization systems are in the usual place, though, inhabiting a prominent panel on the left side of the lens.

Cosmetically, the lens also represents a departure from Sigma's EX designs of the past decade. The relatively slimline barrel mainly eschews the familiar crinkle-effect coating in favor of an understated matte-black paint, although the old finish is still found on the zoom and focus rings and the tripod collar. The overall affect isn't quite as harmonious as before, although it's not unattractive.

The construction quality is difficult to fault, given that the price is substantially lower than the Canon and Nikon equivalents. Those matte-black barrel shell components are plastic, not metal, but really little the worse for it - the lens feels robust with a high standard of fit and finish. Both the zoom and focus rings are smooth in operation, and the large autofocus and optical stabilization switches operate in a positive fashion.

Last but not least, the tripod collar design is inherited from the old unstabilized 70-200mm F2.8, which is welcome because as far as we're concerned it's pretty much the best in class.

On the camera

Like all lenses of this type the Sigma is a sizeable beast, and handles best on larger bodies. It's perhaps most at home on professional DSLRs such as the Canon EOS-1D(s) or Nikon D3 series, and it positively dwarfs the current breed of compact bodies, illustrated here by the EOS 550D. Handling on this kind of small camera is hugely improved if you add a vertical grip, especially if you do a lot of portrait-format shooting.

The most unusual aspect of the handling is the zoom ring, which is situated right at the front of the lens. In practice we've found this works perfectly well, and effectively eliminates any need to rotate the tripod foot out for the way for hand-held shooting. But if you're used to grabbing the ring at the front to tweak focus, you'll have to re-train yourself for this lens.

However, there is one small caveat. The 70-200mm comes with a huge hood, and when reversed this obstructs all of the controls; most importantly the zoom ring becomes completely inaccessible, however both the focus ring and the AF and OS mode switches are partially blocked too. So if you pull the lens out for your bag for a quick grab shot with the hood reversed, you won't be able to zoom (uniquely for a 70-200mm F2.8). For many users this will be a complete non-issue, but for a few it could be a concern.

Autofocus

This lens features Sigma's ultrasonic-type hypersonic motor for autofocus, which performs extremely well. It's practically silent in operation, and we found it to be fast and accurate in everyday use with no evidence of any systematic focusing errors using a number of Canon test bodies (including the EOS 5D Mark II and EOS 7D). We also tried out the lens's continuous AF capability by shooting fast-moving track cyclists using the EOS 7D at 7fps, and found AF tracking to work very well, with an impressive return of in-focus 'keepers'.

As usual, though, it must be noted that focus speed and accuracy is dependent upon a number of variables, including (perhaps most importantly) the camera body used, subject contrast, and light levels.

Change in angle of view on focusing ('focus breathing')

The Sigma 70-200mm F2.8 OS gives a wider angle of view on focusing closer, in a somewhat similar fashion to Nikon's 70-200mm F2.8 VR II, although to a lesser extent. By our reckoning, at closest focus the image field is about 1.1x larger in each direction, making the effective focal length roughly 180mm at 1.4m. A side-effect of this is the maximum magnification of 0.13x, which is slightly low for this type of lens.

Lens body elements

The lens will be available in Canon, Nikon, Pentax, Sigma and Sony versions. Our review sample was in the Canon EF mount.

One noteworthy difference compared to the much-more-expensive Canon and Nikon equivalents is the lack any sealing around the lens mount - this isn't a lens that's designed to withstand prolonged use in the rain.
The filter thread is 77mm, which has become the de facto standard for professional lenses. It does not rotate on autofocusing, which is good news for users of filters such as polarizers.

This frankly vast bayonet-mount lens hood comes in the box. It's no less than 10.7cm (4.25") deep, and has molded ribs on the inside to minimize reflection of stray light into the lens. It's even got a grip on the outside to aid removal from the lens.

The hood reverses for storage, but it does then completely block the zoom ring, and partially obstruct the other controls too.

You also get this hood extension for use on APS-C cameras, that adds an extra 2.5cm (1") of shading.

This is a great idea in principle, but has problems in practice. To store the hood you're supposed to reverse it over the extension. But we found that when you remove the hood again to use the lens, the extension comes off as well, stuck inside, and you then have to extract it. We ended up leaving it at home.
The zoom ring rotates 60 degrees anti-clockwise from 70mm to 200mm, i.e. the 'right' way for Canon users, but opposite to Nikon, Pentax and Sony lenses. The ribbed rubber grip is 53mm wide, and the zoom action extremely smooth and precise.

In common with other 70-200mm F2.8 lenses, the zoom action is entirely internal.
The manual focus ring is distinctly slim - the ribbed grip is just 8mm wide - and rotates about 110 degrees clockwise from infinity to 1.4m (this time the 'right' way for Sony and Canon users, but opposite to Pentax and Nikon lenses).

It does not rotate during autofocus, and the full-time manual system allows tweaking of the focus even when the lens is set to AF. Again the action is smooth and precise.
A distance scale is provided with markings in both feet and meters, and the focus ring travels slightly past the infinity mark, apparently to allow for the effects of ambient temperature variations.

Unusually for a telezoom (but like Sigma's older 70-200mm F2.8) there's also a depth of field scale with markings for the Wide and Tele positions...
...but the problem with this scale is that, due to the lens's rear-focusing design, the indicated depth of field at short distances becomes highly inaccurate (and over-optimistic).

Here it appears to be suggesting that at 70mm, F22, and a focus distance of 3m, objects from 1.4m to just shy of 10m will be acceptably sharp; most depth of field calculators will tell you 2.1m to 5m instead.
This prominent panel on the side of the barrel plays host to the focus and stabilization mode switches.

The OS switch has three positions; 'Off', '1' for stabilization in both axes, and '2' for stabilization in one axis only (for use when panning). Sigma warns OS should be switched off when the lens is used on a tripod.

Note there's no focus limiter switch.
The lens uses the same tripod ring as its unstabilized sibling, which is welcome because it's one of our favorites. 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.

Marks at 90 degree intervals around the lens barrel aid alignment for vertical shooting.
Finally, a nice touch is the addition of this ribbed segment on the side of the barrel, which provides a firm grip when taking the lens on and off the camera. This is most helpful when, as here, the tripod collar is detached.

Reported aperture vs focal length

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

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