If you are into nature and wildlife photography, you probably need an ultra-telephoto lens to photograph Singapore's smooth-coated otters or common plantain squirrels from afar without disturbing these animals. However, ultra-telephoto lenses tend to be big, heavy and expensive. For example, the Canon EF500mm f/4L IS II USM fixed ultra-telephoto lens costs $13,999 and weighs 3.87kg alone.

With Sigma's latest 150-600mm f/5-6.3 DG OS HSM Contemporary ultra-telephoto zoom lens, you no longer need to burn a hole in your wallet to buy one, or break your back to lug it around.

It provides a mouth-watering ultra-telephoto zoom range from 150mm to 600mm for $1,788 and has a modest weight of 1.93kg. It has built-in optical stabiliser (OS) and high-speed silent motor for fast auto-focusing (AF), plus a removable tripod collar and lens hood. The lens can be used with full-frame and APS-C DSLRs as well as film SLRs. It is available in Canon, Nikon and Sigma mounts. For this review, we used the Canon version with a Canon EOS 5DS (full- frame) and a Canon EOS 7D (APS-C).

For its price, the build quality is excellent. The lens feels solid and sturdy in your hands. I like the fact that this lens uses the rotating mechanism for zooming instead of the push-pull mechanism. The rotating mechanism is faster and more precise in reaching the desired focal length. A lock switch behind the zoom rotating ring prevents it from rotating, so you can stick to the focal length you want. Nice touch.

Closer to the camera body are four switches on the lens barrel, for Focusing, Distance, OS and Custom.The OS 1 mode is for static subjects while the OS 2 is for panning the lens to photograph moving subjects. In most situations, both modes worked well, allowing me to photograph sharp images hand- held with shutter speeds as slow as 1/100sec at 600mm. But anything slower than 1/60sec would cause motion blur at 600mm.

In terms of AF, it is not the fastest compared with fixed ultra-telephoto lenses. But it is quick enough in most situations for photographing wildlife. The image quality is great, considering the price. The lens delivers the sharpest images at 150mm with an aperture of f/8. Sharpness at the centre of the frame is superb and almost consistent throughout the aperture and focal length range. For such a long zoom, chromatic aberration is well controlled.

On the downside, the maximum aperture is not big enough. This translates to slower shutter speeds. You need to increase the ISO settings to prevent motion blur.

• Pound for pound, the Sigma 150-600mm f/5-6.3 DG OS HSM Contemporary gives the best value for money in terms of image quality, weight and AF.

Trevor Tan