Sigma 18-200mm f/3.5-6.3 DC OS - £290
Sigma's 18-200mm lens is bigger and heavier than some lenses with a mightier zoom range, including the Sony 18-250mm and Tamron 18-270mm. Indeed, it has almost exactly the same dimensions as the Sigma 18-250mm. When you're looking for a lens that's compact and lightweight for travel, yet delivers a generous zoom range, the Sigma 18-200mm is disadvantaged immediately.
The maximum aperture of f/6.3 is also a bit disappointing, being half a stop slower than the Canon and Nikon 18-200mm lenses. At least lenses that offer focal lengths up to 250mm or 270mm have a more compelling reason for the extra half stop. It also lacks the quiet HSM autofocus system found in Sigma's newer 18-250mm option. The standard micro motor in this lens is quite shrill and noisy.
Optical stabilisation is below par compared with other stabilised lenses in the group, because as one of Sigma's first stabilised lenses to hit the market, the 18-200mm features an old-generation system. In our tests, it gave an advantage of only between two and three stops.
The build quality feels pretty high, but the zoom ring goes through a nasty stiff patch in the middle of its travel. However, there's practically no zoom creep, and the lens also features a zoom lock. Optical quality for sharpness, lack of colour fringing and distortion proved average across the board.
Centre sharpness across the range is good, just beating the Sigma 18-250mm, but there's a steep fall-off towards the edges.
There's a slight red fringe towards the edges at 18mm, and green at 200mm. However, the effect of fringing overall is minimal.
The influence of barrel and pinch distortion are more pronounced than on the 18-250mm, but results show an average score.
Image test verdict
Centre sharpness is not far behind the 18-250mm. It copes well with distortion and fringing, but edge sharpness suffers at all focal lengths.