Photo answers review
Photo answers rating 
Features & handling Sigma uses 15 elements in 13 groups to make up this lens. There are seven diaphragm blades – quite common among the lenses here. The general build is neat and very compact. This is a feature that makes the lens attractive as an upgrade, because it’s a lightweight lens compared to some in this test. The focus and zoom rings have a good, fluid movement.
Performance General sharpness is average on this lens, and edge definition isn’t too bad. Edges get very soft with wider apertures, especially at the shorter zoom settings. At f/11, with the focal length around 50mm, you get the sharpest performance. Considering the price of this optic, it’s a reasonable buy for £320, but the f/2.8 aperture is best avoided if you want the sharpest shots.
At the 50mm end of the focal length range, the Sigma 18-50mm shows little sign of colour creeping from the edges of our black test chart lines. The shorter you go, the more it appears, and at 18mm it’s very obvious. You can’t really expect perfect performance for this money, but it’s likely to be better than your supplied kit lens in any case.
From around 30mm to the longest end of the focal length range this lens is most impressive, with no sign of major distortion. At shorter focal lengths some barrel distortion does appear, but you’ll get that on any wide-angle lens. The distortion appears across the image and gets more pronounced as you move towards the edge of the frame.
Verdict The Sigma 18-50mm provides a constant aperture of f/2.8 for a price that allows the budget-conscious to consider an upgrade. The optic handles very well, and is compact in its design, plus it’s very lightweight too.
Specifications Filter diameter: 72mm
Weight: 450g
Dimensions (HxW): 79x85.8mm
Max. aperture: f/2.8
Min. aperture: f/22
Min. focus distance: 200mm
Lens hood: Yes
Image stabiliser: No
Format & fittings (FF=full-frame): APS-C; Canon, Nikon D, Sony, Pentax, Samsung, Sigma, FT