With this new Sigma standard zoom for APS-C format, we take a step upwards from the variable aperture kit lenses. Kit lenses are undeniably excellent value when included in a kit, albeit it with restricted maximum apertures and sometimes somewhat unremarkable performance. The Sigma 18-50mm f/2.8 DC DN Contemporary lens offers instead a fast, bright and constant f/2.8 aperture and a promise of a higher level of technical performance. Let's couple the lens up with the 24MP Sony A5100 APS-C format body and take a close look at what it can do, and see whether it can justify moving up into a higher price bracket.

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Sigma 18-50mm f/2.8 DC DN Contemporary Handling and Features

Available in L-mount and E-mount, we have a nicely made dust and splash resistant lens that is basically just a tube in appearance. It weighs in at a svelte 290g, thanks to a construction comprising some aluminium (for rigidity) plus extensive use of Thermally Stable Composite. This TSC is basically a plastic composite material with a coefficient of expansion very close to aluminium, so the two materials can be used side by side. The L-mount version is compatible with Sigma's USB Dock UD-11.

There is a provided petal lens hood, solidly constructed, that fits cleanly and has absolutely no tendency to become detached in use. Within the bayonet fit for the hood is a conventional 55mm filter thread.

The wide zoom ring has an excellent grip. The lens extends when zoomed, and if we look into the front element as we zoom we can clearly see the baffle that changes the effective diameter of the lens optics. This keeps the lens at a constant aperture, as a 50mm f/2.8 lens requires a larger diameter of glass than an 18mm f/2.8. The front element has a fluorine coating to repel water, dust and grease. There are clear focal length markings at 18mm, 24mm, 28mm, 35mm and 50mm.

The focusing ring is electronic and operates slickly, just as we should expect. Focusing is down to 12.1cm (0.397 feet) at 18mm; a maximum magnification of 1:2.8. At 50mm, this becomes 30cm (0.984 feet) for a maximum magnification of 1:5. This is closer than average, which is always useful, increasing the versatility of the lens. All the usual Sony focusing options are selected via the camera menus, including AF-S, AF-C, AF-A, MF and DMF (Direct Manual Focus). DMF enables manual tweaking of the focus point whilst the camera is using AF. AF is driven by a stepping motor and this operates smoothly, quickly and virtually silently.

Optical construction comprises 13 elements in 10 groups, including 3 glass moulded aspherical and 1 SLD (Super Low Dispersion). The diaphragm has 7 rounded blades.

The bayonet mount is made of brass, a good choice for its durability and its smoothness of fit. Once clicked into place, there is no sign of any rotational movement and the fit is totally secure. There is the usual rubber seal around the rear of the lens to prevent water ingress, all parts of the dust and splash resistance.

The 18-50mm is designed to cover the APS-C crop format, which gives a “35mm equivalent” field of view of 27-75mm. This is a good standard range from wide-angle to short telephoto, the 50mm setting being ideal for portraits and close sports events. The wide-angle is not ultra-wide in today's perceptions but wide-angle enough to cover most images of groups of people, architecture and landscape. An excellent travel lens option, being light and enjoying that fast, bright f/2.8 aperture, and having totally hazard-free handling.