A standard zoom with macro functions...
When you bought your camera you probably also had a kit lens with it. Most of the lenses that come with SLRs are cheap and cheerful, and produce reasonable results. For many users, that’ll be the only lens they’ll ever use with the camera. Others, though, will want to expand the options – maybe with a wideangle zoom, maybe a good telephoto zoom, and sometimes replace the standard zoom with a higher-quality lens, perhaps one with macro capability?
That’s what Sigma hopes with its 17-70mm DC lens. This objective comes with built-in macro throughout the zoom range, offering close focusing down to 20cm, and a macro ratio of 1:2.3. It’s a DC lens, which in Sigma speak means it’s optimised for the APS-C sized sensor, so there’s a smaller imaging circle than the DG series, which is designed for full-frame 35mm sized sensors. The lens is constructed from 15 elements in 12 groups including an element made from Special Low Dispersion glass and two aspherical elements. The result is, says Sigma, a lens that provides excellent correction for a range of aberrations.
The DC moniker normally denotes a smaller lens than we’d expect for its focal range, and this is no exception. By dedicating the lens to a smaller sensor, the size of the glass is kept smaller, and certainly this particular optic is small and light. Yet despite that it is fast, with a maximum apeture of f/2.8 at the wide end and f/4.5 at the telephoto. The minimum aperture is f/22.
Similarly, as a DC lens, the build quality is not as rugged as the EX DG range, which is geared towards pros and semi-pros, but that doesn’t mean this model is a cheap and cheerful replacement. It’s constructed from metal and plastic, with a metal mount, and it should be able to take a few knocks. The focus and zoom rings are comfortable and quite secure, with a locking device to prevent the zoom slipping from 17mm when the lens is dangling from a camera strap. When using the lens to copy a set of coins, the zoom remained in place, showing that the stiffness of the zoom array is impervious to gravity, but it’s not so stiff as to prevent quick zooming in normal use.
I used the lens with a Nikon D50, and it worked snappily enough with that camera’s AF system, though not quick enough for really fast subjects. However, this is an indictment of the camera as much as the lens. Images are sharp, with crisp contrast and good colour. Whether I used the lens as a macro or as standard, I never had cause to complain about the results. I was concerned about vignetting when looking through the viewfinder, mainly from the petal-shaped lens hood at 17mm, but that was more to do with my eye’s viewing angle – there was no sign of this in the final images.
Whether you want to spend another £270 on a replacement standard zoom is up to you, but if you always want to try out a bit of macro too, this is a lens worth considering.