The 18-55mm kit lens shipped as standard with most Pentax DSLRs is not one of the world’s greatest lenses. The zoom range is modest and the optical performance is a little below average, with soft-edge definition and a fair amount of chromatic aberration.

We’ve been looking at possible alternatives from the Pentax lens range and last month we tested the 17-70mm f4 and found it a useful improvement. There’s another option, though – the Pentax 16-50mm f2.8. This doesn’t have such a wide zoom range, but it makes up for it in other ways.

For a start it goes just a fraction ‘wider’, and the 16mm minimum equates to around 24-25mm on a 35mm camera. The main advantage of this lens, though, is that it has a constant f2.8 maximum aperture. Constant maximum apertures make manual exposure calculations easier (you no longer have to allow for a drop in maximum aperture at long focal lengths) and, the fast f2.8 speed of this lens, in conjunction with Pentax’s anti-shake system, makes this the perfect lens for low-light photography and portraits where you want to throw the background out of focus.

The resolution figures it produced in our tests are impressive. The definition at full aperture is lower, as you’d expect, but still not bad. It’s sharpening up considerably by f4, and by f5.6 its sharpness figures are very high. From there it tails off slowly towards the minimum aperture, but this is typical of any lens as the diffraction effects caused by small apertures start to take hold.

If there are any weak spots they’re at the extremes of the focal range, and at the edges of the frame. At 16mm, the lens is showing a little too much chromatic aberration for comfort, while at 50mm the definition at the edge of the frame at f2.8 is pretty soft. Overall, though, the performance is very good, and a fraction better than that of the 17-70mm we tested last month.

The difference in optical performance may be small, but there is a noticeable difference in handling and build quality. The 16-50mm does feel a more solid and weighty piece of kit, and while there is a slight tight spot in the zoom, the controls generally are very good. You get

full-time manual focus, too – even after the camera’s autofocus has locked on, you can still turn the Focus ring manually to fine-tune the setting.

The autofocus itself is a lot quieter on this lens, too – in fact it’s exceptionally quiet, to the extent that you feel it through your fingertips rather than hearing it. There is still some hesitancy in some conditions, but this is more likely to be a characteristic of the camera’s AF sensor rather than the lens.

The 16-50mm does have a shorter zoom range than the 17-70mm, and if you take more shots at longer range, that could be a problem. On the other hand, you’re getting a full stop increase in maximum aperture, and that can make a big difference to the light levels you can shoot in and the depth-of-field effects you can achieve.

It’s also worth pointing out that although the list price of the 16-50mm is considerably higher, the street prices are often a great deal closer. With that in mind, this is perhaps the most desirable of all the Pentax standard zooms.

Final Verdict The 16-50mm is a full stop faster and a fraction sharper than the 17-70mm we tested last month. However, it feels noticeably more substantial in terms of handling and build quality, with a solid, weighty feel and impressive controls OVERALL

Our lens reviewer, and technical expert, Rod is a veritable photographic encyclopaedia. His illustrious CV has seen him write for many mags, websites and journals.