The Pentax 12-24mm is designed specifically for DSLRs, notably the company’s K200D and K20D models. On these cameras it has an equivalent focal range of 18-36mm, and 18mm equivalent is very wide indeed. It will make a big difference when trying to take architectural or interior shots in confined spaces, or when shooting dramatic landscapes or creating perspective effects. In fact, while many SLR users go for a telephoto zoom as their first additional lens, a wide-angle zoom can prove just as useful.

But wide-angle zooms are difficult to make, and hence pretty expensive to buy. That certainly applies to this Pentax 12-24mm. It’s enough to make you consider a cheaper third-party Pentax-compatible alternative, like the Sigma 10-20mm. In fairness, though, equivalent

own-brand wide-angle zooms from Canon and Nikon cost even more, so maybe the Pentax isn’t such bad value after all.

It certainly feels well made, even if there is a slightly ‘plasticky’ feel to the exterior. The lens mount is metal, and there’s no slop or play in any of the controls. The zoom action is very smooth, and there’s no zoom ‘creep’ when the camera is held vertically. The focusing action is especially good. This too has a very smooth movement and quite a long travel, so it’s easy to focus precisely, not least because of the clearly marked distance scale. What’s more, you can focus manually even while the camera’s still in AF mode, simply by turning the ring.

The autofocus is slightly less impressive, because it relies on the somewhat noisy and occasionally hesitant AF motors in the camera body. Some Pentax lenses include their own AF motors, but this unfortunately doesn’t appear to be one of them, despite its hefty price tag.

This lens does have a slightly odd shape. It has a constant diameter right to the end, where it suddenly flares out to accommodate the large front element. It gets bigger still if you attach the petal-type lens hood supplied, which is a good idea because the exposed front element is prone to lens flare when you’re shooting into the sun. (If the sun is in the frame it won’t make any difference, but if it’s just outside the frame, it may prevent flare ‘spots’ and a general loss

of contrast.)

It’s a nice lens to use because it’s not too big or bulky for a lens of its type and the zoom and focus actions are so good. The only thing is, the optical performance is a little patchy.

Strangely, the lens did perform well in the static resolution tests, which produced excellent definition at all lens apertures and at all focal lengths. In fact, its consistency during these tests proved quite remarkable.

What the tests also revealed was some pretty strong chromatic aberration towards the edges of the frame. The resolution tests don’t necessarily pick up on this, but it is visible in the images. It’s even more apparent during everyday photography, where bright objects or areas away from the centre of the frame frequently display a purple/blue/yellow/green fringe. This is a little disappointing given that the lens includes special ED (extra-low dispersion) lens elements designed specifically to cut chromatic aberration. To an extent you’d expect aberrations to be more apparent in a lens as optically extreme as this one, but you might hope they’d be suppressed a little better than this.

It was also odd that in some of our real-world shooting the lens’s edge/corner performance was actually quite poor. Some lenses hold up quite well, until they get to within around 10% of the edge of the frame and then just let go, and we fear this might be one of them.

On the other hand, the levels of barrel distortion were surprisingly low. Barrel distortion is usually a big problem with wide-angle zooms and can compromise their usefulness for many types of shot, but the Pentax 12-24mm did pretty well in this respect.

In spite of the positives, this lens’s optical performance was just a little too inconsistent to give it a full thumbs up. It’s nicely made and handles well, and it will certainly expand the range and style of your photography. However, the colour fringing in particular could prove irritating, and you may find yourself spending too much of your time fixing it in your image editor. Not the sort of niggles you want, especially considering the price you’re paying.

Final Verdict The Pentax 12-24mm will dramatically widen your perspectives, but it’s pricey and there are some optical compromises. Issues with colour fringing and loss of edge definition mean more time spent in post-production 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.