Main Review

The gold ring around the front of its barrel tells you that this is a serious lens. Its f/2.8 maximum aperture is maintained right across the zoom range and although this results in a rather large lens it is very well balanced and therefore comfortable to hold and use. Cosmetically, however, it is a shame that the zoom action pushes the front element so far forwards (about 36mm) when the focusing mechanism is entirely internal.

The manual-focus ring is generous and has a throw of around 60°, which provides a rapid response but may be slightly too short for precise use at speed. The zoom ring is closer to the camera body and rather narrower: sadly, our review lens had a slightly jerky zoom action and the movement as a whole was rather stiff. Automatic focusing is very quiet but the lens' AF speed left a lot to be desired on the K200D review body.

Any attack from the elements shouldn't be a worry since Pentax DA* lenses are protected against inclement weather.

Image Quality
On paper this is a well-specified lens and the price reflects this, however its potential was not fully realised during testing.

Although the f/2.8 maximum aperture is useful for low-light and controlled depth-of-field photography, its use results in colour fringing at the edge of the frame, as well as comparatively poor sharpness figures with the exception of when it is fully stopped-down to f/22. On the other hand, closing down just one f-stop improves the recorded sharpness significantly. Distortion is well controlled and should never be a significant concern.

Also consider...
Within the DSLR sector Pentax shares the same lens mount as Samsung, which opens up additional options when it comes to choosing lenses. Samsung offers a 16-45mm f/4 and an 18-55mm f/3.5-5.6, both of which mirror lenses offered under the Pentax brand in terms of specification and price.

Turning to true third-party manufacturers, Sigma has a 17-70mm f/2.8-4.5 lens as well as an 18-50mm zoom that comes in a Pentax mount as both fixed-aperture (f/2.8) and variable-aperture (f/3.5 -5.6) versions.

Tamron offers a less expensive f/2.8 fixed-aperture zoom covering 17-50mm and there is also a 16-50mm f/2.8 zoom from Tokina.

Verdict

The most expensive of the Pentax lenses in this category 16-50mm did not always deliver everything that it promised. In particular, the f/2.8 aperture is more for bright viewing than it is for top-quality imaging. Similarly, the SDM system is indeed smooth and quiet but the lens was positively sluggish in comparison to other lower priced offerings in this range from Pentax.

Reviewer: Jon Tarrant