The 16-45mm features a decidedly utilitarian design, with far more attention to functionality than aesthetics. It feels reasonably well-made, with construction quality very similar to, and perhaps a notch above, the 18-55mm kit lens (which for once is no bad thing). The lens mount is metal, and the body constructed from metal and high-grade plastics. The extra-wide zoom ring, with its deeply ribbed hard rubber grip, is especially welcome, and a decent manual focus ring with distance scale completes the package.   At a lightweight 365g, this is also a lens which you can easily carry on the camera all day long. However it’s not built quite up to the standards of Pentax’s high-end F2.8 SWM zooms, and is not weather sealed to match the K10D or K20D camera bodies.

The most unusual feature of this lens is its ‘reverse zoom’ design, meaning that it is shortest at 45mm telephoto and extends substantially to the 16mm wideangle position. This is rare in a lens of this class, and more usually found in professional-level F2.8 standard zooms. A practical impact is that this gives rise to some shadowing of the built-in flash at wideangle settings.

On the camera

The lens feels well-balanced on the K10D used for testing; the wide zoom ring provides a natural grip for the left hand, and the manual focus ring can be operated readily with just the forefinger. Overall it is a delight to use.


Autofocus is driven by a screw-drive system from the camera body, so AF speed, noise and accuracy is fundamentally dependant on the camera used. On our K10D test body, we found focusing to be generally fast and accurate under most conditions, although with a certain tendency to struggle a bit in low light. Here the faster than usual F4 maximum aperture at the telephoto end confers a noticeable advantage over the 18-55mm kit lens.

Lens body elements

The lens mount is the Pentax’s standard KAF, using a mixture of electronic and mechanical connections to interface with the camera.  To mount the lens, align the red dot with that on the camera body, and twist clockwise.

The black metal lever controls the aperture, and autofocus is driven from the camera body using a screw coupler; 6 complete turns are required to travel from infinity to closest focus.
The filter thread is 67mm, and does not rotate on focusing. This will be welcome to filter users, and demonstrates that someone at Pentax genuinely appears to understand photographers' needs.
The bayonet fitting, petal-type PH-RBL 67mm lens hood is supplied in the box, and mounts by lining up the white marks and twisting about 60 degrees, locking firmly in place. It’s solidly made of thick black plastic, and reverses neatly for storage. With its 92mm diameter, it should also fit happily in most bags.
The hood also features a slide-out ‘window’ for the easy operation of polarizing filters. This is a great idea, credit to Pentax for actually thinking about photographers needs, and not treating the hood as a superfluous extra like some other manufacturers.
The lens barrel has 13mm wide, deeply ridged sections directly next to the mount, to provide grip when removing or mounting the lens. Unfortunately, in what appears to be a triumph of marketing over engineering, the effect is somewhat spoiled by a smooth silver badge proudly proclaiming ’SMC Pentax DA’  placed bang in the middle of one of them. Doh!
The zoom ring rotates 80 degrees clockwise from wide to telephoto, with markings at 16, 20, 28, 35 and 40mm. The hard rubber grip is 38mm wide and deeply ribbed, and the zoom action smooth and precise.  Unusually for a zoom of this class, the lens is physically longest at wideangle, extending 32mm from the 45mm setting to 24mm. There is noticeable lateral ‘play’ of the lens barrel at full extension, which could have a negative effect on image quality.
The 9mm wide focus ring rotates 110 degrees anticlockwise from infinity to 0.28m. A distance scale is provided with markings in both feet and meters, but there’s no depth-of-field markings or infra-red correction mark. The ‘quick-shift’ manual focus system allows tweaking of the focus even when the camera switch is set to AF. The action is smooth and precise, making manual focus perfectly feasible. Very nice.

Reported aperture vs focal length

With its constant maximum aperture, the lens gives a maximum aperture of F4, and a minimum of F22, at all focal lengths.