Pentax SMC DA 18-250mm f/3.5-6.3 ED AL (IF) review

Despite being described as an internal-focusing (IF) lens, the Pentax's focusing ring rotates when the camera is set to AF mode. This is a shame because, despite the ring's narrowness, it is nigh-on impossible to take a firm grip on the lens without obstructing its movement. Further disappointment comes from the jerky feel of the focusing ring when it is used in manual mode: it works well enough but it doesn't have the silky smoothness that Pentax users are likely to expect.

The broader zoom ring is a totally different sensation, offering just the right amount of resistance for easy operation. It has a boldly-ribbed rubberised grip and could, in theory, be rotated right across its zoom range in a single movement although smaller adjustments seem more likely.

As is normal for lenses of this type, a petal lens-hood is supplied and can be reversed for storage when not required. When stowed, the lens-hood obstructs the focusing ring (as well as the leading edge of the zoom ring) at short focal-length settings, and some users could be tempted to leave it at home for this very reason.

There is some chromatic aberration at both extreme ends of the zoom range, but this is not obtrusive in real-world pictures except in the case of demanding subjects such as architecture. In part, the fact that chromatic aberrations are visible is due to the zoom's high sharpness, which peaks at a very impressive 0.37 cycles-per-pixel. The 145mm setting is rather weak beyond f/11 but otherwise the lens is close-to or above the crucial 0.25 cycles-per-pixel level down to f/16 and remains solid for a further F-stop at 65mm and shorter focal-lengths.

The absence of image-stabilisation technology (coupled with having to clear the focusing ring) makes handholding the lens difficult at its longest focal-lengths and there is also some softness in the very corners of the image field. AF operation is no more than averagely quick.