Pentax-DA 18-270mm F3.5-6.3 Review

Autofocus

The SMC Pentax-DA 18-270 mm F3.5-6.3 ED SDM super zoom has a built-in autofocus motor (Pentax calls it SDM - Supersonic Drive Motor) and no provision for autofocus driven by the motor in the camera body (the lens has no screwdrive mechanism).

Its autofocus is silent and generally accurate. In daylight it is plenty fast for most types of shooting but we would not consider it the ideal lens for sports photography since we had some problems with tracking a fast moving object with our K-5. In daylight there was no hunting.  We have not tested this lens with DSLRs older than the K-5, but we can only assume that on cameras such as the K20D or K-x, it will have a harder time focusing properly at the long end, and even outdoors.

Indoors in poor light the K-5 and K-30 struggle with this lens at the long end (135mm and beyond) where the max. aperture drops to F6.3. The lens occasionally refuses to lock on - it doesn't hunt, it just sits there refusing to focus. The results were better on a K-5 II with its upgraded autofocus module; on the newer body, the lens was able to lock on just about anything (though it would still take several seconds to lock on).

We found that the distance scale indicates but a rough approximation of the distance to the subject. The value shown varies with on the focal length even with a stationary camera. It is particularly off at 18mm, often indicating a distance beyond infinity when the subject is but five to seven meters away. We'd rather not have a distance scale than something like this.

Contrast Detect AF (Live View)

In Live View, the 18-250mm focuses very slowly when zoomed in, and indoors it will sometimes fail to lock focus, or will lock focus incorrectly.  We therefore don't recommend this lens for K-01 users and those who like using live view.  Below is a live view demonstration using the Pentax K-5 IIs:


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