Lens Test: Pentax-DA 18-135mm f/3.5-5.6 DC WR

With the widest zoom range of any current Pentax lens (7.5X), the new 18–135mm f/3.5–5.6 ($500, street) is the closest it has today to an all-in-one zoom. A 27–202.5mm full-frame equivalent, this is also one of the few lenses in its class with a weather-resistant (WR) O-ring on the lensmount. Other perks: A quiet DC AF motor and seamless shifting between manual and autofocus.

At less than 3 inches long (contracted), this is by far the smallest in its class of four (tested) comparable zooms. It throws a small shadow when used with an on-board flash at the closest focusing distances and widest focal lengths. Its smooth-turning manual-focus ring sits conveniently close to the mount—unlike other current Pentax zooms, all of which place the MF ring out past the zoom collar, often at the outer barrel rim. Manual-focus fans will like the change. The generous zoom ring, though free of creep, turns slightly stiffly.

Pentax produces some of the noisier AF motors today, so the near-silent DC focusing mechanism in this lens is a welcome addition. The AF is a pleasure to use; its speed and accuracy (on the K-7) impressed us.

In our optical bench tests, the lens produced Excellent-range SQF numbers at the tested focal lengths­—a promise of superlative sharpness and contrast. Its performance closely matched those of the comparable Canon, Nikon, and Tokina zooms, but at the aperture-range extremes, was slightly softer than the Sigma 18–125mm.

Its distortion control was more robust at the wider focal lengths than that of the competition, though it still allowed Visible-range barreling (0.47%). Likewise, its top subject magnification of 1:3.34 at 135mm was also best in class. Conversely, however, its light falloff was slightly below average. (Full test results are at left.)

On the whole, this lens is a worthy choice, with more than its share of compelling talents. Sharp, weather-resistant, compact, and quiet-focusing, it also boasts a zoom range suitable to most subjects.

Still, all-in-one zoom fans won’t find it replaces Pentax’s discontinued 18–250mm. They’re waiting for something like the Tamron 18–270mm, and it wouldn’t surprise us if Pentax eventually delivered one.

SPECIFICATIONS
18–135mm (17.99–134.98mm tested), f/3.5–5.6 (f/3.45–5.76 tested), 13 elements in 11 groups. Focus ring turns 80°. Zoom ring turns 80°. Focal lengths marked at 18-, 24-, 35-, 50-, -70, 100, and 135mm.
Diagonal view angle: 76–11 degrees.
Weight: 0.98 lb. Filter size: 62mm.
Mount: Pentax KAF. Included: Hood. Street price: $500.

TEST RESULTS
Distortion: At 18mm, 0.47% (Visible) barrel. At 70mm, 0.26% (Slight) pincushion. At 135mm, 0.21% (Slight) pincushion.
Light falloff: At 18mm, gone by f/5. At 70mm, gone by f/5.6. At 135mm, gone by f/6.3.
Close-focusing distance: 11.78 in.
Max. magnification: At 18mm, 1:10.18. At 70mm, 1:3.70. At 135mm, 1:3.34