Lens Test: Pentax-DA 17-70mm f/4 AL SDM AF

A very useful zoom lens that produced excellent SQF test results.

Pentax 17-70
Pentax 17-70

Pentax describes the 17-70mm f/4 lens as a “standard lens with extra zoom,” a cute catch phrase. But “standard zooms,” as they’re called, are one of the most popular lens groups. Using focal lengths from wide to tele really covers a lot of shooting, including scenery, snapshots and portraiture, making the standard zooms very useful.

This particular lens offers a 4.1X zoom range, a 26-107mm equivalent in full frame. It has two hybrid aspherical (AL) elements, which deter most chromatic aberration. Although the 17-70 is not a DA star lens (DA*), which is Pentax’s premium lens series, it has some of the premium features like the Pentax Super Protect (SP) lens coating to repel dust, moisture and grease. Seems well made, almost like a pro lens, not at all plastic-feeling, but, sorry, no special seals to keep out dust and moisture. It also has Pentax’s Supersonic Drive Motor (SDM),which the company claims makes for smoother and quieter autofocus operation. It’s the only no-DA* lens right now in Pentax’s lineup that has SDM. Unfortunately, in the lens that we tested, the SDM didn’t seem to be as quiet as Canon’s USM or Nikon’s SWM systems–we heard a low whiny sound as we autofocused.

In the optics department, our SQF tests found Excellent image sharpness and contrast at all three focal lengths. DxO Analyzer 3.2 tests showed Visible (0.45%) barrel distortion at 17mm, and Slight (0.17%) pincushion at 35- and 70mm, average results. The Sigma 17-70mm f/2.8-4.5, tested in our May 2006 issue, also had Visible barreling at 17mm, and Slight pincushioning at 70mm, but at 35mm it had Imperceptible pincushioning (0.03%), a significantly better result than the Pentax. Light falloff was gone by f/5 at 17mm, and f/5.6 at 70mm, there was no light falloff at 35mm, an above average performance very similar to the Sigma. At the close-focusing distance of 10.49 inches, maximum magnification ranged from 1:8.77 at 17mm to 1:2.92 at 70mm. This is considered an Excellent result. However, the Sigma did noticeably better at 70mm with 1:1.9.

An utilitarian lens which most Pentaxians will surely love, this lens did fairly well on all our tests. However, older Pentaxians beware: it has the new KAF3 mount and SDM, which means it will only autofocus on newer Pentax bodies. And it just could not equal the Sigma in all aspects of the lens competition.

VITAL STATISTICS

17-70mm (17.37-67.47mm tested), f/4 (3.56-3.98 tested), 17 elements in 12 groups. Focus ring turns 50 degrees. Zoom ring turns 90 degrees. Focal length marked at 17-, 24-, 35-, 50-, and 70mm.
•Diagonal view angle: 79-23 degrees
•Weight: 1.09 lbs.
•Filter size: 67mm
•Mounts: Pentax KAF3.
•Included: Lenshood.
•Street price: $480.

CERTIFIED TEST RESULTS

•Distortion: At 17mm, 0.45% (Visible) barrel. At 35mm, 0.17% (Slight) pincushion. At 70mm, 0.17% (Slight) pincushion.
•Light falloff: At 17mm, f/5. At 35mm, none. At 70mm, f/5.6.
•Close-focusing distance: 10.49 inches.
•Maximum magnification ratio: At 17mm, 1:8.77. At 35mm, 1:4.75. At 70mm, 1:2.92.

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