Pentax SMC DA* 16-50mm f/2.8 ED [IF] SDM - Review / Test Report - Analysis
Lens Reviews - Pentax
Saturday, 08 November 2008 11:00
Article Index
Introduction
Analysis

Distortion

At 16mm the lens shows fairly heavy barrel distortion (~3.6%) - this is slightly higher than average for a standard zoom lens but then we're also talking about 16mm here rather than the usual 17mm or 18mm setting. Beyond the extreme wide-end the distortion is actually very well controlled with slight barrel distortion at 24mm and slight pincushion distortion 50mm.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
16mm 24mm 50mm

The chart above has a real-world size of about 120x80cm.

Vignetting

The Pentax lens is a dedicated APS-C lens and like most of its kind it shows a fairly pronounced degree of vignetting at large aperture settings. The weak spots are at 16mm @ f/2.8 (~1.2EV) and 50mm @ f/2.8 (~0.9EV). At all other tested settings vignetting is not really field relevant.

MTF (resolution)

The Pentax lens produced a roller-coaster ride in the resolution test-lab. At 16mm and 24mm the center performance is excellent, even superb whereas the border and corner performance is only fair at f/2.8, good at f/4 and very good from f/5.6 onwards. At 50mm @ f/2.8 the border quality drops to rather dismal levels although the center resolution stays on a very high level. Stopping down helps to recover the borders again. The global sweet-spot of the lens is reached around f/5.6.

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

CAs (color shadows at harsh contrast transitions) are the primary weakness of the Pentax lens. At 16mm @ f/2.8 the CAs peak beyond 2.5px on the average at the image borders. Stopping down improves the problem quite a bit without resolving it. At longer focal lengths the CAs could still be better at f/2.8 but beyond f/4 it is generally well controlled.

Verdict

It is difficult to find a final verdict for the Pentax SMC DA* 16-50mm f/2.8 ED [IF] SDM. On the one hand it has some obvious problems like a weak border performance at max. aperture and very pronounced lateral chromatic aberrations (CAs). On the other hand it is really very sharp and contrasty at medium aperture settings (f/5.6-8) and many users may actually forgive the border problems at f/2.8 because you either stop down for conventional photography or rely on the (very sharp) center for shallow depth-of-field situations (e.g. portraits) anyway. The build quality of the lens is also a step up from the consumer grade Pentax lenses and the silent (although not overly speedy) SDM is an extra bonus on top. The pricing of the Pentax 16-50mm f/2.8 is fair relative to its performance and build quality.

Optical Quality:    
Mechanical Quality:
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