Pentax SMC-DA 16-45mm f/4 ED AL - Review / Test Report - Analysis
Lens Reviews - Pentax

Distortion

Typical for many standard zoom the Pentax lens produces a pronounced degree of barrel distortion at 16mm (~2.5%) changing to slight pincushion distortion when zooming towards 45mm (~0.7%). This is comparatively good for such a wide standard zoom.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
16mm 24mm 45mm

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

Vignetting

Standard-zoom lenses with a reduced image circle tend to vignette quite a bit specifically towards the wide end of the zoom range. This is also true for the Pentax SMC DA 16-45mm f/4 ED AL. At 16mm the vignetting is pronounced with ~1.2EV at f/4 but stopping down reduces the problem to a manageable degree. At 24mm and more so at 45mm the vignetting is well controlled for a lens in this class.

MTF (resolution)

The Pentax SMC-DA 16-45mm f/4 ED AL produced very good resolution figures in the MTF lab. At 16mm the center performance is superb straight from the max. aperture. The borders are good to very good. Stopping down improves the image contrast, less so the resolution on the focus plane (although the perceived sharpness improves due to the bigger depth-of-field). This behavior is also quite typical for the rest of the zoom range. The sweet spot of the lens is at 24mm where the center quality is excellent followed by very good borders. There's a slight drop in quality at 45mm which is most obvious in the image center whereas the border quality remains high. At f/11 diffraction affects the quality at all focal lengths.

A welcome aspect of the DA 16-45mm is its very flat focus field (low field curvature). As a resukt extreme borders have a lesser (later) tendency to loose focus compared to other standard zoom lenses.

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)

So far it looked good but the 16-45mm f/4 has also a dark soul - lateral chromatic aberrations (color shadows at harsh contrast transitions). At 16mm and 24mm CAs can be quite extreme with an average pixel width around 2.5px at the image borders. This is plain bad although the issue can be corrected via imaging tools thanks to its very symmetrical characteristic (see the 100% sample crop below). To be fair the CAs are of the less hostile blue-yellow type (rather than red-cyan). In sharp contrast to the wide end CAs are almost negligible at the 45mm setting.

Here's a illustration of the problem (@ 24mm f/8, upper left border, 100% crop):

Move your mouse pointer in/out of the image
for the uncorrected and corrected portion




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