Pentax SMC-DA* 50-135mm f/2.8 ED [IF] SDM - Review / Test Report - Analysis
Lens Reviews - Pentax

Distortion

The DA* 50-135mm produces a moderate degree (~1.2%) of barrel distortion at 50mm changing to moderate pincushion distortion (~1.1%) when zooming out to 135mm.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
50mm 90mm 135mm

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

Vignetting

Typical for most dedicated APS-C lenses the vignetting is more pronounced at wide-open aperture and the problem can be visible at f/2.8 at longer focal lengths. At f/4 the vignetting is usually not field relevant anymore and from f/5.6 onwards it's a rather negligible issue.

MTF (resolution)

This is the 2nd tested sample of the DA* 50-135mm f/2.8. The first sample was very sub-standard and the test report had to be canceled accordingly. This 2nd sample performed much better although it is still not 100% perfect at 135mm.

At 50mm the center resolution is excellent straight from wide-open aperture and the border quality is generally very good with an excellent peak at f/5.6. Even the extreme corners remain on a very high level. At 90mm and 135mm there's a performance drop at f/2.8 - less so in the center of the image field but the borders suffer somewhat resulting in only "good" figures. There's a quality boost at f/4 and the peak is reached at f/5.6 with an impressively high resolution across the frame.

Based on real world use I'd say that the performance of the lens deteriorates towards close focus distances so better keep a distance of 1.5m+ (specifically combined with a 135mm setting). The quality of the otherwise very fine bokeh (out of focus blur) is also affected here.

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)

Similar to its Tokina cousin the Pentax DA* 50-135mm f/2.8 suffers somewhat from high chromatic aberrations (color shadows at harsh contrast transitions) at the extreme ends of the zoom range. An average CA pixel width around 1.3px at the image borders is not a disaster but it can be visible in some situations. Please note that CAs can be significantly reduced via imaging tools (e.g. Photoshop CS2 or CS3).

Purple fringing seems relatively minimal. If pushed to the extremes you can produce Longitudinal Chromatic Aberrations (tinted focus halos) but during normal use this seems to be a non-issue.




© by photozone.de