Pentax SMC-DA 50-200mm f/4-5.6 ED - Review / Test Report - Analysis
Lens Reviews - Pentax

Distortion

The DA 50-200mm exhibits only a slight degree of distortion throughout the zoom range. Rather typical for such lenses there is slight barrel distortion (~1.2%) at the wide end (50mm) and slight pincushion distortion at 100mm and 200mm.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
50mm 100mm 200mm

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

Vignetting

Typical for most dedicated APS-C lenses vignetting is quite pronounced at wide-open aperture and the problem can be visible at times (~1EV). It is no longer field relevant from about f/8 onwards.

MTF (resolution)

The resolution characteristic of the Pentax is highly varying and not convincing. At 50mm the center performance is very good to even excellent (f/8) but the border quality is dismal at wide-open aperture and not much better by f/5.6. From about f/8 the resolution is good. Usually I also provide the extreme border performance for the widest zoom setting but I spare you that (...). At 135mm the situation is quite a bit better with generally good to very good results. However, there's a performance drop at 200mm specifically at f/5.6. The center performance is good here whereas the borders are soft again. The situation improves at f/8 and more so at f/11.

Please note that the 1st tested lens has been replaced by Pentax and the 2nd tested lens has been reconfirmed by Pentax to be within specs. If you find all this to be surprising please feel free counter-check the findings with the real world sample images provided below (e.g. the "castle" or the "wall" image).

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)

Lateral Chromatic aberrations (color shadows at harsh contrast transitions) are quite well controlled at 135mm and also 200mm. At 50mm the CAs are a little more pronounced although still on an acceptable level.




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