Pentax SMC-DA 21mm f/3.2 AL Limited - Review / Test Report - Analysis
Lens Reviews - Pentax

Distortion

The DA 21mm f/3.2 produces a relatively pronounced degree of barrel distortion (~2%) - this is not dramatic but a bit higher than expected/desirable for a newly designed fix-focal lens.

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

Vignetting

The DA 21mm f/3.2 is a dedicated APS-C lens and as such it tends to produce a comparatively higher degree of vignetting. At f/3.2 the problem is indeed more pronounced at 1.04EV. That's not too bad for a 21mm lens although not stellar either. The situation is already much better by f/4 and no longer field relevant by f/5.6.

MTF (resolution)

The DA 21mm f/3.2 Limited produced very good although not superb resolution results in the MTF lab. The center performance is already exceptionally high straight from f/3.2 whereas the border quality isn't quite as high. At f/3.2-f/4 the borders show good results but the real boost towards very good quality occurs at f/5.6-f/8. At f/11 there's a general decrease in quality due to the usual diffraction effects.

Please note that the difference between f/3.2 and f/4 is only a 2/3 aperture so the gain in quality isn't overly pronounced between these two settings.

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 fairly well controlled for a lens in this focal length class. The average CA pixel width at the image borders stays at and below 0.9px - this may be visible here and there but usually not to an annoying degree.

(Note: CAs can be reduced via imaging tools)




© by photozone.de