Pentax SMC-DA 40mm f/2.8 Limited - Review / Test Report - Analysis
Lens Reviews - Pentax

Distortion

Typical for standard/normal lenses the Pentax DA 40mm exhibits only a minor degree of barrel distortion (~0.6%) - nothing to worry about under field conditions.

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

Vignetting

Regarding its APS-C image circle it doesn't really surprise that the DA 40mm f/2.8 produces a some vignetting at wide-open aperture (0.9EV). At f/4 the problem is already greatly reduced and it's negligible from f/4 onwards.

MTF (resolution)

Pancake lenses have the reputation to produce a very even resolution across the frame but at cost of peak performance. The Pentax DA 40mm f/2.8 Limited is indeed not as sharp as its direct cousins but frankly the difference is not really detectable by the naked eye. In the lab the lens was a already able to deliver very good results at f/2.8 and an excellent quality between f/4 and f/8. Typical for all lenses diffraction reduces the quality from f/11 onwards. The sweet spot is at 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)

Lateral chromatic aberrations (color shadows at harsh contrast transitions) are a non-issue of the Pentax. A rare but very welcome characteristic.




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