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