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Pentax SMC-FA 35mm f/2 AL - Review / Test Report - Analysis |
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Lens Reviews -
Pentax
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Page 2 of 3
Distortion
The FA 35mm f/2 AL exhibits only a minor degree of barrel distortion (~0.85%) - this is
usually nothing to worry about in field conditions.
The chart above has a real-world size of about 120x80cm.
Vignetting
As a full format lens the FA 35mm f/2 benefits from the usual sweet spot effect
on APS-C DSLRs. At f/2 the level of vignetting is already fairly moderate (0.66EV)
and negligible from f/2.8 onwards.
MTF (resolution)
The first tested sample of the lens had a centering defect which spoiled the
results quite a bit. However, a re-test with a 2nd sample showed the full
potential of the lens. At f/2 the lens is already capable to deliver a very
good performance across the frame. Stopping down increases the resolution
even further till an outstanding maximum is reached around f/4. At f/8
there're marginal diffraction effects but the quality remains easily on an
excellent level.
Please note that the MTF results are not directly comparable across the different systems!
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 very low
at f/2 and the problem does only increase slightly towards smaller
apertures. Even at its peak (f/8) the CAs are only on a medium level with an average
width of ~1.2px at the image borders.
Typical for many ultra-large aperture lenses you can experience some purple fringing
in extreme contrast conditions at wide-open aperture. Here's an example (100% border crop
of a water fountain image):
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