Sigma AF 135-400mm f/4.5-5.6 APO Aspherical RF - Review / Test Report - Analysis
Lens Reviews -
Canon EOS (APS-C)
Wednesday, 26 December 2007 23:32
Page 2 of 3
Thanks to the rather moderate zoom ratio distortion is very well
controlled throughout the range. At 135mm the lens is free of distortion
and there's only a marginal increase in pincushion distortion towards
400m (0.24%). This is excellent for such a lens.
The chart above has a real-world size of about 120x80cm. Expect more distortion towards closer focus distances.
The Sigma is a full frame lens thus enjoying a sweet spot advantage on
APS-C DSLRs. Between 135mm to 300mm vignetting is not field relevant even
at wide-open aperture. At 400mm vignetting is a little higher but
still harmless in most situations. Stopping down a little helps to
reduce the issue to a negligible degree.
The Sigma AF 135-400mm f/4.5-5.6 APO is generally capable to provide very decent
resolution level. At 135mm both the center as well as the border quality is
very good even at wide-open aperture. At f/8 the lens was even able to pass
the excellent barrier in the center. There's a slight deterioration in quality
towards 300mm where the lens still manages to deliver very good results.
At 400mm @ f/5.6 the performance drops significantly - the lens delivers a rather soft
quality both in terms of resolution (slightly uneven) and contrast here.
However, stopping down to f/8 or f/11 lifts the quality significantly to
very decent levels again.
It is worth to mentioned that the lens was serviced twice by Sigma.
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
CAs (color shadows at harsh contrast transitions) are quite high at 135mm with a peak beyond
1.5px on the average at the image borders. At longer focal lengths the issue is relatively
well under control but still high compared to other lenses in this class.