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Canon EF 28mm f/2.8 - Review / Test Report - Analysis |
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Lens Reviews -
Canon EOS (APS-C)
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Page 2 of 3
Distortions
The lens showed a slight to moderate degree of barrel distortions (~1%). Not stellar for
a fix-focal lens but still pretty decent in absolute terms.
The chart above has a real-world size of about 120x80cm.
Vignetting
On an APS-C DSLR the full frame EF 28mm f/2.8 enjoys the usual sweet spot
but the effect isn't all that pronounced regarding vignetting which is
relatively high at 0.8EV at max. aperture. However, from f/4 and up the issue
is quite negligible.
MTF (resolution)
The resolution figures in the lab where somewhat puzzling so I repeated the tests
several times in order to verify the findings. The center performance reaches its excellent
peak at max. aperture and deteriorates towards medium aperture - a highly unusual characteristic
which is unprecedented so far for a large aperture wide-angle lens. The border performance
behaves a little more conventional with good results at f/2.8 increasing to very good
figures at medium aperture settings. So despite the rather unusual MTF curve the performance
is on a pretty high level.
The resolution chart has been revised to take field curvature into account.
Below is a simplified summary of the formal MTF findings. The chart shows in line widths
per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to
know more about it you may check out the corresponding
Imatest Explanations.
Chromatic Aberrations (CAs)
CAs (visible as color shadows at harsh contrast transitions) can reach an average CA pixel width
of significantly more than 1 pixel at the image borders - a weak performance here especially
for a fix-focal lens. CAs can be reduced and usually even eliminated via imaging tools but such
a lens should definitely perform better than that.
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