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Tokina AF 28-70mm f/2.8-2.6 AT-X Pro II - Review / Lab Test Report - Analysis |
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Lens Reviews -
Canon EOS (APS-C)
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Page 2 of 2
Distortion
The lens shows a medium degree of barrel distortion at 28mm changing
to marginal barrel distortion at 40mm and slight pincushion distortion
70mm.
28mm:
40mm:
70mm:
Vignetting
The AF 28-70mm f/2.6-2.8 AT-X Pro II is a full frame lens so it can take advantage
of a sweet spot effect on APS-C DSLRs. Vignetting is no major issue in all but the
most critical situations even at wide-open aperture.
MTF (resolution)
The Tokina exhibited very good resolution figures under lab conditions.
At 28mm the center resolution is excellent straight from the max. aperture
setting. The border quality isn't quite as high but still on a good to
very-good level.
At 40mm the center quality remains on a very high level and the borders catch
up significantly with excellent figures from f/5.6 and up.
There's a slight performance drop at 70mm specifically at f/2.8 where both the center
as well as the border quality is very good. The local performance peak
is at f/5.6 where both the center as well as the borders are excellent again.
The tested sample exhibited an off-coplanar projection (centering defect).
According to Christian (owner) the lens is quite soft at very close focus
distances at 70mm which may be a side effect of the defect.
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
Chromatic aberrations (color shadows at harsh contrast transitions) vary
quite a bit according to the chosen focal length. At 28mm the problem
correlates to the chosen aperture - at f/2.8 the issue is marginal
but it increases to quite critical levels at medium aperture settings
with a max. of 1.87 pixel on the average at the image borders.
At 40mm and more so at 70mm the issue is quite a bit less pronounced.
Verdict
The Tokina AF 28-70mm f/2.6-2.8 AT-X Pro II was indeed able to beat
the performance figures of its successor - the AF 28-70mm f/2.8 AT-X Pro SV.
Probably not really surprising because the lens was also quite a bit more
expensive at the time. Generally the lens produced pretty impressive
results specifically regarding resolution. The level of distortions
is quite moderate for such a lens and the vignetting figures are very
low. On the other hand CAs can reach a disturbing level at 28mm at medium
aperture settings. The build quality of the lens is, in principal, exceptional
and as good as the very best genuine brand products here. Unfortunately
the imperfect AF/MF switch mechanism doesn't really fit into the otherwise
brilliant mechanical implementation.
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