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Tokina AF 28-70mm f/2.8 AT-X Pro SV - Review / 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 some quite pronounced barrel distortion at 28mm changing
to slight pincushion distortion at 40mm and 70mm.
28mm:
40mm:
70mm:
As usual you should probably expect more distortion towards closer focus distances.
Vignetting
The AF 28-70mm f/2.8 AT-X Pro SV is a full frame lens so it can take advantage
of a sweet spot effect on APS-C DSLRs. Vignetting is almost no
issue except maybe at 70mm @ f/2.8 where it may be noticeable in extremely critical
scenes. A very good performance here for a standard zoom.
MTF (resolution)
The Tokina exhibited a good but mixed performance under lab conditions.
At 28mm the lens was capable to produce very good to excellent results
throughout the tested aperture range.
At 40mm the corner performance suffered substantially at wide-open
aperture whereas the center quality remains on a very high level.
At f/4 the corners catch up to good lenses increasing further till
f/8 with very good results again.
At 70mm the lens is quite soft at wide-open aperture with pretty bad
corners. The quality increases gradually towards medium aperture
settings peaking at f/8 in excellent resolution figures even including
the corners.
It is worth to mention that the lens suffered from a slight centering
defect at 28mm.
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
is most pronounced exceeding an average CA pixel width of 1.5 pixels at
the image corners at and beyond f/5.6. At 40mm and more so at 70mm the
issue is quite a bit
less pronounced.
Verdict
The Tokina AF 28-70mm f/2.8 AT-X Pro SV is Tokina's budget offering in
this lens class and it comes with a few compromises specifically with
an imperfect focus-clutch mechanism (AF/MF switch) and a quite soft
performance at 40mm and 70mm at f/2.8. However, the optical quality
is high to very high at all other settings (f/4 & up and at 28mm)
and the principal build quality is very high.
A common question regarding all classic 28-XXmm zooms is the usefulness
of APS-C DSLR. With a field-of-view equivalent to 45-112mm these
zooms can be more classified as portrait lenses rather than standard zooms
which is probably not all that attractive anymore for most users.
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