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Tokina AF 12-24mm f/4 AT-X Pro DX (Nikon) - Review / Test Report - Analysis |
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Lens Reviews -
Nikon / Nikkor (APS-C)
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Page 2 of 3
Distortion
At about ~2.3% the lens shows a quite pronounced degree of wavy barrel distortion
at 12mm decreasing continuously towards the long end of the zoom range (0.2%).
It's quite interesting to note that the distortion seem to grow exponentially
compared to the Canon variant (1.5x vs 1.6x crop factor).
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Move the mouse cursor over the focal length text marks below to observe the respective distortion
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| 12mm |
18mm |
24mm |
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The chart above has a real-world size of about 120x80cm.
Vignetting
At 12mm @ f/4 the lens shows very noticeable vignetting (~1.4EV) which will be visible in most scenes.
At f/5.6 the problem is already largely reduced (~0.78EV) but stopping down a little further may
be a good idea if required. At 18mm and 24mm vignetting is far less pronounced
even at wide-open aperture. One stop down vignetting is already quite negligible here.
Similar to the distortion characteristic vignetting is again more intense on the D200 (1.5x crop) vs the EOS 350D (1.6x).
MTF (resolution)
The Tokina showed very impressive resolution figures in the MTF lab. Unlike many other lenses with a
reduced image circle it was capable to combine a generally excellent center performance with very good
borders and still very good extreme corners. The center performance decreases marginally towards the
long end whereas the borders improve slightly.
If anything the rather significant drop in quality at 12mm f/11 may be worth a critical comment but
then you rarely need to stop down beyond this setting due to the already extreme depth-of-field
at this focal length. The field curvature is quite moderate.
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)
CAs (color shadows at harsh contrast transitions) are the primary weakness of the Tokina.
At 12mm and 18mm CAs peak way beyond 2px on the average at the image borders.
Stopping down helps to reduce the problem but it's still fairly high at f/8.
At 24mm the situation eases somewhat.
Please note that CAs are no principal show-stopper because they can easily be corrected
via various tools such as the Adobe Photoshop RAW converter or Debarrelizer (a Photoshop plug-in).
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