Tokina AT-X PRO FX SD 24-70 mm f/2.8 (IF)
8. Vignetting
| Canon 50D, 24 mm, f/2.8 | Canon 50D, 24 mm, f/4.0 |
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| Canon 50D, 45 mm, f/2.8 | Canon 50D, 45 mm, f/4.0 |
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| Canon 50D, 70 mm, f/2.8 | Canon 50D, 70 mm, f/4.0 |
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After looking at these thumbnails you know that no matter what focal length you employ, there is practically no vignetting at all. Our measurements confirm that effect. At every focal length at the maximum relative aperture we got exactly the same result that of 11% (−0.34 EV). On stopping down the aperture by 1 EV you make the vignetting decrease by 1% at the shortest focal length and by 4-5% by the longer focal lengths.
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Now let’s see how the situation changes when you attach the tested Tokina to the full frame EOS 5D Mark III.
| Canon 5D MkIII, 24 mm, f/2.8 | Canon 5D MkIII, 24 mm, f/4.0 |
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| Canon 5D MkIII, 45 mm, f/2.8 | Canon 5D MkIII, 45 mm, f/4.0 |
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| Canon 5D MkIII, 70 mm, f/2.8 | Canon 5D MkIII, 70 mm, f/4.0 |
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The most difficult combination of wide angle and f/2.8 aperture causes the loss of 55% (−2.29 EV) of light in the frame corners. It is a lot but not more than in the case of competitors. For the same combination of parameters both the Canon 24-70 mm II and the Tamron 24-70 mm VC lost over 60% of light. The Nikkor 24-70 mm VR performed better with a result of 46%.
Stopping down the aperture helps with the vignetting correction but to a degree which could hardly be called satisfactory. By f/4.0 that aberration reaches 38% (−1.37 EV), by f/5.6 it is 30% (−1.02 EV), and by f/8.0 it still gets to a still significant level of 29% (−1.00 EV). Further stopping down doesn’t provide any measureable effects…
A significantly better situation might be observed in the middle of the focal range - at the maximum relative aperture, we assessed the vignetting effect as 29% (−0.99 EV). On stopping down to f/4.0 that aberration decreases to 15% (−0.46 EV) and, what’s interesting, stops reacting to further stopping down.
At 70 mm the situation is worse once again but not so bad as at 24 mm. The brightness loss in the frame corners amounts to 47% (−1.85 EV) and it decreases to 29% (−0.98 EV) on stopping down the aperture to f/4.0. Employing f/5.6 relative aperture means 20% (−0.66 EV) of vignetting and its level decreases to 14% (−0.42 EV) on further stopping down to f/8.0. By f/11 the reduction of brightness in the corners amounts to 12% (−0.38 EV).
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