Curvilinear distortion
It may well be true that curvilinear distortion is less noticeable in
real-world images than lab images, but good control of this is still
desirable in a lens because it is flattering for portraits and less
distracting in uniform patterns such as brickwork, which would otherwise
be warped.
None of the lenses here suffers badly from curvilinear distortion,
but differences can be seen between them when viewing the results from
our lab – as seen in the bowing of lines in our graphs.
Generally,
each lens shows minor barrel distortion at 70mm, and by the mid 135mm
setting it has shifted to pincushion distortion, which is again almost
negligible. Pincushion becomes more pronounced at the 200mm setting, but
is not a concern.
A direct comparison shows that the Tamron and
Nikon lenses have the best control over barrel distortion at 70mm, while
the Sony, Tamron and Canon lenses are least affected by pincushion
distortion at 200mm. None of the lenses is distorted beyond
approximately 0.6% at any focal length.
Image: The bowing of lines in these charts indicates curvilinear
distortion. All five lenses control this distortion very well, and the
most extreme it gets is at 200mm, where pincushion distortion is more
pronounced. Even then, one will struggle to see the effect in most
‘real-world’ images:
Chromatic aberration
Each lens has a complex construction, containing elements (be it ED, SLD or fluorite) that reduce distortions such as chromatic aberration. In the centre of the frame at any focal length it is difficult to find chromatic aberration in any lens, although in the bike picture there are traces in each lens.
It appears more pronounced in the Canon and Nikon lenses, but this is in part due to the slightly greater contrast and sharp edges than, say, the Sigma lens. The Tamon lens controls the distortion particularly well. At 135mm, this distortion is under control.
In short, chromatic aberration is another type of distortion that is well controlled by all the lenses and is certainly something that can be dealt with quickly post-capture.
Images: Chromatic aberration is, on the whole, well controlled in each
lens and certainly something that can be dealt with post-capture. In
this scene, taken at 70mm and f/2.8, the Tamron lens shows the best
control
Vignetting
A slight surprise is that the Sigma lens has just as good control over vignetting than the Canon lens when used at 70mm and f/2.8. The Tamron lens appears the most affected, while the Sony and Nikon versions show better control.
Used in the APS-C format, vignetting is of no concern at any setting, because only the unaffected central portion of the frame is used in an image.
Image: Vignetting is evident in all five lenses at f/2.8, reduced by the f/4 setting and all but gone with the camera set to f/5.6 aperture or smaller
