As is often the case, the very fast lenses with extra-wide maximum apertures don't tend to be quite as sharp as the slower lenses.
This is amply demonstrated in our lab test results by the Canon, Nikon and Sigma 50mm f/1.4 lenses when compared with the Olympus and Pentax f/1.8 lenses in this group. The same holds true when comparing the Canon and Nikon 85mm f/1.8 lenses with the Sony f/2.8 lens.
Distortion isn't much of an issue with any of the lenses on test, but the Canon and Nikon 85mm are the most impressive, exhibiting practically no distortion at all. The Canon and Nikon 50mm lenses both have a little barrel distortion, and the Sigma 50mm has the most noticeable pincushion.
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Colour fringing is also very well controlled by almost all the lenses in this group test. The Olympus scores a little worse than most, however it's the Sony that is the least impressive.
Full of refinement, the Nikon 85mm f/1.8 boasts ring-type ultrasonic autofocus with smooth full-time manual override, and is our favourite portrait lens. It's sharp even at its largest aperture setting and sharpness is both very impressive and consistent throughout the rest of the aperture range, from corner to corner of the frame.
The provision of seven diaphragm blades is less than with the competing Canon lens, which also has slightly faster autofocus, but bokeh is beautiful.
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The Sony 85mm lens has very good overall image quality, apart from noticeable colour fringing, but it has a more basic feature set, build quality feels a bit flimsy and the maximum aperture of f/2.8 is somewhat less useful.
Moving down to the 50mm mark, which is often more ideal for general portraiture with cameras that have an APS-C format image sensor, quality is mixed. Neither the Canon nor Nikon lenses give very convincing sharpness at their maximum apertures of f/1.4, and the Nikon fails to improve much even at f/2.8. Even so, both lenses give a pleasant, dreamy look to portraits taken with wide apertures.
The Sigma 50mm gives greater sharpness at f/1.8 and is impressive at medium to narrow apertures, although there's a dip in sharpness at f/2.8. Overall, it's our 50mm portrait lens of choice.
The Olympus and Pentax lenses offer great sharpness, even wide-open, but they're expensive to buy, considering they have a reduced maximum aperture of f/1.8.