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Distortion
As with many other XF lenses, Fujifilm applies software correction to address the native distortion of the lens.
With this correction applied, there is literally no visible distortion in the images. When switched off (some RAW converters can do this, like Capture One for example), the small amount of native pincushion distortion becomes visible.
Vignetting
Just like distortion, vignetting is also automatically corrected. Even after the correction is applied, there is a fairly visible amount of corner darkening left at the largest aperture setting. Stopped down to f/5.6 and beyond, it is no longer noticeable.
The native, uncorrected vignetting is surprisingly high, reaching almost 2 stops at f/2.8.
Most users will likely rely on the automated vignetting correction and never notice the lens' high native vignetting. However, one should be aware of the drawbacks of software corrected vignetting (like increased corner noise).
MTF (resolution)
The lens delivers impressive resolution in the lab. The image center is excellent straight from the maximum aperture and stays on this high level until diffraction takes its toll at medium and small apertures.
The borders and corners reach very good performance straight from the maximum aperture and stay on this level down to f/11.
On the 26MP sensor the lens delivers slightly higher resolution in the image corners than on the image borders.
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)
The lateral CAs (color shadows at hard contrast transitions) are well controlled with values well below one pixel at large and medium aperture settings, increasing to around or just above one pixel stopped down to f/11 and beyond.
Bokeh
Background highlights are nicely rendered as evenly filled discs with a tad of outlining. Thanks to the 9 rounded aperture blades, the highlight discs retain their circular shape even when the lens is stopped down.
Due to mechanical vignetting, background highlights are rendered as cat's eyes towards the edges of the frame, especially at large apertures. The charts below give an impression of how highlights are deteriorated or slightly cut off at various aperture settings.
In real life images, this vignetting leads to 'swirly' bokeh especially at large apertures, as it can be seen in some of the sample images on the next page.
The Fujinon delivers a very smooth and pleasing image blur in background out of focus areas (to the left below), including the transition zone from in-focus to out-of-focus. Typical for most lenses, the image blur is less smooth with some double edges in the foreground (to the right below).
Bokeh Fringing / LoCA
Bokeh fringing (non-coinciding focal planes of the various colors, also referred to as longitudinal chromatic aberration, or LoCA for short) is an axial color fringing effect and a common issue with relatively fast glass. The halos typically have different colors - magenta (red + blue) in front of the focus point and green beyond. Unlike lateral CAs, bokeh fringing can not easily be fixed in post processing.
The XF 80 is not marketed as an APO lens, but still shows only a very small amount of bokeh fringing wide open. From f/4 onwards, hardly any fringing is noticeable.
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