Olympus M.ZUIKO 17mm f/1.8 - Review / Test Report - Analysis
Lens Reviews -
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The M.Zuiko lens produces only a slight degree of barrel distortion (~0.5%) which is rarely noticeable in real life conditions. However, this is only a part of the story. Micro-4/3 images are auto-corrected according to the stored lens profile (lens firmware) - this is done either by the camera (JPEG) or by the more popular RAW-converters a la Photoshop. The "untouched RAW" results, showing the original capability of the lens, are much worse with a barrel distortion as extreme as ~4.5% so it is somewhat under-designed and relying on the auto-correction here.
The light falloff is comparatively heavy (1.1EV) at fully open aperture. Stopping down to f/2.2 reduces the issue quite a bit already but if you are shooting a scene where vignetting is disturbing you should stop down beyond f/2.8.
The resolution characteristic of the 17mm f/1.8 is decent although it stays short of its mighty cousin - the M.Zuiko 75mm f/1.8ED - which we reviewed recently here. Having said that, the center resolution is already very good to excellent at f/1.8 followed by good results in the outer image region. This is impressive at this setting. However, technically there's only a marginal improvement potential when stopping down. Diffraction has a limiting effect from f/5.6 onward but the results remain very usable even at f/8. For what it's worth we also verified the results based on uncorrected RAWs (without distortion correction) but it didn't really make much of a difference with respect to the borders. There is a slight degree of field curvature in the image corners which may be visible at large apertures.
The center quality of the tested sample was good for a lens in this class.
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
Chromatic Aberrations (CAs)
Lateral CAs (color shadows at hard contrast transitions at the image borders) aren't a really strong aspect of the Olmypus lens. An average CA pixel width of around 1.8px at the image borders will be visible in some situations.
In order to illustrate the issue - here's a sample crop taken from the image borders: