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Olympus M.ZUIKO 75mm f/1.8 ED - Review / Test Report - Analysis |
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Lens Reviews -
(Micro-)Four-Thirds
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Page 2 of 3
Distortion
Tele prime lenses tend to have marginal image distortion and this is also true for the Olympus lens - it produces just slight pincushion distortion of ~0.44%. This is also the original distortion as present in RAW files rather than an auto-corrected result.
Vignetting
Light falloff is typically auto-corrected on micro-four-thirds cameras. Consequently this is little to worry about at only 0.5EV fully open and it's negligible beyond. However, the RAW vignetting is quite a bit more noticeable at ~1.1EV at f/1.8. When stopping down just a tiny bit, the light falloff is not relevant anymore.
MTF (resolution)
The resolution characteristic of the M.Zuiko is outstanding straight from max. aperture down to f/4 and that's across the image frame. Diffraction has a limiting effect from f/5.6 onward but the quality is still very good at f/8. Overall these are best result that we have seen to date on a MFT camera.
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)
We have seen some extraordinary results in the resolution chapter and the goodness continues with marginal CAs (color shadows at hard contrast transitions at the image borders).
Bokeh
The quality of the bokeh (out-of-focus blur) is naturally a major aspect for such a lens and the Olympus doesn't disappoint us here. The transitions are very smooth and buttery and that's both in the foreground and background which is a rare characteristic.
Out-of-focus highlights are perfectly circular and evenly rendered from f/1.8 to f/2.8. However, at f/1.8 this applies only to the image center - in the border region you can see a slight deterioration towards a ellipsoid shape caused by vignetting. Starting at f/4 you can spot the individual aperture blades (just). However, this is comparatively 'late' thanks to the 9 aperture blades.
Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)
Bokeh fringing is a common issue with fast glass. It's visible as halos of different colors in out-of-focus areas - magenta (red + blue) in front of the focus point and green beyond.
The M.Zuiko 75mm f/1.8 shows noticeable bokeh fringing from f/1.8 to f/2.8 and still minor traces at f/4.
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