Olympus M.Zuiko Digital 12-50 mm f/3.5-6.3 ED EZ review - Coma, astigmatism and bokeh

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Olympus M.Zuiko Digital 12-50 mm f/3.5-6.3 ED EZ

16 March 2012

Arkadiusz Olech

7. Coma, astigmatism and bokeh

The coma is quite unnoticeable in the centre of the focal lengths’ range, a bit higher at the maximum focal length and the highest at the widest angle of view but nowhere it reaches a high level. The correction of this aberration is more or less good.

Olympus M.Zuiko Digital 12-50 mm f/3.5-6.3 ED EZ - Coma, astigmatism and bokeh

When it comes to the astigmatism similar terms can be used as those describing the coma. It would be difficult to call it invisible because the average difference between horizontal and vertical MTF50 function values is 7.7%. On the other hand it would be difficult to complain about it because it is definitely not bothersome. Photos below show defocused images of a diode at 50 mm focal length which was positioned in the frame centre and in its corner. Those images are similar to each other even at the maximum relative aperture - a really praiseworthy performance.

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The heterogeneity of light layout in the form of clearly visible concentric rings are to the tested Olympus’s disadvantage though. After a strong stopping down the image of the diode doesn’t look very well because of the small number of diaphragm blades. Nowadays using apertures with 6-7 blades is the minimum standard of decency. The Olympus didn’t reach that minimum though – five blades are definitely not enough.