Olympus M.Zuiko Digital 25 mm f/1.8 review - Coma, astigmatism and bokeh

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Olympus M.Zuiko Digital 25 mm f/1.8

30 April 2014

Arkadiusz Olech

7. Coma, astigmatism and bokeh

The performance of the coma is quite interesting. At the maximum relative aperture it is clearly visible but when you stop down to near f/2.5 it disappears practically completely.

Olympus M.Zuiko Digital 25 mm f/1.8 - Coma, astigmatism and bokeh

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Still the astigmatism remains the biggest problem of the tested lens; it is also the main reason why the Olympus cannot break any resolution records. Please, check the difference between vertical and horizontal MTFs for one of our testing charts.

By f/1.8- 2.8 the average difference between vertical and horizontal MTF function values exceeds a high level of 20%. Only by f/4.0 the astigmatism decreases to a moderate level of 9% and by f/5.6 it drops further to a low value of 5%.

The appearance of defocused images is beyond reproach. Out of focus light points still feature a bit of concentric rings but their intensity is low and the rings themselves come without any distinct rims on the edge.