Sony FE 85 mm f/1.4 GM review - Coma, astigmatism and bokeh

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Sony FE 85 mm f/1.4 GM

14 September 2016

Arkadiusz Olech

7. Coma, astigmatism and bokeh

The coma correction and the correction of other aberrations influencing the shape of point-like sources of light is not a strong point of the Sony FE 1.4/85 GM. Thumbnails below prove that at the maximum relative aperture the diode is slightly deformed already in the corner of the smaller APS-C sensor. In the corner of full frame the deformations are very distinct and the diode remains out of shape even on stopping down the aperture by 1 EV.

Center, f/1.4	Corner APS-C, f/1.4	Corner FF, f/1.4

Center, f/2.0	Corner APS-C, f/2.0	Corner FF, f/2.0

The starry sky proves to be even more ruthless for the tested lens when it comes to that category. Deformations of stars in the frame corners are clearly visible by f/1.4 and f/2.0. Even after employing f/2.8 you cannot get rid of that effect completely. It’s worth noticing that it is not entirely an astrophotography problem. Coma and other aberrations make the image resolution lower also in daylight photos.

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A7R II, JPEG, f/1.4, right bottom corner of the frame 1:1

Sony FE 85 mm f/1.4 GM - Coma, astigmatism and bokeh

A7R II, JPEG, f/2.0, right bottom corner of the frame 1:1

A7R II, JPEG, f/2.8, right bottom corner of the frame 1:1

The astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, is less pronounced than the coma. We determined its level as 8.5% - a moderate value.

The blur provided by the lens should only be praised. The circles don’t feature any noticeable local extreme points and the 11-blade aperture performs exceedingly well – it remains circular even on significant stopping down. Mechanical vignetting makes itself felt but only at the maximum relative aperture; by f/2.0 it is already moderate and by f/2.8 it disappears almost completely so the circles you see in the frame centre, on the edge of the APS-C and on the edge of full frame don’t differ widely.

Center, f/1.4	Corner APS-C, f/1.4	Corner FF, f/1.4

Center, f/2.0	Corner APS-C, f/2.0	Corner FF, f/2.0

Center, f/4.0	Corner APS-C, f/4.0	Corner FF, f/4.0