Sony FE 85 mm f/1.4 GM II review

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Sony FE 85 mm f/1.4 GM II

9 September 2024

Maciej Latałło

6. Distortion and field of view

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Field of view

A rectilinear lens, devoid of distortion, with a focal length of 85 mm should provide you a field of view of 28.5 degrees on full frame. In official specifications the producers declare a tak higher value, amounting to 29 deg. It might suggest that the real focal length of the Sony 1.4/85 GM II might be a tad shorter. We decided to take a reality check. In order to do that we took photos of starry sky and saved them as JPEG files. Then we transformed the pixel layout (X,Y) from the photo into the equatorial coordinate system (right ascension and declination), which locates a star on a celestial sphere. That way we could determine the field of view of the lens with utter precision and in the right way, so for rays of light coming from infinity. The transformation was based on the locations of 121 stars spread evenly across the frame and the average mesh-fitting error amounted to just 6 seconds of arc.

Finally we got a result of 29.18 deg with an error not exceeding 0.1 of a degree. As you see the real field of the tested instrument is a tad wider than the declared one and it corresponds to a focal length of about 83 mm.

Distortion

We don't expect that an 85 mm telephoto lens will have any problems with geometric deformations and indeed, the Sony FE 85 mm f/1.4 GM II doesn't show any trace of such problems, no matter what detector you use. On the APS-C sensor we got a result amounting practically to zero, officially reaching +0.13%, and on full frame it was a tad higher, but still not especially bothersome, amounting to +0.45%.