Meike 85 mm f/1.4 FF STM
6. Distortion and field of view
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 of the Meike 85 mm f/1.4 FF STM declare a value amounting to 28.9 deg. Our measurement kind of reconciles both of these versions as we got a result of 28.7 deg with the measurement error not exceeding 0.1 of a deg.It's worth adding that our measurement was made with a help of a photo of a starry sky. 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 for an uncorrected JPEG file was based on the locations of 81 stars spread evenly across the frame and the average mesh-fitting error amounted to just 6 seconds of arc.
Distortion
We don't expect that an 85 mm telephoto lens will have any problems with geometric deformations and indeed, in case of the Meike 85 mm f/1.4 FF STM there are no such problems, no matter what kind of detector you employ. On the APS-C sensor we got a negligible value of -0.10% and on full frame we have a result even closer to zero, amounting to just -0.02%. Both these values, within the margin of error, mean that the distortion of the Meike lens is practically zero. A round of applause!
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| Sony A7R IIIa, 85 mm, APS-C | |||
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| Sony A7R IIIa, 85 mm, FF | |||
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