Viltrox AF 85 mm f/1.4 Pro
6. Distortion and field of view
Field of view
A rectilinear 85 mm lens should give you on full frame an angle of view of 28.56 degrees. In their official specification the producer of the Viltrox AF 85 mm f/1.4 Pro states that the offered angle of view is a bit lower, amounting to exactly 28 degrees. We decided to take a reality check. In order to do so we took photos of a starry sky and saved them as uncorrected 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 were able to measure the field very precisely, and exactly as it should be done, for rays of light coming from infinity. Our transformation was based on positions of 103 stars spread evenly across the frame. An average mesh-fitting error amounted to just 4 seconds of arc. Our final result amounted to 27.67 degrees with a measurement error on a level of 0.02 of a degree. It's even a tad lower than official specifications. It means the effective focal length of the tested lens is closer to 88 mm than declared 85 mm.Distortion
You don't expect any geometric deformations from a 85 mm lens and indeed, in case of the Viltrox AF 85 mm f/1.4 Pro there are no such problems, no matter what detector you employ. On the APS-C sensor we got a negligible value of +0.28% and on full frame the result was a tad higher, +0.58%. You can say with a lot of confidence that in this category the tested lens fares very well; of course you have to mention the fact that the Meike fared here even better.
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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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