Viltrox AF 35 mm f/1.2 LAB
6. Distortion and field of view
Field of view
A rectilinear 35 mm lens should give you, on full frame, an angle of view of 63.4 degrees. In their official specification, the producer of the Viltrox AF 35 mm f/1.2 LAB states that the offered angle of view is a bit higher, amounting to 64.2 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 199 stars spread evenly across the frame. An average mesh-fitting error amounted to 2 minutes and 18 seconds of arc.The result, reached by us, amounted to 64.52 deg with a measurement error on a level of 0.07 of a degree. It's even a tad higher than stated in official specifications and, at the same time, a tad higher than the focal length value suggests. Still, the differences are merely cosmetic, meaning that the resulting angle of view is equivalent to the distortion-free focal length of 34.3 mm.
Distortion
A contemporary and optically complex 35 mm lens should correct distortion very well. The fact that the Viltrox AF 35 mm f/1.2 LAB is an exception to this rule is backed by the result on the smaller APS-C/DX, with barrel distortion of -1.32%. The level is perhaps not high, but I've handled many 35 mm instruments that showed a lower level of this aberration even on full frame.
As we've already mentioned full frame, the distortion level of the tested Viltrox amounts to -1.05%, so officially it is lower than on the APS-C/DX sensor. A paradox? Not really. The producers have got this result by introducing quite nasty moustache distortion. I honestly don't remind myself of another 35 mm lens with such a high level of deformations of this type. If you measure distortion within the 1:1 markings area you see that these 'moustache' are big indeed, with barrel distortion reaching -2.15%.
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A big, optically complex 1.2/35 lens really could have performed better, with good distortion correction and without significant moustache deformations. It's a pity the optics constructors of the Viltrox have taken a shortcut.
| Sony A7R IIIa, 35 mm, APS-C | |||
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| Sony A7R IIIa, 35 mm, FF | |||
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