Viltrox AF 35 mm f/1.8 EVO
6. Distortion and field of view
Field of view
A rectilinear 35 mm lens on a full frame sensor should provide you an angle of view of 63.4 deg and the producers of the Viltrox AF 35 mm f/1.8 EVO in their official specifications state the value of 63 deg exactly. Of course we decided to check how big this field really is anyway. 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 201 stars spread evenly across the frame. An average mesh-fitting error amounted to 1 minute and 6 seconds of arc.Our result amounts to 61.96 deg with a measurement error on a level of 0.08 of a degree. It's a tad lower than stated in official specifications and suggested by the focal length value, but the differences are slight. It seems the resulting angle of view is the equivalent of the distortion-free 36 mm focal length.
Distortion
When the Viltrox 1.8/35 EVO is attached to a camera with the smaller APS-C/DX sensor, its geometric deformations are quite innocuous – our measurements showed a slight barrel distortion of -0.89%.
After passing to full frame, the increase of this aberration is slight, with a result of just -1.06%. Still, a small level of moustache distortion helped here a bit. As a result, when you limit your measurements to the 1:1 area, barrel distortion increases to -1.98%.
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Overall, taking into account the parameters of the tested lens, its performance in this category is sensible, without any serious reasons to complain. Of course you can mention the fact that the rival Nikkor and Sony models fared in this category a tad better, without introducing moustache distortion.
| Sony A7R IIIa, 35 mm, APS-C | |||
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| Sony A7R IIIa, 35 mm, FF | |||
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