Viltrox AF 55 mm f/1.8 EVO
6. Distortion and field of view
Field of view
A rectilinear 55 mm lens on a full frame sensor should provide you an angle of view of 42.9 deg and the producers of the Viltrox AF 55 mm f/1.8 EVO in their official specifications state the value of 43 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 127 stars spread evenly across the frame. An average mesh-fitting error amounted to just 12 seconds of arc.We got a result of 44.14 deg with a measuring error of 0.03 deg, so a tad higher than stated in specifications and higher than the focal length value itself might suggest. The differences are slight and mean that the angle of view is an equivalent of a distortion-free focal length of 53.4 mm.
Distortion
When the Viltrox 1.8/55 EVO is attached to a camera with the smaller APS-C/DX sensor, its geometric deformations are imperceptible – our measurements showed a level of -0.07% and it is, within the margin of error, in accordance with zero.
After passing to full frame the increase of this aberration is slight, with a result of just -0.12%. Once again, within the margin of measurement error, you can speak about zero. The Viltrox AF 55 mm f/1.8 EVO deals with distortion in a splendid way.
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Direct rivals, mentioned in this material, also performed very well, perhaps apart from the Sonnar. Still, the official results of the Viltrox are here the lowest – once again, a round of applause!
| Sony A7R IIIa, 55 mm, APS-C/DX | |||
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| Sony A7R IIIa, 55 mm, FF | |||
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