Viltrox AF 75 mm f/1.2
6. Distortion and field of view
Field of view
A rectilinear 75 mm lens on the APS-C/DX should provide an angle of view of 21.4 deg. The Fujifilm X system sensor is slightly smaller than the classic APS-C/DX so the official specifications of this lens feature also a slightly lower value of the field, amounting to 21.35 degrees.We decided to check the size of the field in reality. In order to do that 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. Our transformation was based on over 101 stars positioned evenly across the frame and average mesh-fitting error amounted to just 4 seconds of arc.
The field computed that way amounted to 21.2 deg, with the measuring error not exceeding 0.1 of a degree. It is a value only a tad lower than the value from official declarations and, with such a focal length of the lens, this difference simply doesn't matter.
Distortion
A telephoto lens with such an angle of view as offered by the tested Viltrox, shouldn't have practically any problems with geometric deformations on the edge of the frame. Indeed here the Viltrox performs as it should – its distortion remains practically unnoticeable. In case of JPEG files we measured a negligible value of +0.02% and RAW files showed a bit higher level, that of +0.05%. Mind you both results are in accordance with each other within the margin of measurement error and, at the same time, they are in accordance with zero. As you see the Viltrox AF 75 mm f/1.2 doesn't have any problems whatsoever in this category.
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| Fujifilm X-T2, 75 mm, JPEG | |||
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| Fujifilm X-T2, 75 mm, RAW | |||
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