Nikon Nikkor Z 50 mm f/1.4
6. Distortion and field of view
Field of view
A rectilinear 50 mm lens on a full frame sensor should provide you an angle of view of 46.8 deg but the producers in their official specifications state 47 deg. Of course we decided to check how big this field really is. In order to do so we took photos of starry sky and saved them as uncorrected JPEG files. Contrary to the Z 1.4/35 model the Nikkor Z 50 mm f/1.4 doesn't switch on automatic distortion correction and JPEG files can be devoid of distortion, vignetting and/or aberration correction.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 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. The transformation was based on the locations of 100 stars spread evenly across the frame and the average mesh-fitting error amounted to just 6 seconds of arc.
Our final result amounted to 46.60 deg with an error on a level of 0.03 deg. As you see the real field of view of the tested instrument is a tad narrower than the declared one but the difference is rather symbolic.
Distortion
In case of the smaller APS-C/DX sensor geometric deformations are practically imperceptible. Our official result is -0.23% so, in the limits of measurement effor, it brushes against zero.
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On full frame barrel distortion is a tad higher, reaching -0.48%, but still it's a low level, distinctly lower than the results of -1.5% or even -2%, typical for older constructions of double gauss.
It's also worth mentioning the fact that the distortion level, described above, was measured for a photo of our testing chart put in a distance of about 3 meters from the lens. In optical construction that are able to change their optical system with the change of the distance distortion often shows different values. Indeed such an effect can be observed also here. When you take photos from a minimum distance amounted here to 0.37 of a meter you have to take into account deformations of -1.75% and when you pass to infinity distortion decreases to just -0.24% so practically zero.
Nikon Z7, 50 mm, JPEG, APS-C/DX | |||
Nikon Z7, 50 mm, JPEG, FF | |||