Fujifilm Fujinon XF 23 mm f/2.8 R WR
6. Distortion and field of view
Field of view
A rectilinear 23 mm lens on the APS-C/DX sensor should provide an angle of view amounting to 63.3 deg. In the official specification the producer states a bit higher value, that of 63.4 deg.Of course we decided to check the dimensions of this field in real life. In order to do so we took photos of a starry sky and saved them first as distortion uncorrected JPEG files and then as RAW files developed by neutral software. 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.
In case of analysed JPEG files our transformation was based on positions of 101 stars spread evenly across the frame. An average mesh-fitting error amounted to just 9 seconds of arc. In this case we reached an angle of 64.37 degrees with a measurement error on a level of 0.02 of a degree. This result is a bit higher than the official declarations of the producer but the difference is not high, not exceeding one degree.
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If you get uncorrected RAW files you can also check how wide field of view can offer you the optics of the new Fujinon. This time we used 112 stars for the transformation of coordinate systems and the average mesh-fitting error was higher, amounting to 25 seconds of arc. The field, reached by us, was also a tad wider, with a value of 65.36 deg and a measurement error is about 0.04 deg. Here you see an equivalent of a rectilinear focal length near 22 mm.
Distortion
When you apply JPEG files distortion correction is forced by the camera body. Small wonder this aberration is invisible in resulting photos. Officially it is just -0.19% so, within the margin of measuring error, practically in accordance with zero.Passing to RAW files the analysis shows us the real level of distortion of the tested lens. Here you deal with barrel deformations of -2.48%. With this angle of view I admit the result could have been better but the Fujinon should be defended a bit – it's hardly a bothersome level and the small, pancake-type construction always entails some compromises. Anyway the Sigma C 23 mm f/1.4 DC DN, a much bigger and optically more complex model, had here a slightly weaker result, that of -2.75%.
| Fujifilm X-T2, 23 mm, JPEG | |||
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| Fujifilm X-T2, 23 mm, RAW | |||
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