Leica APO-Summicron-SL 75 mm f/2 ASPH.
6. Distortion and field of view
Field of view
A rectilinear 75 mm lens on full frame should provide an angle of view amounting to 32.18 deg. In the official specification the producer states a value of 31.8 deg. We decided to check the real values of field of view with the help of photos of a starry sky; we saved them first as corrected JPEG files and then as uncorrected RAW 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 of JPEG format files was based on positions of 101 stars spread evenly across the frame. An average mesh-fitting error amounted to just 13 seconds of arc. Our final result amounted to 31.77 degrees with a measurement error on a level of 0.06 of a degree. It's in perfect accordance with official specifications.
In case of uncorrected RAW files the transformation was based on positions of 120 stars and an average mesh-fitting error amounted to 12 seconds of arc. In this case the developped file has always a higher result which here amounted to as much as 31.84 degrees with a measurement error on a level of 0.05 of a degree. It is a level appropriate rather for a rectilinear full frame 76 mm lens but differences with official declarations are negligible.
Distortion
Minimum differences in fields of view we got for JPEG and RAW formats suggest that the tested lens shouldn't experience any problems with distortion correction. Especially that from such a focal length you shouldn't expect any problems in this area. Indeed, the results don't disappoint. In case of the JPEG file we got a result of -0.16%, and for the RAW file it is -0.11%. Both results are in accordance with each other within the margin of error and, practically, they amount to zero. It means you won't notice distortion in real life photos, not even a trace of it.
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| Panasonic S1R II, 75 mm, JPEG, FF | |||
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| Panasonic S1R II, 75 mm, RAW, FF | |||
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