Panasonic Lumix S 85 mm f/1.8
6. Distortion and field of view
Field of view
A rectilinear 85 mm lens on full frame should provide an angle of view amounting to 28.56 deg. In the official specification the producer states a value of 29 deg.We decided to measure the real values of the field of view. We took photos of a starry sky and 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 4 seconds of arc. In this case we reached an angle of 28.82 degrees with a measurement error on a level of 0.07 of a degree. In other words our result was in perfect accordance with the official specification.
In case of uncorrected RAW files the transformation was based on positions of 113 stars and an average mesh-fitting error increased to 10 seconds of arc. In this case the developed file always features a tad higher physical resolution so our result amounted to slightly more, 28.89 degrees, with a measurement error on a level of 0.07 of a degree.
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No surprises in this place – the lens offers you exactly as much as it is supposed to do.
Distortion
When it comes to distortion, so far the Panasonic company hasn't demonstrated a lot of consequence. A big, heavy, expensive, and optically complex model, the Panasonic S Pro 50 mm f/1.4 practically didn't correct this aberration at all. A much cheaper, smaller, simpler device, the Panasonic S 50 mm f/1.8, managed to correct it almost completely.In case of the Panasonic S 85 mm f/1.8 we expected a similar approach as in case of the 1.8/50 model. After all the 85 mm focal length is not especially demanding. Our measurements for corrected JPEG files seemed to confirm that way of thinking, with just traces of barrel distortion of -0.14%. Within the measuring error it is a result in accordance with zero.
The situation for RAW files, with pincushion distortion of +1.14%, surprised us a bit. It is not a value that should be considered bothersome but it's worth noticing that the Sony FE 85 mm f/1.8 had a distinctly lower level, that of +0.34%, and the Nikkor Z 85 mm f/1.8 S had a result of +0.47%. Overall, for 85 mm class lenses, a result exceeding 1% is a rarity.
| Panasonic S1R II, 85 mm, JPEG, FF | |||
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| Panasonic S1R II, 85 mm, RAW, FF | |||
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