Venus Optics LAOWA Argus 28 mm f/1.2 FF
6. Distortion and field of view
Field of view
A rectilinar 28 mm lens on full frame should provide an angle of view of exactly 75.4 degrees and this value exactly the producers declare in the official specifications. We decided to check that claim. In order to do that we took photos of starry sky, saved as uncorrected JPEG files, and 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 236 stars positioned uniformly across the frame, with the relative mesh-fitting error of 1 minute and 55 seconds of arc.Finally our result amounts to 75.0 deg with an error of 0.1 deg, so slightly narrower than the declarations of the producer but the difference is really slight.
Distortion
The Argus 1.2/28 FF shows slight barrel distortion which, on the APS-C/DX sensor, amounts to -1.21% and on full frame it increases slightly to -1.39%. A slight difference between these results stems from the fact that a bit of moustache distortion has been introduced as well. If you limit your measurements to the 1:1 area on full frame, where there are no bent lines characteristic for moustache distortion, the result increases to -1.98%.
All these values are not especially high and/or bothersome. Even though distortion is not corrected in a perfect way we are overall pleased that it is optics of the Argus that deals with it, not sorely the software of the camera.
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| Nikon Z7, 28 mm, JPEG, APS-C/DX, | |||
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| Nikon Z7, 28 mm, JPEG, FF | |||
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