Venus Optics LAOWA 6 mm f/2 Zero-D MFT
6. Distortion and field of view
Field of view
As we had photos of starry sky at our disposal we decided to measure the real field of view of the tested lens using both JPEG and uncorrected RAW files. In order to do that 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. Our transformation was based on over 140 stars positioned evenly across the frame and average mesh-fitting error amounted to one minute of arc.In order to determine the field of view you apply pixels positioned on extreme edges of the frame and, because of that, the fitting error might be a bit higher in that place. After comparing the result for both diagonals you can say that the final error didn't exceed a level of 0.1-0.2 of a degree.
In case of RAW files the field of view we got amounted to 118.9 degrees. Although JPEG files aren't distortion-corrected, images are slightly cropped when you pass from RAWs to JPEGs (as both types of files differ in resolution) so, as a result, the field of view of this second format is slightly narrower, amounting to 118.5 degrees.
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Let's remind here that the producer declares that the field of this lens is supposed to amount to 121.9 degrees so the real results are smaller. As a field of 118 deg is provided by rectilinear full frame 13 mm lenses, it seems that the real focal length of the tested Laowa is much closer to 6.5 mm than 6 mm so this device is rather an equivalent of a full frame 13 mm than 12 mm lens. Perhaps not a very significant difference but still.
Distortion
A lens providing an angle of view of about 120 deg always faces a huge challenge in the category of geometric deformations. It seems the Laowa had it even more difficult because of its small physical dimensions.Still the producers put 'ZERO-D' in the name of the lens for a reason – they took proper care to correct distortion as much as possible. Our measurements showed that you deal here with moderate barrel deformatons which level doesn't differ much as you pass from JPEG to RAW files. In case of the former we got −1.49%, and in case of the latter −1.54%. Both results dovetail within the margin of our measuring error.
The result in this category is not bad, taking the parameters of the tested lens into account, and is nothing to complain about. It should be noticed, though, that distortion here is quite untypical as vertical lines are far more deformed than horizontal lines.
| Olympus E-M5 II, 6 mm, JPEG | |||
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| Olympus E-M5 II, 6 mm, RAW | |||
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