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Laowa 7.5mm f/2 MFT C-Dreamer - Review / Test - Analysis |
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Lens Reviews -
(Micro-)Four-Thirds
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Page 2 of 3
Distortion
The Laowa 7.5mm f/2 MFT produces a medium to strong barrel distortion of 2.9%. Remember that this is the native characteristic without any digital trickery.
Vignetting
It seems as if the optical design of the lens has one drawback - heavy vignetting. At f/2 we measured a light falloff of 2.5EV (f-stops). While this may be normal on full format cameras, it is almost double the amount that we've seen from other ultra-wide MFT lenses. Stopping down to f/2.8 helps a bit but you should chose at least f/4, better f/5.6 to tame the issue.
Now that being said, this sounds worse than it actually is because the light falloff is fairly gradual. Below are (downsized) grey images below taken at f/2 (left) and f/2.8 (right) respectively.
 
MTF (resolution)
Considering its design objectives, the Laowa 7.5mm f/2 MFT has an impressive resolution characteristic. The center quality is already great at f/2. The borders are good whereas the extreme corners are fairly soft. That was to be expected at such a large aperture settings. Stopping down to f/2.8 increases the quality especially in the corners. The sweet spot is reached between f/4 to f/5.6 where even the corners are boosted to good to very good quality. Diffraction has a moderate impact at f/8 but you shouldn't stop down further unless it's really required for your scene.
The tested sample had an Okay centering quality. The field curvature is moderate.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness.
If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations
Chromatic Aberrations (CAs)
Lateral CAs (color shadows at harsh contrast transitions) are reasonable well managed with an average pixel width of around 1px at the image borders (somewhat higher on the left image side in our prototype sample).
Flare
Back-light scenes are a bit of a challenge for the little Laowa lens. Ghostings and/or glare can be an issue at times - see below.
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