Tested: Olympus ZD 11-22 @ 11, 14 mm against Panasonic Lumix G 14mm w no accessories, w Sony wide converter, and w Panasonic wide converter.
Results:
- ZD 11-22 @ 11mm is not quite as wide as the Lumix 14 with either converter
- ZD 11-22 produces the least rectilinear distortion
- ZD 11-22 rectilinear distortion and CA, when used with E-M1, is reduced in LR 5.3 substantially when lens profile and CA correction is turned on, both become virtually nil.
- ZD 11-22 is sharper and higher contrast at corners and edges at all aperture settings, but the difference becomes small by f/5.6-f/8
- ZD 11-22 has less CA than either Lumix G 14mm
- Panasonic converter produces slightly wider FoV than Sony converter
- Panasonic converter produces more barrel distortion than Sony converter
- Sony converter produces slightly sharper results than Panasonic converter
- Sony converter produces slightly more purple fringing than Panasonic converter
It's actually amazing how well the Lumix G lens compares against the ZD 11-22 at 14mm ... the ZD 11-22 does perform better, but the results are close enough to say that for non-critical work you could pick either and not worry about it.
With the converters, the 14mm's performance is degraded a little, particularly at corners and edges, and both show increased barrel distortion. The Sony wide converter performs better overall, but shows asymmetrical aberrations which I can only conclude come from not being as well centered as the Panasonic wide converter. Because the Panasonic wide converter is actually covering a bit more FoV than the Sony, you can turn on LR's rectilinear full auto correction and then the two are almost indistinguishable—a tiny bump to contrast on the Panasonic image and the perceptual resolution difference becomes identical.
Conclusion: The Panasonic 14mm fitted with Panasonic wide converter is very small and very light weight, even compared to the same lens fitted with the Sony converter. Given some additional image processing for the Panasonic, results with either of these two can be nearly indistinguishable from the much larger and far more expensive ZD 11-22 lens.
Now ... how these results compare to the Olympus M.Zuiko 12mm f/2 I don't know, and won't without testing. But using the 14mm and either of these converters is a lot less expensive, and likely a slightly wider FoV.
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