Kowa Prominar MFT 12mm f/1.8 - Review / Lens Test - Analysis
Lens Reviews - (Micro-)Four-Thirds
Article Index
Introduction
Analysis

Distortion

Unlike most MFT lenses, the Kowa Prominar series is fully corrected - thus it doesn't rely on image auto-correction. The latter is also not possible due to the lack of EXIF information anyway. As usual Kowa did a good job in terms of distortion. The Prominar 12mm f/1.8 shows a barrel distortion of 1.1% which is low for such a lens even by DSLR standards.

Vignetting

The vignetting is a weakness of the lens. A light falloff of 1.6EV (f-stops) at f/1.8 is clearly visible. Stopping down helps a bit but not quite as much as you would have hoped for (minimum 1EV).

MTF (resolution)

In terms of resolution we have a mixed beast here. Technically the lens is capable of delivering a sharp center even at f/1.8 whereas the outer image region is Okay. However, this is not the complete story here because field curvature is spoiling the game at this setting. If you are taking pictures of flat objects at large aperture settings, the corners will be extremely soft. This improves when stopping down but it remains an issue at f/2.8, a bit less so beyond. The peak performance is reached between f/4 and f/5.6 where even the corners are very good. Diffraction has a higher impact from f/11.

The tested sample had a sub-average centering quality which is also why we don't provide sample images this time.

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 quite well controlled. They are barely visible at f/1.8 but increase when stopping down. However, even at f/8 they aren't really an issue with an average width of 1px at the image borders.

Verdict

The Kowa Prominar MFT 12mm f/1.8 is the weakest offering in the Kowa lineup. The pure MTFs are actually quite decent. The center is always sharp at the mainstream settings and the outer image region is relatively decent at f/1.8, good at f/2.8 and very good between f/4 and f/8. However, field curvature is a major issue at large apertures so in the real life the results are less convincing here - at least in our sample which wasn't really well centered. Typical for the three initial Prominar lenses, both the distortion as well as the lateral CAs are low which is good because image auto-correction isn't possible. The amount of vignetting is generally on the high side though.

The mechanical quality of the Kowa lens is, again, impressive. It feels like a lens from the good ol' days - in a positive way. The lens body is made of metal and the controls are smooth as silk. However, a weather sealing is missing. As aspect that is probably going to be less popular is the lack of AF and an electronically couple aperture. However, thanks to its unique Dual Link Iris, the aperture ring can be changed to a movie-friendly mode (smooth settings rather than clicks) so this can make some sense.

So where does this leave us? Honestly, for mainstream photography we'd rather stick to the Olympus M.Zuiko 12mm f/2. For movies we are having some doubts here as well - in this scope it faces some headwind from the Samyang 12mm T2.2 VDSLR NCS CS for instance. Thus we don't really see a compelling value proposition here.

Optical Quality: (down-rated due to field curvature)
Mechanical Quality:
Price/Performance:
      
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