Zeiss Distagon T* 18mm f/3.5 ZF (DX) - Review / Lab Test Report - Analysis
Lens Reviews -
Nikon / Nikkor (APS-C)
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The Zeiss Distagon 18mm f/3.5 produces a moderate degree (~1.8%) of barrel distortion. Unlike on FX, the barrel distortion is uniform on the DX sensor and thus a lot easier to remove in post processing.
The chart above has a real-world size of about 120x80cm.
The lens shows quite pronounced vignetting wide open on our DX test camera, however stopped down to f/5.6 and beyond corner darkening is no longer an issue for most subjects.
The Zeiss delivers very good resolution in the center wide open. Stopping down lifts the sharpness to excellent values, while diffraction reduces it again from f/11 onwards.
The borders start softer wide open with good resolution, while the extreme corners show even less sharpness at this aperture setting. Stopping down increases sharpness considerably, the peak performance is reached at f/8 here.
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
Chromatic Aberrations (CAs)
Chromatic aberrations (color shadows at harsh contrast transitions) are moderate at less up to 1.8px on the average at the image borders. This is not unusually high for an ultra wide-angle lens although the problem will be visible at times. It is, of course, possible to correct lateral CAs in most modern RAW converters. Many modern Nikon DSLRs already do this for you in-camera if you shoot JPG.
Full size sample images are available in our FX review of this lens.
On FX the Zeiss Distagon T* 18mm f/3.5 ZF offers an affordable and wider alternative to the "legendary" Distagon 21mm. On DX however, it loses most of its appeal. It's still a wide angle lens here, but with a focal length that is also offered by lots of dedicated DX zoom lenses. The resolution figures are good to excellent in the image center, but the borders and corners deliver less sharpness than one would expect from a lens carrying such a highly regarded brand name. The amount of barrel distortion is moderate, lateral CAs are comparatively well controlled albeit visible at times. A surprising weakness is the amount of vignetting which is quite pronounced at f/3.5 - a rather typical flaw of the Zeiss Z-series it seems. However, it's not overly annoying at medium aperture settings.
Just like the rest of its family, the Zeiss lens is built to the highest standards. Some users may complain about the lack of AF but the focus confirmation is available in the viewfinder and in very critical (for example close focus) scenes Live-View can give you the needed guidance. That said, it remains a bit of an anachronism these days. The price level is quite steep in absolute terms but it's not all that bad in comparison to other FX wide angle lenses. For DX only shooters however, there are certainly more affordable options available that also offer AF.