Zeiss ZE Distagon T* 25mm f/2 (Canon EF) - Review / Lab Test - Analysis
Lens Reviews -
Canon EOS (Full Format)
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The Zeiss Distagon T* 25mm f/2 produces a moderate degree (~1.8%) of barrel distortion. This is about average for a prime lens in this class and also identical to the older Distagon T* 25mm f/2.8.
The vignetting characteristic seems to be a real weakness of Zeiss Z-series lenses when used on full format DSLRs. The Distagon shows a fairly extreme deterioration of ~2.6EV at f/2 - this will be visible in most scenes. The problem is still very pronounced at f/2.8 (@ ~1.7EV) but it's not overly significant anymore from f/5.6 onwards.
The Zeiss lens produced very high resolution figures in the MTF lab. The center quality is nothing short of stunning with extremely high resolution combined with snappy contrast straight from f/2. The lens is certainly easily capable of exceeding the quality of the sensor (EOS 5D II) here. The border quality is a bit weaker with very good results and the corners are softer still. Stopping down to f/2.8 has no major effect but there's a more substantial boost at f/4. The peak performance is reached around f/5.6 with a very sharp image quality across the image frame. The quality level is kept at f/8 whereas diffraction reduces the potential from f/11 onward.
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)
Zeiss claims to have substantially reduced lateral CAs (color shadows at harsh contrast transitions) on this lens and they are indeed on an extremely low level of just 0.3px on the average at the image borders. This is not field-relevant anymore.