Carl-Zeiss Vario-Tessar T* E 16-70mm f/4 ZA OSS ( Sony SEL1670Z ) - Review / Test Report - Analysis
Lens Reviews -
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As a user you can select whether your images shall be auto-corrected or stick to the original quality of the lens. In auto-corrected mode, there is, unsurprisingly, nothing to worry about (at the expense of field-of view). However, the situation changes when looking at the original characteristic of the lens. It shows a rather heavy ~3.1% barrel distortion at 16mm and moderate pincushion distortion at and beyond 40mm. The two opposing forces even out around the 24mm mark. This is about typical in this lens class though.
The uncorrected vignetting is rather extreme at 16mm at fully open aperture - an indication that the lens is somewhat underdesigned actually. Stopping down reduces the issue but in critical scenes, the light falloff remains visible even at f/11. This also applies to 24mm @ f/4 but otherwise it is not much of an issue anymore.
Of course, the situation changes again when using the lens with activated image auto-corrections where these flaws are (mostly) taken care of (at the expense of increased sensor noise in the corners).
At the end of the day, we want a standard zoom lens to be sharp but we are sorry to say it - this is where the Zeiss lens fails. Or to be precise: it is actually great if not outstanding in the image center but the outer image field is often disappointing. The quality is mediocre at 16mm, not so hot at 24mm @ f/4 and 40mm @ f/4 but beyond believe at 70mm really. Stopping down helps to improve the borders/corners but the 70mm setting remains miserable. In our disbelieve we send the lens to the local Sony service TWICE and they confirmed that it is within their factory specs. Since readers have been criticizing us for having used the Sony NEX 7 in the past, we also switched to the A6000 this time just to make sure that it is not the camera.
Note: This lens was purchased in a normal shop just like average Joe would do. It was not provided by Sony/Zeiss.
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)
Lateral CAs can be auto-corrected either by the camera or via various RAW converter. This is a lossless operation and it's a good idea to take advantage with the Zeiss lens. The original CAs are high at 16mm. Beyond the issue eases and the CAs aren't too bad considering the 24 megapixel scope actually.
Just to give you a visual for the CA situation at 16mm f/11: