Zeiss Sonnar T* 135mm f/1.8 ZA (Sony SAL-135F18Z) - Full Format Review / Test Report - Analysis
Lens Reviews - Sony Alpha (Full Format)
Article Index
Introduction
Analysis

Distortion

Typical for fix-focal length lenses in this range there is virtually no distortion to worry about (~0.15%).

The chart above has a real-world size of about 120x80cm.

Vignetting

Full format sensors aren't exactly easy beings with respect to vignetting but the Zeiss is capable of delivering a good performance even at f/1.8. At around 1.3EV you will be able to notice some vignetting in the corners in certain scenes but within the full format scope this is actually pretty well controlled. The problem is basically negligible from f/2.8 onwards.

MTF (resolution)

The Zeiss 135mm f/1.8 ZA produced excellent resolution figures in the MTF lab. The center quality is already exceptionally high at f/1.8 whereas the borders and corners are somewhat weaker here (very good-). Stopping down boosts the borders which do also reach truly superb levels from f/4 onwards.

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 chromatic aberrations (color shadows at harsh contrast transitions) are exceptionally well controlled with an average CA-pixel width (border) between 0.26px @ f/1.8 and 0.5px @ f/8. Generally this is nothing to worry about in field conditions.

The lens is very resistant against purple fringing - even at f/1.8.

Bokeh

The quality of the bokeh is naturally of major interest for an ultra-large aperture lens and the Zeiss shows outstanding qualities here again. Out-of-focus highlights show a circular shape from f/1.8 up to about f/2.8. At f/4 the shape deteriorates a marginally. There's no outlining effect. The blur is exceptionally smooth and uniform. However, you may also notice the some longitudinal chromatic aberrations in the cards - more on this in the next chapter.

Background/foreground blur @ f/1.8:

Longitudinal (Axial) Chromatic Aberrations (LoCA)

LoCAs (non-coinciding focal planes of the various colors), sometimes called "bokeh CAs", can be a visible in certain situations. This not unusual for such a lens but we hoped for a better performance here regarding the 2 large ED elements in the lens design but it's obviously not enough for a true apochromatic correction (=fully color corrected).

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/1.8 f/2.8 f/4

These figures have been recycled from the older APS-C review - the characteristic remains the same on full format cameras.

Verdict

The Zeiss Sonnar T* 135mm f/1.8 ZA showed an outstanding performance within the APS-C test and it manages to keep most of these qualities on full format sensors as well. The resolution is very good at f/1.8 and great to downright phenomanal beyond. The produced contrast is also cracking straight from f/1.8. The quality of the bokeh (out-of-focus blur) is next to perfect for a conventional lens. Unfortunately longitudinal CAs, sometimes also called "bokeh fringing", can be relatively pronounced at large aperture settings - a typical problem in this lens league but a bit unfortunate nonetheless. Distortions and lateral CAs are non-issues in field conditions. Typical for full format lenses it shows some more pronounced vignetting at f/1.8 but this is still comparatively moderate and a non-issue when stopping down a little.

Thanks to an all-metal body the lens feels very solid. If you're nit-picky you may criticize the lack of sealing and a little play in the focus ring when changing the focus direction. The AF speed is still fine despite the rather dated screw-driven AF approach - a SSM drive would be a desirable enhancement though. The entry hurdle for the Zeiss T* 135mm f/1.8 ZA is quite high at around 1300EUR/US$ but if you want the very best this is the one. Highly recommended!

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