Sony 135mm f/2.8 [T4.5] STF ( SAL-135F28 ) - Review / Test Report - Analysis
Lens Reviews - Sony Alpha/NEX (APS-C)

Distortion

Typical for fix-focal length lenses in this range the amount of distortion is absolutely negligible (~0.13%).

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

Vignetting

The 135mm f/2.8 STF is a full format lens and as such enjoying the usual sweet spot advantage when used on an APS-C DSLR. The amount of vignetting is basically non-existent within this scope - even at T/4.5 (f/2.8).

MTF (resolution)

The lens produced outstanding resolution figures in the MTF lab. The quality is already exceptionally high and very even at T/4.5 (f/2.8) both in terms of contrast and level of detail. The performance peak is reached at T/5.6 (f/3.5). Beyond diffraction is the limiting factor.

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 very well controlled with an average CA-pixel width (@ the borders) around 0.4px. This is usually nothing to worry about in field conditions.

Purple Fringing

At max. aperture the lens is slightly prone to produce purple fringing in extreme contrast situations. This is not unusual for large aperture lenses but it can be disturbing at times.

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. You may notice the slightly magenta-to-green color shift in the foreground and background of the sample crops below. The effect is gone by T/8.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
T/4.5 T/5.6 T/8

Bokeh

As mentioned the design of the lens has been optimized to achieve a silky bokeh (out-of-focus blur) and the STF does not disappoint here. At T/4.5 (f/2.8) the bokeh is smoother than on any other lens tested to date. As expected the effect deteriorates somewhat when stopping down but usually you will prefer to use the max. aperture anyway.




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