Voigtlander Heliar 75mm f/1.8 on Sony NEX - Review / Test Report - Analysis
Lens Reviews - Sony NEX

Distortion

The Voigtlander lens produces a marginal amount of barrel distortion (~0.3%) which is irrelevant in field conditions.

Vignetting

The Heliar is a full format lens and enjoys a sweet spot advantage on the APS-C format NEX system. This shows up in the vignetting chart. At f/1.8 there's a bit light falloff (0.7EV) but it's far from extreme and basically gone from f/2.8 onward.

MTF (resolution)

The Heliar 75mm f/1.8 managed to provide pretty good resolution figures on the difficult NEX 7 sensor system. At max. aperture the center is already very fine although the border region is plain soft. The contrast level is slightly reduced here. At f/2.8 the borders/corner recover a bit to acceptable levels. The lens performance truly shines between f/4 and f/8 with a very good performance across the image frame. Diffraction has a slight dampening effect at f/11 - as usual.

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 CAs (color shadows at harsh contrast transitions) are well controlled with an average width of between ~0.7px at f/1.8 and about 1px at medium aperture settings. This is quite impressive on such a high pixel density sensor.

Bokeh

A very important aspect of an ultra-large aperture lens is the quality of the bokeh (rendering of the out-of-focus blur). The Heliar delivers pretty good here.

The foreground blur is a bit nervous but the more important background blur is smoother.

Out-of-focus highlights show a slight outlining effect at f/1.8 but the inner zone is otherwise very even. The outlining is gone at f/2.8.

Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)

Bokeh fringing is a common issue with fast glass. It's visible as halos of different colors in out-of-focus areas - magenta (red + blue) in front of the focus point and green beyond. The Heliar 75mm f/1.8 shows noticeable bokeh fringing at large aperture settings but it's still present at f/4.

You may notice some focus shift (residual spherical aberrations) when moving across the different aperture marks below. If you stop down prior of focusing this is rather irrelevant on the Sony NEX - it may be an issue in its native Leica scope though.

There is some visible softness at f/1.8 - this is surely related to some performance deterioration at close focus distance but remember this is also a shallow depth-of-field setup so don't over-interpret this.

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




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