Voigtlander Color Heliar 75mm f/2.5 (on Sony NEX) - Review / Test Report - Analysis
Lens Reviews - Sony Alpha/NEX (APS-C)

Distortion

The Color Heliar produces a slight amount of pincushion distortion (~0.7%) which is not overly field relevant.

Vignetting

Typical for full format lenses it has a walk-over on APS-C cameras with respect to light fall-off. The issue is pretty much negligible straight from f/2.5 onwards.

MTF (resolution)

The Voigtlander lens delivers very decent resolution characteristics across the tested aperture range but it's not bitingly sharp. The center quality is very good at f/2.5 and the borders follow on a good level here so it is perfectly usable here. The border quality increases till it reaches a very good maximum at f/5.6. Diffraction effects reduce the quality from f/11 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 CAs (color shadows at harsh contrast transitions) are very well controlled at less at 0.7px on the average pixel at the image borders. This is nothing to worry about in field conditions.
However, the lens can show some purple fringing in extreme situations - this problem is more difficult to correct than "normal" CAs.

Bokeh

The quality of the bokeh (out-of-focus blur) is, of course, a primary aspect of a fast prime lens and the Color Heliar manages to provide very pleasing results here. Out-of-focus highlights show a slight outlining effect at f/2.5. The quality of the blur in the critical focus transition zones is very smooth both in the image foreground and background.

Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)

LoCAs (non-coinciding focal planes of the various colors) are a common issue with relatively fast glass. As you can notice below the halos have different colors - magenta (red + blue) in front the focus point and green beyond. This is primarily a problem at f/2.5 and f/4. The issue dissolves from f/5.6 onwards.

Upon closer observation you may also be able to spot a fairly obvious focus shift towards the background when stopping down - this is a quite wide-spread problem on fast lenses.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/2.5 f/4 f/5.6




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