Leica Summarit-M 50mm f/2.5 on Sony NEX - Review / Lens Test Report - Analysis
Lens Reviews - Sony Alpha/NEX (APS-C)

Distortion

The Summarit produces a negligible amount of pincushion distortion (~0.05%) which is irrelevant in field conditions.

Vignetting

Typical for full format lenses it has a walk-over on APS-C cameras with respect to light fall-off. Even at f/2.5 it's barely something worry about in real world situations and it's absolutely negligible from f/2.8 onwards.

MTF (resolution)

The Leica lens delivers an impressive resolution characteristic across the tested aperture range. The center quality is already very good at f/2.5 and the borders follow on a good level here. There's a boost in quality at f/4 - the center is lifted to excellent quality and the borders are also very sharp. 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 are very well controlled at large aperture at less at 1px on the average pixel at the image borders. However, the CA pixel width increases steady the more you stop down and the CAs get slightly more obvious at f/8 and f/11.

Bokeh

The quality of the bokeh (out-of-focus blur) is, of course, a primary aspect of a fast prime lens. The Summarit produces a very decent bokeh. 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 The issue dissolves from f/4 onwards.

Upon closer observation you may also be able to spot a fairly obvious focus shift towards the background when stopping down - this is rather typical for 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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