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The Summicron 35 ASPH produces very minor pincushion distortion. With an amount of 0.3%, it's measurable in the lab, but hardly an issue in the field. For a wide-angle prime, this is impressive performance.
The chart above has a real-world size of about 120x80cm.
Vignetting is automatically corrected on digital M cameras, when the lens is either 6-bit coded or manually selected in the camera's menu. Since this correction is optional and can be switched off (by disabling lens detection), we provide both the lens' native vignetting as well as corrected figures.
The uncorrected light fall-off of the lens reaches a peak value of 2.75 stops wide open. Stopping down reduces the issue somewhat, however the vignetting figures remain on a rather high level of around 1.4 stops, even at small apertures.
When corrected by the camera, vignetting is reduced considerably. Wide open, roughly 1 stop of vignetting remains, but from f/4 onwards light fall-off is no longer an issue.
Please note that this automatic correction is also applied to the raw DNG file and (regardless of whether it is done in camera or in post) doesn't come for free. Making the image borders lighter boosts the signal level as well as the noise level, thus leading to more visible noise than if there had been no vignetting.
In the image center, the lens delivers very good resolution wide open, which increases slightly to (just) excellent figures at f/2.8. Closing the aperture another stop, sharpness virtually skyrockets and remains on this high level at f/5.6, too. From f/8 onwards, diffraction takes its toll and reduces resolution again.
The image borders and corners start out lower, with good values at the borders and just fair resolution figures at the extreme corners. By stopping down to f/5.6 both areas increase to very good sharpness.
The maximum performance in the image center is reached at f/4 already, while the most even sharpness across the whole image is achieved at f/8.
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
Chromatic Aberrations (CAs)
Chromatic aberrations (color shadows at harsh contrast transitions) are very well under control, reaching values of just above half a pixel at the image borders.
Being a rather fast lens, the Summicron allows to separate the main subject from the background. In such an image the quality of the bokeh (out-of-focus blur) is of major importance.
For a wide angle lens, the Summicron delivers quite smooth bokeh, at least at some distance behind the main subject. In the transition zone, image blur looks a little more busy, though.
Background highlights are not perfectly circular wide open and cut off towards the borders due to mechanical vignetting. Stopped down, the shape of the aperture shapes comes through and creates polygons instead of circles. There is some outlining, which remains visible throughout the tested aperture range and is not cured by stopping down.