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Lens review

Sigma C 56 mm f/1.4 DC DN

22 December 2018
Maciej Latao

7. Coma, astigmatism and bokeh

Coma is not corrected in a perfect way, a fact easy to discern while glancing at photos below. By f/1.4 you can notice it without a problem although it decreases on stopping down the lens to f/2.0. Still even at that place you can spot slight deformation of diode images.

A7RII, f/1.4, center A7RII, f/1.4, corner
Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh
A7RII, f/2.0, center A7RII, f/2.0, corner
Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh


Astigmatism, understood as average difference between horizontal and vertical MTF50 function values, amounted to 5.6% so its influence on image quality is slight.

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When it comes to out-of-focus areas the light spread is quite smooth and even, with onion-ring bokeh, connected to the aspherical element, barely visible, and just a moderately accented rim. Still, quite distinct mechanical vignetting is a problem.

A7RII, f/1.4, center A7RII, f/1.4, corner
Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh
A7RII, f/2.0, center A7RII, f/2.0, corner
Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh
A7RII, f/2.8, center A7RII, f/2.8, corner
Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh Sigma C 56 mm f/1.4 DC DN - Coma, astigmatism and bokeh