Sigma C 56 mm f/1.4 DC DN review - Coma, astigmatism and bokeh

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Sigma C 56 mm f/1.4 DC DN

22 December 2018

Arkadiusz Olech

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.

A7R II, f/1.4, center	A7R II, f/1.4, corner

A7R II, f/2.0, center	A7R II, f/2.0, corner

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.

A7R II, f/1.4, center	A7R II, f/1.4, corner

A7R II, f/2.0, center	A7R II, f/2.0, corner

A7R II, f/2.8, center	A7R II, f/2.8, corner