Lens review

Voigtlander Color Skopar 28 mm f/2.8 SL II

6 April 2013
Arkadiusz Olech

7. Coma, astigmatism and bokeh

The coma’s performance on two types of sensors is diametrically different. On the smaller one it is practically imperceptible but in the corners of the full frame it is huge and very distinct. However you shouldn’t be surprised by noticeable level of off-axis aberrations in the corners of full frame.

Voigtlander Color Skopar 28 mm f/2.8 SL II - Coma, astigmatism and bokeh

The astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounts to just 2% which is an excellent result –for a “pancake” lens simply perfect. Still we must add something that spoils that rosy image. Our resolution measurement fields are in the distance from the center of less than 20% of the field of view radius. In that area the astigmatism is corrected in a perfect way. Very serious problems, though, appear on the edge of full frame. The horizontal components of MTF50 function values can be even two times higher than those vertical ones. It is difficult to say whether it is due to the influence of astigmatism or other off-axis aberrations (particularly the lateral chromatic aberration) because the results are degenerated meaning that it is impossible to say which of the aberrations contributes to the final result and to what extent. Still undoubtedly the astigmatism is at least partially responsible for the weak image quality on the very edge of the frame and it is noticeable.

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The rings, created by strong defocusing of light points, look very well for a change. The light spread is even, without any noticeable local extremes. A rim appears on the edge of the ring but only after a significant stopping down.

Voigtlander Color Skopar 28 mm f/2.8 SL II - Coma, astigmatism and bokeh