Sigma C 65 mm f/2 DG DN
5. Chromatic and spherical aberration
Chromatic aberration
The optical construction of the Sigma C 2/65 features just one low dispersion ED glass element and, it seems, it's not enough to eliminate longitudinal chromatic aberration completely. Its influence, in a form of slight colouring of out-of-focus images, can be noticed mainly near the maximum relative aperture. Fortunately, it's not a very serious or even moderately serious flaw. |
What about lateral chromatic aberration? Let's glance at a graph below and find out.
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Its highest level is reached near the maximum relative aperture bu even there the results can be placed on a borderline between very low and low level. On stopping down they drop below 0.04% and it means that aberration becomes practically imperceptible.
| A7R III, RAW, FF, f/2.0 | A7R III, RAW, FF, f/8.0 |
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Spherical aberration
First photos of this chapter don't show any noticeable 'focus shift' effect. When it comes to circles of light reached before and behind the focal point they aren't identical. In fact you can notice a textbook example of spherical aberration that hasn't been corrected properly well - the edge of one circle is soft and the second circle features a brighter rim.
| A7R III, f/2.0, before | A7R III, f/2.0, after |
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