EXCERPT page containing first few paragraphs. 2020-01-25 15:11:56
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Sigma discusses axial (longitudinal) chromatic aberration:
For axial chromatic aberration that is hard to correct even during the image processing, SLD (Special Low Dispersion) glass elements are incorporated, ensuring high image quality throughout the entire focusing range. The lens achieves sharp and high contrast image rendering.
Other than spherical aberration which is generally well controlled by aspheric element(s), the dominant contrast-degrading aberration for fast lenses at wide apertures is longitudinal chromatic aberration (LOCA).
LOCA is responsible for the dreaded violet fringing, but that violet halo effect is only made obvious with some subject matter. It can look awful in backlighting, but for many images it simply will not be seen.
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