Originally Posted by
neuroanatomist
The numbers on the chart are pretty sharp - sharp enough that I'd say
focus cannot be "way off," as you suggest. Rather, I suggest instead
that the purple cast is truelongitudinal (axial)CA - the fact that
stopping down progressively improves the fringing is consistent with
that suggestion. In fact, a slight defocusing would actuallyimprovelongitudinalCA,
rather than making it worse. Also note that this is a flat chart -
we're not talking about 'bokeh fringing' here. As a side note,
technically CA applies only in the plane of sharp focus, since by
definition an aberration affects only what is in focus. But as the term
is commonly applied, I'd call the fringing on both the Nikkor and the
Zeiss lenses longitudinal CA, and not due to missed focus.<span class="field-item-description"]