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<blockquote data-quote="aroy" data-source="post: 339334" data-attributes="member: 16090">Comma is the phenomenon where point sources of light are rendered as &quot;comma&quot;, that is point + a tail. Lenses meant for really low light are designed with minimal comma, so that point sources remain points. Lenses with large aperture are designed for excellent OOF (bokeh). They may or may not be designed for low light. The Nikon and Leica Noct series is designed for low light, where as the Nikon 50mm F1.2 is not.Chromatic aberration (CA) is when all the colours do not focus at a single point. This gives rise to colored fringes at the edges (it is always there but gets masked in the main body). Chromatic aberration also affects the diffraction limit, as at high F stops with fine detail, CA will create fringes, reducing resolution. That is why APO lenses tend to be sharper at higher F stops, as there is no CA fringing. Another way of looking at it is that APO lenses can be used at much higher stops before diffraction softens the image up.</blockquote>

[QUOTE="aroy, post: 339334, member: 16090"] Comma is the phenomenon where point sources of light are rendered as "comma", that is point + a tail. Lenses meant for really low light are designed with minimal comma, so that point sources remain points. Lenses with large aperture are designed for excellent OOF (bokeh). They may or may not be designed for low light. The Nikon and Leica Noct series is designed for low light, where as the Nikon 50mm F1.2 is not. Chromatic aberration (CA) is when all the colours do not focus at a single point. This gives rise to colored fringes at the edges (it is always there but gets masked in the main body). Chromatic aberration also affects the diffraction limit, as at high F stops with fine detail, CA will create fringes, reducing resolution. That is why APO lenses tend to be sharper at higher F stops, as there is no CA fringing. Another way of looking at it is that APO lenses can be used at much higher stops before diffraction softens the image up. [/QUOTE]

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