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<blockquote data-quote="Felisek" data-source="post: 339180" data-attributes="member: 23887">Coma and chromatic aberration are somehow different things. Chromatic aberration, as you say, creates a colourful halo. This happens because the diffraction coefficient depends on wavelength, so different colours focus in different places.Coma usually refers to a distortion which affects off-axis point sources (stars or street lights), which become blurred and elongated (the name refers to a nebula around the nucleus of a comet, hence it is a coma, not comma). This is because the lens does not focus perfectly at large off-axis angles. Sometimes comatic aberration depends on the wavelength and then it can be considered a type of chromatic aberration. But usually coma refers to a different type of distortion than chromatic aberration.Coma can be a big problem in astrophotography, smearing images of stars. Also in nightscapes, where remote street lights are no longer points, but little &quot;commas&quot;.</blockquote>

[QUOTE="Felisek, post: 339180, member: 23887"] Coma and chromatic aberration are somehow different things. Chromatic aberration, as you say, creates a colourful halo. This happens because the diffraction coefficient depends on wavelength, so different colours focus in different places. Coma usually refers to a distortion which affects off-axis point sources (stars or street lights), which become blurred and elongated (the name refers to a nebula around the nucleus of a comet, hence it is a coma, not comma). This is because the lens does not focus perfectly at large off-axis angles. Sometimes comatic aberration depends on the wavelength and then it can be considered a type of chromatic aberration. But usually coma refers to a different type of distortion than chromatic aberration. Coma can be a big problem in astrophotography, smearing images of stars. Also in nightscapes, where remote street lights are no longer points, but little "commas". [/QUOTE]

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