Editing Optical aberration (section)

===Aberration of lateral object points with broad pencils — coma===
By opening the stop wider, similar deviations arise for lateral points as have been already discussed for axial points; but in this case they are much more complicated.  The course of the rays in the meridional section is no longer symmetrical to the principal ray of the pencil; and on an intercepting plane there appears, instead of a luminous point, a patch of light, not symmetrical about a point, and often exhibiting a resemblance to a comet having its tail directed towards or away from the axis.  From this appearance it takes its name.  The unsymmetrical form of the meridional pencil{{snd}} formerly the only one considered{{snd}} is [[coma (optics)|coma]] in the narrower sense only; other errors of coma have been treated by [[Arthur König]] and Moritz von Rohr,<ref name=vonRohr/> and later by Allvar Gullstrand.<ref name="gullstrand1900">{{cite journal |first=Allvar |last=Gullstrand |author-link=Allvar Gullstrand |title=Allgemeine Theorie der monochromat. Aberrationen, etc. |location=Upsala |date=1900 |journal=Annalen der Physik |volume=1905 |issue=18 |page=941 | doi = 10.1002/andp.19053231504 |bibcode=1905AnP...323..941G |url=https://zenodo.org/record/2434371 }}</ref><ref name=EB1911/>