Changes

<p>In <a title="Optics" href="http://en.wikipedia.org/wiki/Optics">optics</a>, <strong>astigmatism</strong> (from <a title="Greek language" href="http://en.wikipedia.org/wiki/Greek_language">Greek</a>: &alpha;- <em>a-</em> &quot;without&quot; + &sigma;&tau;ί&gamma;&mu;&alpha;&tau;&omicron;&sigmaf; <em>stigmatos</em>, gen. of &sigma;&tau;ί&gamma;&mu;&alpha; <em>stigma</em> &quot;a mark, spot, puncture&quot;<sup class="reference" id="_ref-0"><a title="" href="http://en.wikipedia.org/wiki/Astigmatism#_note-0">[1]</a></sup>) is when an optical system has different <a title="Focus (optics)" href="http://en.wikipedia.org/wiki/Focus_%28optics%29">foci</a> for <a title="Ray (optics)" href="http://en.wikipedia.org/wiki/Ray_%28optics%29">rays</a> that propagate in two perpendicular <a title="Plane (mathematics)" href="http://en.wikipedia.org/wiki/Plane_%28mathematics%29">planes</a>. If an optical system with astigmatism is used to form an image of a <a title="Cross" href="http://en.wikipedia.org/wiki/Cross">cross</a>, the vertical and horizontal lines will be in sharp focus at two different distances.</p>

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<h2><span class="mw-headline">Forms of astigmatism</span></h2>