Airy disk
<p>Jul 01, 2014 04:52 PM</p>
<p>
see discussion under "human eye"</p>
<p>
The maximum density of cones in the human <a title="Fovea" class="mw-redirect" href="http://en.wikipedia.org/wiki/Fovea">fovea</a> is approximately <b>170,000 per square millime</b>ter,<sup class="reference" id="cite_ref-10"><a href="http://en.wikipedia.org/wiki/Airy_disk#cite_note-10">[10]</a></sup> which implies that the <b>cone spacing in the human eye is about 2.5 μm</b>, approximately the diameter of the point spread function at f/5.</p>