What is Focus (optics)?
[[File:DOF-ShallowDepthofField.jpg|thumb|250px|An image that is partially in focus, but mostly out of focus in varying degrees.]] In [[Geometry|geometrical]] [[optics]], a '''focus''' (also called an '''image point''') is the point where light rays that come from a point on the object converge (come together).<ref>{{cite web | title=Standard Microscopy Terminology | work=University of Minnesota Characterization Facility website | url=http://www.charfac.umn.edu/glossary/f.html | accessdate=2006-04-21}}</ref> In reality the focus is never a point but a small spot called the ''blur circle''.<ref>The smallest possible blur circle is the [[Airy disc]], which is caused by [[diffraction]] from the optical system's [[aperture]]. Aberrations tend to get worse as the aperture diameter increases, while the Airy circle is smallest for large apertures.</ref> An image, or image point or region, is '''''in focus''''' if light from object points is converged almost as much as possible in the image, and '''''out of focus''''' if light is not well converged. == References == <references/> {{sci-stub}} [[Category:Optics]] [[Category:Photography]]