### point-spread function

**(PSF)**
(function describing an optical system's response to a point of light)

A **point-spread function** (**PSF**) is a description of the
response of an optical system (such as a telescope) to
incoming light from a point, consisting of a mathematical
function describing the light-pattern expected on the focal plane,
i.e., mapping relative position on the focal plane to the received EMR
flux that would come from a point source. Such a function
describing an Airy disk is an example. Theories have been
developed regarding types of mathematical functions specific to
particular aperture shapes (e.g., rectangles, slits, circles)
and sizes: **masks** are sometimes used with telescopes producing
various shapes because non-circular apertures in some cases reveal
data obscured by circular apertures.

**PSF subtraction** (for **point spread function subtraction**) is a
type of post-processing aimed at isolating the Airy disk of a
specific star. Airy disks from images of lone stars taken with the
same instrument are then used to help sort out the images of the
stars with overlapping Airy disks.

(*telescopes,optics,function*)
**Further reading:**

http://en.wikipedia.org/wiki/Point_spread_function

http://www.stsci.edu/itt/review/dhb_v4/NICMOS/nic_ch56.html

**Referenced by pages:**

PSF fitting

speckle suppression

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