A lens system which forms image of a point source object is called as point spread function (or) PSF. Point spread function is also called as Fraunhofer diffraction pattern, impulse response and Green’s function.

Figure: Above figure was generated by Zemax

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$\quicklatex{color="#000000" size=25} E_{\left(ip\right)}=\ E_{\left(ip\right)}\left(0\right){\left[\frac{{2J}_1\left({\pi q^'}/{\lambda F}\right)}{\left({\pi q^'}/{\lambda F}\right)}\right]}^2$

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 Eip – Image irradiance, J1 – Bessel function, λ – Wavelength

## Properties of point spread function (PSF):

• PSF can be computed from pupil function by squaring its fourier transform.
• Peak irradiance of PSF strongly depends on wavelength λ.
• PSF forms depends upon the shape of the pupil boundaries.

Reference:

Robert R. Shannon and James C. Wyant, “Applied optics and Optical engineering”, Academic press, Inc. Vol. 7, ISBN 0-12-408608-X (v. 8), 1980.