PSF & Seeing

The Point Spread Function (PSF) describes how a point source appears in an image.

Diffraction Limit: The Airy disk pattern arises from diffraction through the circular telescope aperture. Angular resolution: θ = 1.22λ/D.

Atmospheric Seeing: Turbulence in Earth's atmosphere causes wavefront distortions, blurring images with a Gaussian profile. FWHM typically 0.5-2 arcsec.

Combined PSF: The observed PSF is the convolution of the Airy disk with atmospheric seeing. For ground-based telescopes, seeing usually dominates.

FWHM: Full Width at Half Maximum - the angular width where intensity drops to 50% of peak. Key metric for image quality.

Encircled Energy: Fraction of total light within a given radius. Important for aperture photometry.