ABSTRACT
The ability to study gravitational lenses is strongly dependant on the quality of the astronomical data. The images of a gravitationally lensed quasar are typically only a few arcseconds apart. This introduces some technical challenges, as the resolution of astronomical images is limited by both the resolution of the instruments and the turbulence of Earth’s atmosphere. The resolution of a telescope improves with increasing size and when shorter wavelength are observed. Unfortunately, the resolution of ground-based optical telescopes does not improve without limit as its size is increased. This is due to the atmospheric turbulence that produces the well-known “twinkling” of stars. As a consequence, the image of a point source (e.g. a star) is not a point, but is blurred. The observed blurring is described by the Point Spread Function (PSF), which depends on both the instrumental response and atmospheric turbulence present at the time of observation. The quality of an image of a stellar point source at a given location at a specific time is referred to as the seeing and is measured in arcseconds. The best conditions on Earth give a seeing of about 0.4 arcseconds at optical wavelengths. The atmospheric turbulence is one of the biggest problems for Earth-based astronomy: while the biggest telescopes have theoretically milli-arcsecond resolution, the real image will never be better than the average seeing during the observation. One possibility to overcome this issue is to escape the atmosphere and get the data directly from space with instruments like the Hubble Space Telescope. Another solution is to use adaptive optics which help correct for these effects, dramatically improving the resolution of ground-based telescopes. However these solutions are extremely expensive and not available for all telescopes. As a consequence, astronomers often rely on other cheaper means to improve the resolution of their data. One of them is called deconvolution.
