[en] The Jodrell Bank VLA Astrometric Survey (JVAS) and the Cosmic Lens All-Sky Survey (CLASS) aim to observe 10,000 flat spectrum radio sources. So far approximately 7,500 have been observed with the VLA and mapped with a resolution of 0.2 arcseconds. One of the main objectives of the surveys is to obtain reliable statistics on the frequency and properties of lens systems for cosmological studies---Hubble's constant may be derived from time delays between variations of lens images and the cosmological constant from lensing statistics.
