Gravitational lensing has played an important role in cosmology since the discovery of the first gravitational lensing system in 1979 (Walsh et al.), where the quasar QSO 0957+561 can be seen in two images. Such multiple images of a distant source will typically have an image separation of a few arcseconds.
This thesis is built on a sample of 201 quasars observed at the NOT in the period 1994-1995. The goal has been to discover new gravitational lensing candidates among these quasars. A PSF subtraction could be performed on 173 of the quasars to uncover close and faint images.