An optical system and a lens for railway signals are provided. The optical system comprises a frontal (1b) and a rear (1a) body section, wherein the rear body section (1a) comprises a light source (2) comprising one or more light-emitting diodes, a rear lens (4), and a light-absorbing structure (8) surrounding the rear lens (4). The frontal body section (lb) comprises a converging frontal lens arrangement (11), and a casing connecting the frontal lens arrangement (11) to the rear body section (la). The rear lens (4) is configured to pass light collected from the light source (2) towards the frontal lens arrangement (11). The rear lens (4) comprises a cut-out (15) under a substantially horizontal line below its center, and the light-absorbing structure (8) surrounding the rear lens (4) covers the cut-out of the rear lens (4), and is configured to absorb light coming from the direction of the frontal lens arrangement (11).