A head-up display for a vehicle having a window, the head-up display comprising: a picture generating unit arranged to output pictures, wherein each picture comprises a first picture component and a second picture component; a projection engine arranged to receive the pictures output by the picture generating unit and project the pictures onto the window of the vehicle in order to form a first virtual image of the first picture component at a first virtual image distance from a viewing plane and a second virtual image of the second picture component at a second virtual image distance from the viewing plane, wherein light of the first picture component is polarised in a first polarisation direction and light of the second picture component is polarised in a second polarisation direction perpendicular to the first polarisation direction, wherein the projection engine comprises an optical element arranged to receive light of the first picture component and light of the second picture component, wherein the optical element has first optical power in the first polarisation direction and second optical power in the second polarisation direction such that the first virtual image distance is not equal to the second virtual image distance, wherein the light of the first picture component forms a first light footprint on the optical element and light of the second picture component forms a second light footprint on the optical element, wherein the first light footprint and second light footprint at least partially overlap; wherein the projection engine is arranged such that the light ray bundle that will form the second virtual image at the second virtual image distance is at least partially contained within the light ray bundle that will form the first virtual image at the first virtual image distance received by the optical element, when said first and second light ray bundles are received by the optical element; wherein the optical element is a polarisation-selective mirror having a first surface and second surface, wherein the first surface is reflective in the first polarisation direction and transmissive in the second polarisation direction, and the second surface is reflective in the second polarisation direction; and wherein the first surface has the first optical power and the second surface has the second optical power. a picture generating unit arranged to output pictures, wherein each picture comprises a first picture component and a second picture component; a projection engine arranged to receive the pictures output by the picture generating unit and project the pictures onto the window of the vehicle in order to form a first virtual image of the first picture component at a first virtual image distance from a viewing plane and a second virtual image of the second picture component at a second virtual image distance from the viewing plane, wherein light of the first picture component is polarised in a first polarisation direction and light of the second picture component is polarised in a second polarisation direction perpendicular to the first polarisation direction, wherein the projection engine comprises an optical element arranged to receive light of the first picture component and light of the second picture component, wherein the optical element has first optical power in the first polarisation direction and second optical power in the second polarisation direction such that the first virtual image distance is not equal to the second virtual image distance, wherein the light of the first picture component forms a first light footprint on the optical element and light of the second picture component forms a second light footprint on the optical element, wherein the first light footprint and second light footprint at least partially overlap; wherein the projection engine is arranged such that the light ray bundle that will form the second virtual image at the second virtual image distance is at least partially contained within the light ray bundle that will form the first virtual image at the first virtual image distance received by the optical element, when said first and second light ray bundles are received by the optical element; wherein the optical element is a polarisation-selective mirror having a first surface and second surface, wherein the first surface is reflective in the first polarisation direction and transmissive in the second polarisation direction, and the second surface is reflective in the second polarisation direction; and wherein the first surface has the first optical power and the second surface has the second optical power.