An optical device, comprising: a light-transmitting substrate having at least two major surfaces parallel to each other and edges; optical means for coupling light into said light-transmitting substrate, and at least one reflecting surface located in said light-transmitting substrate which is non-parallel to said major surfaces of the light-transmitting substrate, characterized in that said optical means for coupling light into said light-transmitting substrate is a partially reflecting surface illuminated by a collimated display emanating from a light source, wherein said partially reflecting surface is parallel to said at least one reflecting surface, wherein a) part of the light coupled into the light-transmitting substrate passes through the partially reflecting surface out of said light-transmitting substrate, b) part of said light is reflected by said partially reflecting surface directly into said at least one reflecting surface which couples the light out of said light-transmitting substrate and c) part of said light is reflected into the light-transmitting substrate by one of said at least two major surfaces of said light transmitting substrate and further reflected at least once by total internal reflection and coupled out of the light-transmitting substrate by said at least one reflecting surface, after reflection off at least one of the major surfaces of the light-transmitting substrate. a light-transmitting substrate having at least two major surfaces parallel to each other and edges; optical means for coupling light into said light-transmitting substrate, and at least one reflecting surface located in said light-transmitting substrate which is non-parallel to said major surfaces of the light-transmitting substrate, characterized in that said optical means for coupling light into said light-transmitting substrate is a partially reflecting surface illuminated by a collimated display emanating from a light source, wherein said partially reflecting surface is parallel to said at least one reflecting surface, wherein a) part of the light coupled into the light-transmitting substrate passes through the partially reflecting surface out of said light-transmitting substrate, b) part of said light is reflected by said partially reflecting surface directly into said at least one reflecting surface which couples the light out of said light-transmitting substrate and c) part of said light is reflected into the light-transmitting substrate by one of said at least two major surfaces of said light transmitting substrate and further reflected at least once by total internal reflection and coupled out of the light-transmitting substrate by said at least one reflecting surface, after reflection off at least one of the major surfaces of the light-transmitting substrate. a) part of the light coupled into the light-transmitting substrate passes through the partially reflecting surface out of said light-transmitting substrate, b) part of said light is reflected by said partially reflecting surface directly into said at least one reflecting surface which couples the light out of said light-transmitting substrate and c) part of said light is reflected into the light-transmitting substrate by one of said at least two major surfaces of said light transmitting substrate and further reflected at least once by total internal reflection and coupled out of the light-transmitting substrate by said at least one reflecting surface, after reflection off at least one of the major surfaces of the light-transmitting substrate.