A system for determining the topography of a diffusely reflecting curved surface, comprising two telecentric projection branches that independently and successively project fringe images of a Ronchi grating on the diffusely reflecting curved surface and a viewing branch of which the optical system projects an image of the diffusely reflecting curved surface on its camera target, further comprising a computer that receives the fringe images recorded by the camera target and calculates the topography of the diffusely reflecting curved surface, characterized in - that each of the projection branches comprise a fringe projector that comprises the following components listed according to the propagation direction of the light; a semiconductor diode that emits radiation with a wavelength around a central value smaller than 500nm, a filter glass that transmits no radiation of a wavelength longer than said wavelength, a condenser lens, a Ronchi grating mounted in a fitting that can rotate the grating around the optical axis, a slit diaphragm that selects the lowest diffraction orders of the Ronchi grating, and that has its axial position in the front focal plane of a projection lens that projects filtered images of the Ronchi grating on a projection plane that touches the diffusely reflecting curved surface - that the optical axes of the projection branches and the viewing branch lie in one plane; - that the angles between the axes of the projection branches and the viewing branch are equal and opposite and that the three axes intersect in one point; - that the optical system of the viewing branch is telecentric in its object space and its image space and transmits light of a wavelength longer than 500 nm; - that a focusing tool is included in the system, said focusing tool comprising two narrow beams and focused from different angles on the surface to be measured; and - in that the system is configured to project the fringe images with time intervals between the two exposures of milliseconds - that each of the projection branches comprise a fringe projector that comprises the following components listed according to the propagation direction of the light; a semiconductor diode that emits radiation with a wavelength around a central value smaller than 500nm, a filter glass that transmits no radiation of a wavelength longer than said wavelength, a condenser lens, a Ronchi grating mounted in a fitting that can rotate the grating around the optical axis, a slit diaphragm that selects the lowest diffraction orders of the Ronchi grating, and that has its axial position in the front focal plane of a projection lens that projects filtered images of the Ronchi grating on a projection plane that touches the diffusely reflecting curved surface - that the optical axes of the projection branches and the viewing branch lie in one plane; - that the angles between the axes of the projection branches and the viewing branch are equal and opposite and that the three axes intersect in one point; - that the optical system of the viewing branch is telecentric in its object space and its image space and transmits light of a wavelength longer than 500 nm; - that a focusing tool is included in the system, said focusing tool comprising two narrow beams and focused from different angles on the surface to be measured; and - in that the system is configured to project the fringe images with time intervals between the two exposures of milliseconds