We present a profilometry technique for smooth surfaces based on the reflection law. In general, it is difficult to use point detectors for this task due to the spreading of the beam after reflection. Our point detector technique consists of controlling the spreading of the laser beam by analyzing the diffraction of the light through the system. Our analysis enables us to control the spreading of the beam even for a large local curvature of the object under test. The curvature and the distance of the object from the focusing lens are the main parameters to control the resulting spot size of the beam at the detection plane. Once point-like projections are obtained at the detection plane, a novel algorithm is used to calculate the surface profile via computing the local surface slope. The proposed technique is intended for smooth surfaces, such as the testing of convex plates and mirrors or the detection of irregularities in machined parts. It does not require any especial preparation of the surface or extensive alignment of the system. We illustrate our technique by showing experimental measurements of a smooth convex profile. For this, we use a ball bearing.