Abstract: An interferometer for checking the shape of convex surfaces of optical components comprises a monochromatic light source and a sequence of devices arranged therebehind in the path of beams including a focusing lens, a light splitter, a compensator, a lens system having as its last surface a reference concave surface having a center of curvature optically matched with the back focus of the focusing lens by means of the compensator. Arranged in the path of beams behind the lens system are an additional compensator, an additional light splitter, an additional focusing lens, a system of mirrors for directing the beams from the monochromatic light source to the additional focusing lens having its back focus matched by means of the additional compensator with the center of curvature of the reference concave surface of the lens system closest to the monochromatic light source, the radius of curvature of this surface being other than that of the reference concave surface.