Patent ID: 8643848

Claim:
A shape measuring method for measuring aspherical optical surfaces, comprising: irradiating a surface to be inspected and a reference spherical surface with light emitted from a light source so as to generate an interference fringe pattern produced by interference between light to be inspected reflected on the surface to be inspected and reference light reflected on the reference spherical surface; step-scanning the surface to be inspected in multiple steps along a scan axis passing through the center of curvature of the reference spherical surface; measuring a phase corresponding to a shape measurement region in the interference fringe pattern obtained using an imaging unit and measuring the wavelength of the light emitted from the light source using a wavelength measuring device in each step of the step scanning; defining a distance between any point on the surface to be inspected and the center of curvature of the reference spherical surface as a function of wavenumber including the measured phase and wavelength as parameters, calculating the wavenumber in each step from the relationship of the function between adjacent steps, and calculating the moving distance between each step; and calculating a measurement value of the distance between any point on the surface to be inspected and the center of curvature of the reference spherical surface from the calculated wavenumber and the function, calculating a design value of the distance between any point on the surface to be inspected and the center of curvature of the reference spherical surface using the calculated moving distance, and calculating a shape error of the surface to be inspected from the difference between the measurement value and the design value.