A method of determining a shape of an optical test surface (14) includes: with adaptation optics (20), adapting a wavefront of a measuring beam (30) to a desired shape of the optical test surface (14), interferometrically measuring the shape of the optical test surface (14) with the adapted measuring beam, irradiating the adapted measuring beam at different angles of incidence onto the optical test surface and respectively measuring the wavefront of the measuring beam after the interaction of the measuring beam with the optical test surface (14), establishing the effect of the adaptation optics (20) upon the interferometric measurement result from the wavefronts measured for the individual angles of incidence, and determining the shape of the optical test surface (14) by removing the established effect of the adaptation optics (20) from the interferometric measurement result.