Single point diamond turning (SPDT) is one of the nanometer machining methods. We deal with the nanometer characterization of diamond-turned mirrors on the micrometer and submicrometer scale with our three-dimensional roughness measuring system based on scanning tunneling microscopy. We have studied the results of amplitude spectral density functions for these surfaces. Finally, we have calculated the total integrated scattering as a function of incident light wavelength lambda and root mean square surface roughness sigma and the diffracted angle theta(d) as a function of the lambda and the surface spatial wavelength lambda(sp). All these measurement results are the basis for improving the SPDT surface quality.