Reduction of residual coma and astigmatism in a 1$middot$5 m Czerny-Turner spectrometer

Ray tracing calculations have been performed in order to evaluate the geometrical aberrations of a high resolution 1·5 m in-plane Czerny-Turner spectrometer using spherical mirrors and a high blaze angle Echelle grating. Results show that for minimum instrumental broadening the focusing mirror off-axis angle must satisfy the Rosendahl cos 3 relation, that the astigmatism can be reduced by using divergent grating illumination, and that circular slits can still be used to eliminate the inherent spectral line curvature.