CCD Spectroheliograph of the Coimbra University

Use of the CCD chips in astronomical instruments, constructed for recording of measurements on a photographic plate, brings certain problems. These problems increase when we want to display and digitize the whole solar disk.
The spectroheliograph of the Astronomical Institute of the Coimbra University was constructed for recording of spectroheliograms of the whole solar disk on a photographic emulsion. Its construction is very accurate. Among others, it compensates perfectly the spectral line deformation in such a way that the resulting spectroheliograms are without any deformation. The compensation needs a form adjustment of the entrance, as well as of the exit slits, because they are curved. Due to the fact that it was necessary to keep the original function of the image recording on a photographic emulsion by the transition from the photographic registration to the scanning procedure with a CCD camera, we had to solve whole range of specific problems.
Above all, it concerns the necessary change of parameters of the optical system, removal of brightness and form deformations of the disk, which appeared due to the change of the recording medium. In the paper we analyze all these specific problems, we describe the possibilities of their improvement and we bring the further possibilities of the use of the spectroheliograph for measurements of the Doppler velocities.