Prototype reflecting coronagraph

A miniature 1-m focal length coronagraph has been constructed at NSO/SP, based on a 5-cm diam superpolished silicon mirror from Zeiss, F.R.G. The optical configuration is simply off-axis reflection from the objective to an occulting disk, Lyot stop, and secondary optics. The coronagraph has been designed to be used either with photographic recording or a video CCD camera, both in combination with a VARO image tube. Details of the design and preliminary results are presented. It is shown that a mirror-objective-based coronagraph has many advantages and few disadvantages compared with the traditional singlet-objective-lens Lyot coronagraph. This reflecting coronagraph design is shown to be appropriate for larger systems, using other types of mirror substrate, with the prospect of very small net instrumental polarization, of crucial importance for certain coronal studies, with excellent aberration correction over modest fields.