Abstract
The development of balloon and rocket vehicles provides opportunity for nearly continuous observation of those parts of the solar corona remote from the sun. This opportunity places new requirements on the freedom of the coronagraph from scattered light. Several possible means of improving the coronagraph are described. It is found that the available optical media do not permit a significant reduction in the scattered light in the ordinary coronagraph. The reflecting coronagraph and the simple, externally occulted coronagraph can be made freer of scattered light by from one to more than two orders of magnitude, respectively, than the Lyot coronagraph. The use of the apodized, external, occulting disk developed by several investigators can reduce the scattered light by at least three orders of magnitude so that the instrumental background is similar to the skylight encountered during total eclipse.
© 1963 Optical Society of America
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