Study on test the large aperture flat by a smaller standard mirror use the Ritchey-Common method

Use a large aperture spherical surface as a standard mirror to test the large aperture plane mirror have been wildly studied, but most research restrain on the situation that the aperture of the standard mirror is larger than the flat. Sometimes we may not have such a large spherical mirror, and how to use a smaller standard mirror to test a large aperture flat is eager to be researched. Based on the principle of the Ritchey-Common testing method, accorded to the situation above, then analyzed the relationship between the Ritchey angle, the mirror's diameter and the mirror spacing, finally deduced the relationship equation, that result can be well used in the testing of the large aperture flat.