Catalyzes the conversion of the ubiquitous 5,6-epoxycarotenoids, antheraxanthin and violaxanthin, into capsanthin and capsorubin, respectively. all-trans-violaxanthin = all-trans-capsorubin all-trans-antheraxanthin = all-trans-capsanthin Carotenoid biosynthesis; capsanthin biosynthesis; capsanthin from antheraxanthin: step 1/1. Carotenoid biosynthesis; capsorubin biosynthesis; capsorubin from violaxanthin: step 1/1. Belongs to the lycopene cyclase family.