When combined with a lens formed of an ultra-low dispersion glass, a lens formed of a high-refractivity low-dispersion glass enables the downsizing of an optical system while correcting chromatic aberration. It hence occupies a very important place as an optical element to constitute an image-sensing optical system or a projection optical system such as a projector.
Patent Document 1 discloses such a high-refractivity low-dispersion glass.