For example, Patent Literature 1 discloses an optical glass that has a refractive index of 1.70 to 1.82 and an Abbe number of 40 to 55. It is possible to use such an optical glass as a lens of an optical device such as a camera or a microscope.
Now, in optical systems in optical devices such as a camera or a microscope, in order to correct the chromatic aberrations of lens in the visible range, ordinary optical glass is used in combination with optical glass that differs in partial dispersion ratio from the ordinary optical glass (has anomalous dispersibility). On the other hand, in recent years, microscopic observations with the use of light in the near-infrared range, including multiphoton microscope (multiphoton microscope), and the like have been also being made, and there is an increasing need for optical glass capable of correcting chromatic aberrations at wavelengths not only in the visible range but also in the near-infrared range.