This is a high-performance telephoto lens utilizing new optical glass with a low refractive index, low dispersion and anomalous dispersion. The special dispersion of the new optical glass is used to effectively compensate for chromatic aberration, offering excellent images at maximum aperture of the large aperture. Furthermore, by reducing the telephoto ratio taking advantage of the characteristic of a low refractive index and the adoption of a rear focusing system, the lens is made lightweight and compact despite being super telephoto, in addition to offering high operability.