TELEPHOTO LENS UNIT

PROBLEM TO BE SOLVED: To provide a telephoto lens unit usable as an interchangeable lens for telephotography and also usable as a ground telescope.SOLUTION: A telephoto lens unit 1 having a lens barrel which supports a telephoto lens and being attachable/detachable with respect to a camera body 16 is so configured that the lens barrel includes, when the object side of the lens barrel is defined as the front side, a front lens barrel section 11 which supports the telephoto lens, and a rear lens barrel section 13 which is attachable/detachable with respect to the front lens barrel section. A distance from the surface of the telephoto lens, which is located on the side closest to the image side, to the image forming surface of the telephoto lens is set sufficiently long, and converter lens units 12 and 14 for elongating and shortening focal lengths, are mounted on the front lens barrel section 11 in place of the rear lens barrel section 13 to provide interchangeable telephoto lenses for a camera which have different focal lengths. Furthermore, the telephoto lens can be used as a ground telescope by connecting an erect prism unit 15 and an eyepiece lens unit 17 to the front lens barrel section 11 in place of the rear lens barrel section.