| 摘要 |
PROBLEM TO BE SOLVED: To provide a small-sized telephoto lens with a long back focus which has a 10 to 20 deg. field angle and an F number of about 2.8 and which is suitable for an electronic camera, a video camera, etc. SOLUTION: The telephoto lens has a 1st lens group G1 which comprises at least two positive lenses and at least two negative lenses and has negative refracting power as the whole or weak refracting power meeting condition (1) and a 2nd lens group G2 which is composed of a lens group including a cemented lens of a negative and a positive lens and at least one positive lens following it and has positive refracting power on the whole and the air- converted length bkf of the interval from the most image-side surface with optical power to an image plane is >=45 mm. Here, (1) 0.1<fT/|f1|<0.5, where fT and f1 are the focal lengths of the whole lens system and 1st lens group G1.
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