| 摘要 |
PURPOSE:To attain a back focus >=1.7 times as long as the focal length of a high-aperture ratio wide-angle lens by constituting the lens with three groups of lenses satisfying specific conditions and limiting focal lengths of individual lenses and lens groups. CONSTITUTION:The lens system consists of the first lens group which consists of the first positive lens and the second the third negative meniscus lenses and has a negative refracting power as the whole, the second lens group which consists of one or two lenses and has a positive refracting power as the whole, and the third lens group which consists of two or three lens groups consisting of three - five lenses including a negative lens and has a positive refractive index as the whole. The lens system has >=1.7f back focus when the focal length of the whole of the system is denoted as (f), and conditions indicated by formulas are satisfied. |
