| 摘要 |
PURPOSE:To permit the easy conversion of a focal length and to obtain a substantial variable power ratio of >=1.5 times by constituting a titled lens, successively from the main lens system side, of the 1st positive lens, the 2nd negative lens and the lens component combined with the 3rd positive lens and the 4th negative lens, having negative refracting power as a whole and satisfying the specific conditions. CONSTITUTION:This lens system is freely removably disposed behind the main lens system and converts the focal length of the entire lens system when inserted and removed. The lens system is constituted, successively from the main lens side, of the 1st positive lens, the 2nd negative lens and the lens component combined with the 3rd positive lens and the 4th negative lens and has the negative refracting power as a whole. The lens system satisfies the conditions expressed by equations (where R2 is the radius of curvature of the image side face of the 1st positive lens, R3, R4 are respectively the radii of curvature on the main lens side and image side faces of the 2nd negative lens, R5 is the radius of curvature of the main lens system side face of the 3rd positive lens, N1, N2, N3;, N4 are respectively the refractive indices of the 1st positive lens, the 2nd negative lens, the 3rd positive lens and the 4th negative lens). |
