| 摘要 |
A photo-taking lens of a two-unit, five element construction for an underwater camera comprises, in succession from the object side, a fixed forward unit having a first element having a meniscus lens having its convex surface facing the object side and having a negative refractive power when the medium on the object side is water, and a rearward unit having a positive second element having a biconvex positive lens, a negative third element having a biconcave negative lens, a positive fourth element having a positive meniscus lens having its convex surface facing the image side, and a positive fifth element having a positive lens having its surface of sharper curvature facing the image side, and movable as a whole along the optic axis for focussing. The photo-taking lens satisfies the following condition: 0.75f<r2<2f, where f is the rearward focal length of the entire system during focusing at infinity when the medium on the object side is water, and r2 is the radius of curvature of that surface of the first element which is adjacent to the image side.
|
