Patent attributes
To provide an endoscope objective lens which has a lens constitution of a relatively small number of three pieces, a short total length of lens, and various kinds of good optical performances starting with curvature of field. It is constituted of a first lens L1 directing its concave surface to the image side, a second lens L2 made of a positive meniscus lens directing its convex surface to the image side, and a third lens L3 made of a planoconvex lens directing its convex surface to the object side arranged sequentially from the object side, and a stop placed between said first lens L1 and said second lens L2. It also satisfies the following Conditional Expressions:2.00<|f1/f|<3.00, (1)0.50<|f2/f3|<0.70, (2)2.00<|f1/d1-2|<5.00 , (3)0.40<|R2R/R2F|<0.60 . (4)Note that f is the focal length of the whole system, f1–f3 the focal lengths of the first-third lenses, respectively, d1-2 the air distance between the first lens and the second lens, R2F the radius of curvature of the object-side surface of the second lens, and R2R the radius of curvature of the image-side surface of the second lens.
