F-theta lens
AssigneeFuji Photo Optical Co., Ltd.
InventorYoko Nakai
Life of this patent
Estimating the term…
Abstract
An fθ lens comprises, successively from the luminous flux entrance side, a first lens made of a negative lens having a flat surface on one side, a positive second lens having a surface with a stronger curvature directed onto the image side, and a third lens made of a negative meniscus lens cemented to the second lens; and satisfies the following conditional expressions (1) to (3): −2.2<f1/f<−1.7 (1) 0.35<f2/f (2) 2.21<N3+0.0176ν3<2.27 (3) where f is the composite focal length of the whole lens system, f1 is the focal length of first lens, f2 is the focal length of second lens, N3 is the refractive index of third lens at d-line, and ν3 is the Abbe number of third lens at d-line.
Claims4
An fθ lens comprising, successively from a luminous flux entrance side, a first lens made of a negative lens having a flat surface on one side, a second lens made of a positive lens having a surface with a stronger curvature directed onto an image side, and a third lens made of a negative meniscus lens, said second and third lenses being cemented together;
- said fθ lens satisfying the following conditional expressions (1) to (3):
- −2.2<f1/f<−1.7 (1)
- 0.35<f2/f (2)
- 2.21<N3+0.0176ν3<2.27 (3)
- where
- f is the composite focal length of the whole lens system;
- f1 is the focal length of first lens;
- f2 is the focal length of second lens;
- N3 is the refractive index of third lens at d-line;
- and
- ν3 is the Abbe number of third lens at d-line.
Dependencies are inferred from the claim text.