Photographic small size objective
AssigneeCanon Kabushiki Kaisha
InventorKeiji Ikemori
Life of this patent
Estimating the term…
Abstract
A photographic small size objective of the modified Gauss type which is well corrected for high grade imaging performance. The objective comprises, from front to rear, a first lens in a meniscus form of positive power with its convex curvature toward the front, a second lens in a similar form, a third lens in a meniscus form of negative power with its convex curvature toward the front, a fourth lens in a meniscus form of negative power with its convex curvature toward the rear, and a fifth lens of positive power with its rear surface having a strong refractive power.
Claims2
A photographic objective of small size consisting of five lens groups, each group having a single lens, including, from front to rear,
- a meniscus 1st lens of positive power convex toward the front;
- a meniscus 2nd lens of positive power convex toward the front;
- a meniscus 3rd lens of negative power convex toward the front;
- a meniscus 4th lens of negative power convex toward the rear;
- and
- a 5th lens of positive power with its rear surface having a strong refractive power, and satisfying the following conditions:
- 0. 04<D.sub.4 /f<0.06 (1)
- 21.2.ltoreq..nu.2-.nu.3<28 (2)
- 0.29<.vertline..psi.1.vertline..multidot.f<0.75, .psi.1<0 (3)
- where:
- f is the focal length of the entire system;
- Ni and .nu.i are the refractive index and Abbe number of the i-th lens counting from the front respectively;
- Di is the i-th lens thickness or air separation counting from the front;
- Ri is the radius of curvature of the i-th lens surface counting from the front;
- and
- .psi.1=(1-N2)/R.sub.4 +(N3-1)/R.sub.5.
A photographic objective of small size consisting of five lens groups, each group having a single lens including, from front to rear,
- a meniscus 1st lens of positive power convex toward the front;
- a meniscus 2nd lens of positive power convex toward the front;
- a meniscus 3rd lens of negative power convex toward the front;
- a meniscus 4th lens of negative power convex toward the rear;
- and
- a 5th lens of positive power with its rear surface having a strong refractive power, and satisfying the following conditions:
- 0.04<D.sub.4 /f<0.06 (1)
- 21.2.ltoreq..nu.2-.nu.3<28 (2)
- 0.29<.vertline..psi.1.vertline..multidot.f<0.75, .psi.1<0 (3)
- 1.72<(N1+N2+N5)/3<1.81 (4)
- 6.7<(1/R.sub.6 +1/.vertline.R.sub.7 .vertline.)f<8 (5)
- 0.045<D.sub.7 /f<0.082 (6)
- 20<.nu.3<28, 1.75<N3<1.93 (7)
- 46<.nu.5<60 (8)
- where:
- f is the focal length of the entire system;
- Ni and .nu.i are the refractive index and Abbe number of the i-th lens counting from the front respectively;
- Di is the i-th lens thickness or air separation counting from the front;
- Ri is the radius of curvature of the i-th lens surface counting from the front;
- and
- .psi.1=(1-N2)/R4+(N3-1)/R5.
Dependencies are inferred from the claim text.