Telephoto lens system
AssigneePENTAX Corporation
InventorsJunichi Fujisaki, Takayuki Ito
Life of this patent
Estimating the term…
Abstract
A telephoto lens system of a four-lens-group arrangement includes a negative first lens group, a positive or negative second lens group, a negative third lens group and a positive fourth lens group. The telephoto lens system of the four-lens-group arrangement is constituted by less than six lens elements in total. The positive or negative second lens group is constituted by a positive lens element and a negative lens element which are cemented to each other, in this order from the object. The positive lens element has a convex surface with a larger curvature facing toward the object. The positive or negative second lens group satisfies the following condition: 0.8<f2p/|f2n|<1.4. (1)
Claims11
A telephoto lens system of at least a four-lens-group arrangement comprises a positive first lens group, a positive or negative second lens group, a negative third lens group and a positive fourth lens group, in this order from an object,
- wherein said telephoto lens system of the at least four-lens-group arrangement comprises six lens elements or less in total;
- wherein said positive or negative second lens group comprises a positive lens element and a negative lens element that are cemented to each other, in this order from the object;
- wherein said positive lens element has a convex surface facing toward the object side, said convex surface having a larger curvature than a surface of the positive lens element facing toward the image side;
- wherein said positive or negative second lens group satisfies the following condition:
- 0.8<f2p/|f2n|<1.4
- wherein
- f2p designates the focal length of said positive lens element of said second lens group;
- and
- f2n designates the focal length of said negative lens element of said second lens group;
- and
- wherein the telephoto lens system satisfies the following conditions:
- 80<ν2p
- 20<ν2p−ν2n<60
- wherein
- ν2p designates the Abbe number of said positive lens element of said positive or negative second lens group;
- and
- ν2n designates the Abbe number of said negative lens element of said positive or negative second lens group.
A telephoto lens system of at least a four-lens-group arrangement comprises a positive first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in this order from an object,
- wherein said telephoto lens system of the at least four-lens-group arrangement comprises six lens elements or less in total;
- wherein said positive second lens group comprises a negative meniscus lens element and a positive lens element that are cemented to each other, in this order from the object;
- wherein said negative meniscus lens element has the a convex surface facing toward the object side, and the positive lens element has a convex surface facing toward the object side, said convex surface of the positive lens element having a larger curvature than a surface of the positive lens element facing toward the image side;
- wherein said positive second lens group satisfies the following condition:
- 0.4<f2p/|f2n|<0.8
- wherein
- f2p designates the focal length of said positive lens element of said second lens group;
- and
- f2n designates the focal length of said negative lens element of said second lens group;
- and
- wherein the telephoto lens system satisfies the following conditions:
- 70<ν2p
- 20<ν2p−ν2n<60
- wherein
- ν2p designates the Abbe number of said positive lens element of said positive second lens group;
- and
- ν2n designates the Abbe number of said negative lens element of said positive second lens group.
A telephoto lens system of at least a four-lens-group arrangement comprises a positive first lens group, a positive or negative second lens group, a negative third lens group and a positive fourth lens group, in this order from the object,
- wherein said telephoto lens system of the at least four-lens-group arrangement comprises six lens elements or less in total;
- wherein said positive or negative second lens group comprises a positive lens element and a negative lens element that are cemented to each other in this order from the object, or comprises a negative lens element and a positive lens element that are cemented to each other in this order from the object;
- wherein said positive or negative second lens group satisfies the following condition:
- 70<ν2p
- 20<ν2p−ν2n<60
- wherein
- ν2p designates the Abbe number of said positive lens element of said positive or negative second lens group;
- and
- ν2n designates the Abbe number of said negative lens element of said positive or negative second lens group;
- and
- wherein the telephoto lens system satisfies the following condition:
- 0.15<Dp/f<0.5
- wherein
- Dp designates the sum of the thickness of said positive first lens group and that of said positive or negative second lens group;
- and
- f designates the focal length of said telephoto lens system.
Dependencies are inferred from the claim text.