Zoom lens system
AssigneePENTAX Corporation
InventorMasaru Eguchi
Life of this patent
Estimating the term…
Abstract
A zoom lens system includes a positive first lens group, a positive second lens group, a diaphragm, and a negative third lens group. The first through third lens groups move in an optical axis direction for zooming. The positive first lens group includes a negative lens element, and at least one positive lens element. The negative lens element is positioned at the most object-side of the positive first lens group, and is provided with a concave surface on the object-side surface thereof. The zoom lens system satisfies a number of specified conditions.
Claims13
A zoom lens system comprising a positive first lens group, a positive second lens group, a diaphragm, and a negative third lens group, in this order from an object,
- wherein each of said first through third lens groups move in an optical axis direction to perform zooming;
- wherein said positive first lens group comprises a negative lens element, and at least one positive lens element;
- wherein said negative lens element is positioned at the most object-side of said positive first lens group, and is provided with a concave surface on the object-side surface of said negative lens element;
- and
- wherein said zoom lens system satisfies the following conditions:
- −0.85<r1/fW<−0.5
- 45<νp−νn
- 0.05<LD2/fT<0.09
- wherein
- r1 designates the radius of curvature of the object-side surface of the negative lens element in said positive first lens group;
- fW designates the focal length of the entire zoom lens system at the short focal length extremity;
- fT designates the focal length of the entire zoom lens system at the long focal length extremity;
- νp designates the average Abbe number of said positive lens element in said positive first lens group;
- νn designates the average Abbe number of said negative lens element in said positive first lens group;
- and
- LD2 designates the distance, along the optical axis in the positive second lens group, from the most object-side surface thereof to the most image-side surface thereof.
A zoom lens system comprising a positive first lens group, a positive second lens group, a diaphragm, and a negative third lens group, in this order from an object, wherein each of said first through third lens groups move in an optical axis direction to perform zooming;
- wherein said positive first lens group comprises a negative lens element, and at least one positive lens element;
- wherein said negative lens element is positioned at the most object-side of said positive first lens group, and is provided with a concave surface on the object-side surface of said negative lens element;
- and
- wherein said zoom lens system satisfies the following conditions:
- −0.811≦r1/fW<−0.5
- 45<νp−νn
- 0.05<LD2/fT<0.09
- wherein
- r1 designates the radius of curvature of the object-side surface of the negative lens element in said positive first lens group;
- fW designates the focal length of the entire zoom lens system at the short focal length extremity;
- fT designates the focal length of the entire zoom lens system at the long focal length extremity;
- νp designates the average Abbe number of said positive lens element in said positive first lens group;
- νn designates the average Abbe number of said negative lens element in said positive first lens group;
- and
- LD2 designates the distance, along the optical axis in the positive second lens group, from the most object-side surface thereof to the most image-side surface thereof.
Dependencies are inferred from the claim text.