Claims
- 1. A zoom lens comprising:
- three lens groups,
- said three lens groups including, from front to rear, a first lens group of positive refractive power, a second lens group of negative refractive power and a third lens group,
- said first lens group consisting of, from front to rear, a bi-convex first lens, a second lens of negative refractive power, and a third lens of positive refractive power, whereby zooming is effected by changing the air separations between the first lens group and the second lens group and between the second lens group and the third lens group of said three lens groups, the three lenses of said first lens group being separated from each other and a first lens surface of said second lens being concave toward the object.
- 2. A zoom lens according to claim 1, satisfying the following conditions:
- 0.5f3<f1<2f3
- 0.8.vertline.R2.vertline.<R3.vertline.<1.5R2
- wherein
- F1 is the focal length of said first lens groups;
- f1, and f3 are the focal lengths of said first and said third lenses respectively; and
- Ri is the radius of curvature of the i-th surface counting from front in said first lens group.
- 3. A zoom lens according to claim 2, wherein said second lens is made of plastic.
- 4. A zoom lens according to claim 1, wherein said first lens is made of optical glass, and said third lens is made of plastic.
- 5. A zoom lens according to claim 1, wherein at least one of the lens surfaces in said first lens group is aspherical.
- 6. A zoom lens comprising:
- a front lens unit of positive power including:
- a first lens convex on both sides, a second negative lens with its first surface concave toward the object, and a third positive lens, the lenses of said front lens unit being separated from each other;
- a middle lens unit of negative power;
- a rear lens unit;
- wherein the zooming is performed by simultaneously changing the axial space between the front lens unit and the middle lens and the axial space between the middle lens unit and the rear lens unit;
- and satisfying the following conditions:
- 0. 5f3<f1<2f3
- 0.8.vertline.R2.vertline.<.vertline.R3.vertline.<.vertline.1.5.vertline.R2.vertline.
- wherein f1 represents the focal length of said first lens, f3 represents the focal length of said third lens, R3 represents the curvature on the image side of the said first lens, and R2 represents the radius of curvature on the object side of said second lens.
- 7. A zoom lens according to claim 6, in which said second lens and said third lens are made of plastics.
- 8. A zoom lens according to claim 7, in which one surface of said second lens and said third lens each have one aspherical surface.
- 9. A zoom lens comprising:
- a front lens unit of positive power consisting of a bi-convex first lens, a bi-concave second lens and third lens convex toward the object, the lenses of said front lens unit being separated from each other; a middle lens unit of negative power, and a rear lens unit, wherein zooming is performed by simultaneously changing the axial space between said front lens unit and said middle lens unit and the axial space between said middle lens unit and said rear lens unit, and
- said first lens is made of optical glass, said second and third lenses are made of plastic, and the radius of curvature on the image side of said second lens is larger than that on the object side of said third lens.
- 10. A zoom lens according to claim 9, which satisfies the following conditions:
- 0.5f3<f1<2f3
- 0.8.vertline.R2.vertline.<.vertline.R3.vertline.<1.5.vertline.R2.vertline.
- wherein f1 represents the focal length of said first lens, f3 represents the focal length of said third lens, R2 represents the radius of curvature on the image side of said first lens and R3 represents the radius of curvature on the object side of said second lens.
Priority Claims (1)
Number |
Date |
Country |
Kind |
57-123606 |
Jul 1982 |
JPX |
|
Parent Case Info
This is a continuation of application Ser. No. 511,674, filed July 7, 1983 now abandoned.
US Referenced Citations (3)
Continuations (1)
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Number |
Date |
Country |
Parent |
511674 |
Jul 1983 |
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