Variable magnification optical zoom lens system

• US 6,124,984 A
• Filed: 12/12/1997
• Issued: 09/26/2000
• Est. Priority Date: 12/13/1996
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Ohshita, Koichi, Shibayama, Atsushi
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): SCHWARTZ, JORDAN MARC
• Application Number:
  US08/990,063
• Time in Patent Office: 1,019 Days
• Field of Search: 359/680-682, 359/683, 359/687, 359/689, 359/676, 359/708, 359/713-716, 359/686
• US Class Current: 359/689
• CPC Class Codes: G02B 15/143507 arranged -++
• CPC Class Codes: G02B 15/177 having a negative front lens or group of lenses

Abstract

A variable magnification zoom lens system comprising: in order from the object side, a first lens group having a negative refractive power and a focal length f1; a second lens group having a positive refractive power; and a third lens group having a positive refractive power and a focal length f3 with the first and second lens group arranged to be driven together such that when zooming is performed from the maximum wide-angle state to the maximum telephoto state of the zoom lens system, the first lens group and the second lens group move such that the distance between the first lens group and the second lens group is decreased, and at the same time, the distance between second lens group and the third lens group is increased and with the following condition being fulfilled: 0.4<f3/|f1|<0.8.

Claims

1. A variable magnification zoom lens system having an optical axis comprising, in order from an object side,

a first lens group consisting of two negative lenses and a positive lens and having an overall negative refractive power;

a second lens group having a positive refractive power; and

a third lens group, which is fixed along the optical axis and overall has a positive refractive power;

with the first and second lens group arranged to be driven such that when zooming from a maximum wide-angle state to a maximum telephoto state, the distance between said first lens group and said second lens group is reduced, and at the same time, the distance between said second lens group and said third lens group is increased; and

the following conditions are fulfilled;

space="preserve" listing-type="equation">0.7<

f2/|f1|<

1.5

space="preserve" listing-type="equation">3<

f3/fw<

10

wherein;

f1 is;

the focal length of said first lens group;

f2 is;

the focal length of said second lens group;

f3 is;

the focal length of said third lens group; and

fW is;

an overall focal length of said zoom lens system in the maximum wide-angle state wherein said first lens group consists of, in order from the object side,

a negative meniscus lens having a convex surface facing toward the object side; and

a cemented lens made up of a bi-concave negative lens and a positive meniscus lens with said positive meniscus lens having a convex surface facing toward the object side.

2. The zoom lens system of claim 1 wherein the following conditions are fulfilled:

space="preserve" listing-type="equation">30<

ν

1<

40 and

space="preserve" listing-type="equation">0.25<

n3-n2

wherein;

ν

1 is;

Abbe number of said negative meniscus lens;

n2 is;

the refractive index on the d-line of said bi-concave lens;

n3 is;

the refractive index on the d-line of said positive meniscus lens.

3. The zoom lens system of claim 1 wherein said second lens group comprises:

in order from the object side,

two positive lenses;

one negative lens, and

one positive lens.

4. The zoom lens system of claim 2 wherein said second lens group comprises:

in order from the object side;

two positive lenses;

one negative lens; and

one positive lens.

5. The zoom lens system of claim 1 wherein said second lens group comprises:

in order from the object side,

two positive lenses;

one negative lens; and

two positive lenses.

6. The zoom lens system of claim 2 wherein said second lens group comprises:

in order from the object side,

two positive lenses;

one negative lens; and

two positive lenses.

7. The zoom lens system of claim 1 wherein said third lens group comprises one positive single lens having at least one aspherical surface.

8. The zoom lens system of claim 7 wherein said positive single lens is bi-convex;

and an image side surface of said positive single lens is aspherical such that the positive refractive power is reduced from the optical axis toward the periphery.

9. A variable magnification zoom lens system having an optical axis comprising, in order from an object side,

a first lens group consisting of two negative lenses and a positive lens and having an overall negative refractive power;

a second lens group having a positive refractive power; and

a third lens group, which is fixed along the optical axis and overall has a positive refractive power;

with the first and second lens group arranged to be driven such that when zooming from a maximum wide-angle state to a maximum telephoto state, the distance between said first lens group and second lens group is reduced, and at the same time, the distance between said second lens group and said third lens group is increased; and

the following conditions are fulfilled;

space="preserve" listing-type="equation">0.7<

f2/|f1|<

1.5

space="preserve" listing-type="equation">3<

f3/fw<

10

wherein;

f1 is;

the focal length of said first lens group;

f2 is;

the focal length of said second lens group;

f3 is;

the focal length of said third lens group; and

fW is;

an overall focal length of said zoom lens system in the maximum wide-angle state and wherein said third lens group comprises one positive single lens having at least one aspherical surface wherein said positive single lens is bi-convex; and

an image side surface of said positive single lens is aspherical such that said positive refractive power is reduced from the optical axis toward the periphery.