Compact wide-angle zoom lens

• US 5,864,435 A
• Filed: 10/07/1997
• Issued: 01/26/1999
• Est. Priority Date: 11/19/1996
• Status: Expired due to Fees

• Current Assignee: Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Inventors: Toyama, Nobuaki
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US08/946,072
• Time in Patent Office: 476 Days
• Field of Search: 359/691, 359/692, 359/717, 359/795
• US Class Current: 359/692
• CPC Class Codes: G02B 13/02 Telephoto objectives, i.e. systems of the type + - in which the distance from the front vertex to the image plane is less than the equivalent focal length
• CPC Class Codes: G02B 15/142 having two groups only
• CPC Class Codes: G02B 15/1421 the first group being positive

Abstract

In a compact wide-angle zoom lens having a two-group configuration composed of positive and negative lens groups, each lens is set to have a predetermined form and satisfy a predetermined range of conditional expression, thereby attaining a high brightness at its wide-angle end, a large angle of view, and a small lens thickness at its telephoto end. The first lens group comprises a biconcave negative first lens L₁ ; a cemented lens composed of a negative second lens L₂ and a biconvex positive third lens L₃ ; and a biconvex positive fourth lens L₄. The second lens group comprises a fifth lens L₅ having an aspheric surface; a sixth lens L₆ having a positive meniscus form with a convex surface directed onto the image side; and a seventh lens L₇ having a negative meniscus form with a convex surface directed onto the image side. The zoom lens further satisfies the following conditional expressions:

0<(r.sub.3 +r.sub.4)/(r.sub.3 -r.sub.4)<3.5, 0.5<(r.sub.11

+r₁₂)/(r₁₁ -r₁₂) <4.5, 0.9<|r₅ /r₄ |<2.3,n₁ >1.65, n₄ <1.57

wherein

r₃ is the radius of curvature of the object-side surface of said second lens

r₄ is the radius of curvature of the image-side surface of said second lens

r₅ is the radius of curvature of the image-side surface of said third lens

r₁₁ is the radius of curvature of the object-side surface of said sixth lens

r₁₂ is the radius of curvature of the image-side surface of said sixth lens

n₁ is the refractive index of said first lense

n₄ is the refractive index of said fourth lense

Claims

1. A compact wide-angle zoom lens comprising, successively from an object side, a first lens group having a positive refracting power and a second lens group having a negative refracting power, in which a distance between said lens groups is changed to attain a variable power;

wherein said first lens group comprises, successively from the object side, a biconcave negative first lens, a negative second lens, a biconvex positive third lens, and a biconvex positive fourth lens, said second and third lenses being cemented together;

wherein said second lens group comprises, successively from the object side, a fifth lens having at least one aspheric surface, a sixth lens having a positive meniscus form with a convex surface directed onto an image side, and a seventh lens having a negative meniscus form with a convex surface directed onto the image side; and

wherein said zoom lens satisfies the following conditional expressions;

space="preserve" listing-type="equation">0<

(r.sub.3 +r.sub.4)/(r.sub.3 -r.sub.4)<

3.5 (1)

space="preserve" listing-type="equation">0.5<

(r.sub.11 +r.sub.12)/(r.sub.11 -r.sub.12)<

4.5 (2)

space="preserve" listing-type="equation">0.9<

|r.sub.5 /r.sub.4 |<

2.3 (3)

space="preserve" listing-type="equation">n.sub.1 >

1.65 (4)

space="preserve" listing-type="equation">n.sub.4 <

1.57 (5)

wherein

r₃ is the radius of curvature of the object-side surface of said second lens

r₄ is the radius of curvature of the image-side surface of said second lens

r₅ is the radius of curvature of the image-side surface of said third lens

r₁₁ is the radius of curvature of the object-side surface of said sixth lens

r₁₂ is the radius of curvature of the image-side surface of said sixth lens

n₁ is the refractive index of said first lens

n₄ is the refractive index of said fourth lens.

2. A compact wide-angle zoom lens according to claim 1, wherein said first lens has at least one aspheric surface.

3. A compact wide-angle zoom lens according to claim 1, wherein said fifth lens is made of a plastic material.