Superwide-angle lens system

• US 8,659,841 B2
• Filed: 08/09/2012
• Issued: 02/25/2014
• Est. Priority Date: 08/11/2011
• Status: Active Grant

• Current Assignee: PENTAX RICOH IMAGING COMPANY, LTD.
• Original Assignee: Pentax Ricoh Imaging Americas Corporation (Ricoh Company Limited)
• Inventors: Enomoto, Takashi
• Primary Examiner(s): Spector, David N
• Application Number:
  US13/570,389
• Publication Number:
  US 20130038950A1
• Time in Patent Office: 565 Days
• Field of Search: 359/749, 359/752, 359/753, 359/793
• US Class Current: 359/753
• CPC Class Codes: G02B 13/06 Panoramic objectives; So-called "sky lenses" including panoramic objectives having reflecting surfaces

Abstract

A superwide-angle lens system includes a negative first lens group, an aperture diaphragm, and a positive second lens group. The first lens group includes two negative meniscus lens elements, and a positive lens element. The second lens group includes a cemented lens having negative and positive lens elements; and a positive lens element. The following conditions (1) and (2) are satisfied:
−1.45<f12/f<−1.15  (1)
1.4<SF2<2.4  (2)

• • f12: the combined focal length of the two the negative meniscus lens elements in the first lens group,
  • f: the focal length of the lens system,
  • SF2: the shaping factor of the negative meniscus lens element on the image side in the first lens group.

Claims

1. A superwide-angle lens system comprising a negative first lens group, an aperture diaphragm, and a positive second lens group, in that order from the object side,

wherein said first lens group is provided with a negative meniscus lens element having a convex surface on the object side, a negative meniscus lens element having a convex surface on the object side, and a positive lens element, in that order from the object side,

wherein said second lens group is provided with a cemented lens having a negative lens element and a positive lens element;

and a positive lens element, in that order from the object side, and

wherein the following conditions (1) and (2) are satisfied;

−

1.45<

f12/f<

−

1.15 

 

(1), and

1.4<

SF2<

2.4 

 

(2), wherein

f12 designates the combined focal length of the two said negative meniscus lens elements provided in said first lens group,

f designates the focal length of the entire said superwide-angle lens system,

SF2 designates the shaping factor of the negative meniscus lens element provided on the image side of the two said negative meniscus lens elements provided in said first lens group,

SF2=(r21+r22)/(r21−

r22),

r21 designates the radius of curvature of the surface on the object side of said negative meniscus lens element provided on the image side, and

r22 designates the radius of curvature of the surface on the image side of said negative meniscus lens element provided on the image side.

2. The superwide-angle lens system according to claim 1, wherein the following condition (3) is satisfied:

1.75<

nd1 

 

(3), wherein

nd1 designates the refractive index at the d-line of the negative meniscus lens element provided on the object side of the two said negative meniscus lens elements.

3. The superwide-angle lens system according to claim 1, wherein the following condition (4) is satisfied:

−

0.5<

SF6<

0.1 

 

(4), wherein

SF6 designates the shaping factor of the positive lens element provided on the image side of said second lens group,

SF6=(r61+r62)/(r61−

r62),

r61 designates the radius of curvature of the surface on the object side of said positive lens element provided on the image side of said second lens group, and

r62 designates the radius of curvature of the surface on the image side of said positive lens element provided on the image side of said second lens group.

4. The superwide-angle lens system according to claim 1, wherein the following condition (5) is satisfied:

0.9<

fG1/fG2<

1.8 

 

(5), wherein

fG1 designates the focal length of said first lens group, and

fG2 designates the focal length of said second lens group.

5. The superwide-angle lens system according to claim 1, wherein said superwide-angle lens system comprises a fisheye lens system.