Image forming lens, camera device, and handheld terminal
An image forming lens including an aperture stop, a first lens group arranged on the object side relative to the aperture stop, and a second lens group having a positive power arranged on an image side relative to the aperture stop, the first lens group including a first F lens group having a negative power and a first R lens group having a positive power arranged in this sequence from the object side with the widest air space between the first F lens group and the first R lens group, the first F lens group including at least two negative lenses, the first R lens group including at least one positive lens, the second lens group including a second F lens group having a positive power and a second R lens group arranged in this sequence from the object side, the second F lens group including a first positive lens, a first negative lens, a second negative lens, and a second positive lens arranged in this sequence from the object side, and the second R lens group including at least one lens.
1. A fixed focal length image forming lens comprising:
an aperture stop;
a first lens group arranged on an object side relative to the aperture stop; and
a second lens group having a positive power arranged on an image side relative to the aperture stop,
the first lens group comprising a first F lens group having a negative power and a first R lens group having a positive power arranged in this sequence from the object side with a widest air space within the first lens group between the first F lens group and the first R lens group, the first F lens group comprising at least two negative lenses, the first R lens group comprising at least one positive lens,
the second lens group comprising a second F lens group having a positive power and a second R lens group arranged in this sequence from the object side, the second F lens group comprising a first positive lens, a first negative lens, a second negative lens, and a second positive lens arranged in this sequence from the object side,
wherein the second R lens group comprises one aspheric surface having a form of decreasing positive power from an optical axis of the second R lens group toward a periphery thereof,
a focal length f 2 F of the second F lens group and a focal length f 2 R of the second R lens group satisfy the following relationship (1):
0.4 <f 2 F/f 2 R< 0.6 (1),
and the aspheric surface of the second R lens group satisfies the following relationship (2):
0.3 <D 1/ D 2<0.5 (2),
where D 2 represents a sag amount of the aspheric surface and a surface formed by a paraxial curvature radius at a position of an effective height of H2R of beams of light of the aspheric surface and D 1 represents a sag amount of the aspheric surface and a surface formed by a paraxial curvature radius at a position of 0.8×H2R.
2. The image forming lens according to claim 1 , wherein a thickness D 2 F_ 2 R between the most object side surface of the second F lens group on the object side, the most image side surface of the second R lens group on the image side, and a maximum image height Y′ satisfy the following relationship (3):
1.5 <D 2 F — 2 R/Y′< 3.0 (3).
3. The image forming lens according to claim 1 , wherein the first F lens group comprises an aspheric surface having a form of decreasing negative power from an optical axis of the first F lens group toward a periphery thereof, and the aspheric surface of the second R lens group satisfies the following relationship (4):
0.1 <D 3/ D 4<0.3 (4),
where D 3 represents a sag amount of the aspheric surface and a surface formed by a paraxial curvature radius at a position of 0.7×H1F where H1F represents an effective height of beams of light of the aspheric surface and D 4 represents a sag amount of the aspheric surface and a surface formed by a paraxial curvature radius at a position of 0.9×H1F.
4. The image forming lens according to claim 1 , wherein the second R lens group consists of one aspheric lens.
5. The image forming lens according to claim 1 , wherein the aspheric lens of the second R lens group comprises a material having an Abbe number vd satisfying the following relationship (5):
60 <νd< 96 (5).
6. The image forming lens according to claim 1 ,
wherein the first F lens group comprises two negative lenses, the first R lens group comprises one positive lens, and the second negative lens of the first F lens group from the object side has an aspheric surface on the image side having a form of decreasing negative power from an optical axis of the first F lens group toward a periphery thereof,
wherein the first positive lens and the first negative lens in the second F lens group are cemented and the second negative lens and the second positive lens in the second F lens group are cemented, and
wherein the second R lens group comprises one positive lens and a surface thereof on the object side has a form of decreasing positive power from an optical axis of the second R lens group toward a periphery thereof.
7. A fixed focal length image forming lens, comprising:
an aperture stop;
a first lens group arranged on an object side relative to the aperture stop; and
a second lens group having a positive power arranged on an image side relative to the aperture stop,
the first lens group comprising a first F lens group having a negative power and a first R lens group having a positive power arranged in this sequence from the object side with a widest air space within the first lens group between the first F lens group and the first R lens group, the first F lens group comprising at least two negative lenses, the first R lens group comprising at least one positive lens,
the second lens group comprising a second F lens group having a positive power and a second R lens group arranged in this sequence from the object side, the second F lens group comprising a first positive lens, a first negative lens, a second negative lens, and a second positive lens arranged in this sequence from the object side, the second R lens group comprising at least one lens,
wherein a focal length f 1 of the first lens group, a focal length f 2 of the second F lens group and a focal length f 3 of the second R lens group satisfy the following relationships (14), (16) and (17):
0.2 <f/f 2<0.5 (14)
| f 1 |/f> 8.0 (16)
0.3 >|f/f 3|>0.1 (17),
wherein f represents a focal length of the entire image forming lens, and
wherein the first positive lens and the first negative lens have a positive or negative focus synthesis length and the second negative lens and the second positive lens are cemented together as a positive cemented lens.
8. The image forming lens according to claim 7 , wherein the second negative lens and the second positive lens are cemented together to form a positive cemented lens, and wherein a positive or negative focus synthesis length f 21 of the first positive lens and the first negative lens in the second F lens and a focus synthesis length f 22 of the positive cemented lens satisfy the following relationship (15):
| f 22/ f 21|<0.5 (15).
9. The image forming lens according to claim 7 , wherein a thickness T 2 f of the second F lens group, a thickness T 1 of the first lens group, and a thickness T 2 r of the second R lens group satisfy the following relationship (18):
1 ≧T 2 f /( T 1+ T 2 r )>0.1 (18).
10. The image forming lens according to claim 7 , wherein the first positive lens and the first negative lens in the second F lens group are cemented as a cemented lens.
11. A camera device comprising:
a camera body; and
the image forming lens of claim 1 .
12. The camera device according to claim 11 , wherein the image forming lens is retractable into the camera body and the second F lens group is retractable from an optical axis of the image forming lens when the image forming lens is retracted into the camera body.
13. A handheld terminal comprising:
the camera device of claim 11 .
14. A camera device comprising:
a camera body; and
the image forming lens of claim 7 .
15. The camera device according to claim 14 , wherein the image forming lens is retractable into the camera body and the second F lens group is retractable from an optical axis of the image forming lens when the image forming lens is retracted into the camera body.
16. A handheld terminal comprising:
the camera device of claim 14 .