Lens system, optical device with lens system, and method of manufacturing lens system
A lens system comprises, on a side closest to an object, a first lens component having a positive refractive power and a second lens component having a positive refractive power in order from the object; and on a side closest to an image, a cemented lens constructed by cementing together a positive lens and a negative lens in order from the object; wherein the lens system satisfies the following conditional expressions: ( n 1+ n 2)/2>1.49 (ν1+ν2)/2>60 where n 1 and ν 1 denote a refractive index and an Abbe number of the first lens component at d-line, respectively, and n 2 and ν 2 denote a refractive index and an Abbe number of the second lens component at d-line, respectively.
1. A lens system comprising:
on a side closest to an object, a first lens component having a positive refractive power and a second lens component having a positive refractive power in order from the object; and
on a side closest to an image, a cemented lens constructed by cementing together a positive lens and a negative lens in order from the object;
wherein the lens system satisfies the following conditional expressions:
( n 1+ n 2)/2>1.49
(ν1+ν2)/2>60
where n 1 and ν 1 denote a refractive index and an Abbe number of the first lens component at d-line, respectively, and n 2 and ν 2 denote a refractive index and an Abbe number of the second lens component at d-line, respectively, and further comprising:
a front-side negative lens component having a negative refractive power, an aperture stop, a rear-side negative lens component having a negative refractive power, and a rear-side positive lens component having a positive refractive power in order from the object between the second lens component and the cemented lens.
2. A lens system according to claim 1 , wherein each of the first and second lens components has a meniscus form with a convex surface facing the object.
3. A lens system according to claim 1 , further comprising a third lens component having a meniscus form with a convex surface facing the object between the second lens component and the front-side negative lens component.
4. A lens system according to claim 1 , wherein the front-side negative lens component is a fourth lens component having a meniscus form with a convex surface facing the object, and wherein the rear-side negative lens component is a fifth lens component having a double concave form.
5. A lens system according to claim 1 , further comprising a seventh lens component having a positive refractive power between a sixth lens component as the rear-side positive lens component and the cemented lens.
6. A lens system according to claim 1 , wherein the rear-side negative lens component and the rear-side positive lens component are cemented together so as to form a cemented lens.
7. A lens system according to claim 1 , wherein the lens system satisfies the following conditional expressions:
n8>n9
ν8>ν9
where n 8 and ν 8 denote a refractive index and an Abbe number of the positive lens in the cemented lens arranged closest to the image at d-line, respectively, and n 9 and ν 9 denote a refractive index and an Abbe number of the negative lens in the cemented lens arranged closest to the image at d-line, respectively.
8. A lens system according to claim 1 , wherein the lens system satisfies the following conditional expression:
0.3< r 8/ f< 0.5
where r 8 denotes a radius of curvature of an image-side surface of the front-side negative lens component, and f denotes a focal length of the lens system as a whole.
9. A lens system according to claim 1 , wherein the lens system satisfies the following conditional expression:
1< f 89/ f< 2
where f 89 denotes a focal length of the cemented lens arranged closest to the image, and f denotes a focal length of the lens system as a whole.
10. A lens system according to claim 1 , wherein the positive lens in the cemented lens arranged closest to the image has a double convex form.
11. An optical device including the lens system according to claim 1 .
12. A method of manufacturing a lens system, the method comprising the steps of:
arranging, on a side closest to an object, a first lens component having a positive refractive power and a second lens component having a positive refractive power in order from the object; and
arranging, on a side closest to an image, a cemented lens constructed by cementing together a positive lens and a negative lens in order from the object;
wherein the lens system satisfies the following conditional expressions:
( n 1+ n 2)/2>1.49
(ν1+ν2)/2>60
where n 1 and ν 1 denote a refractive index and an Abbe number of the first lens component at d-line, respectively, and n 2 and ν 2 denote a refractive index and an Abbe number of the second lens component at d-line, respectively, and
wherein the lens system further comprises a front-side negative lens component having a negative refractive power, an aperture stop, a rear-side negative lens component having a negative refractive power, and a rear-side positive lens component having a positive refractive power in order from the object between the second lens component and the cemented lens.
13. A lens system according to claim 1 , wherein, upon focusing, the cemented lens arranged closest to the image is moved at a speed different from that of any other lens arranged along an optical axis of the lens system and included in the lens system.
14. The method of manufacturing a lens system according to claim 12 , wherein, upon focusing, the cemented lens arranged closest to the image is moved at a speed different from that of any other lens arranged along an optical axis of the lens system and included in the lens system.