Converter lens, interchangeable lens, and image-capturing apparatus
A converter lens (RCL) has a negative refractive power, which is disposed on an image side of a master lens (ML) to make a focal length of an entire system longer than that of the master lens alone. The converter lens comprises a most image-side lens element (LT) disposed closest to an image side in the converter lens, wherein the most image-side lens element has a lens surface having a convex shape toward an image side, a lens disposed closest to an image side in the converter lens has a positive refractive power, and mN<mP and 0.0≤LR 2 /AR 2 <1.0 are satisfied.
1. A converter lens having a negative refractive power, which is disposed on an image side of a master lens to make a focal length of an entire system longer than a focal length of the master lens alone, the converter lens comprising:
a most image-side lens element disposed closest to an image side in the converter lens,
wherein the most image-side lens element has a lens surface having a convex shape toward an image side,
wherein a lens disposed closest to an image side in the converter lens has a positive refractive power, and
wherein the following conditional expressions are satisfied:
mN<mP
0.0≤ LR 2/ AR 2<1.0
where mP is the number of positive lens components of the converter lens, mN is the number of negative lens components of the converter lens, LR 2 is a radius of curvature of an image-side lens surface of the most image-side lens element, and AR 2 is a radius of curvature of an object-side lens surface of the most image-side lens element.
2. The converter lens according to claim 1 ,
wherein the converter lens includes at least two positive lenses, and
wherein the following conditional expression is satisfied:
1.58< nAP< 1.80
where nAP is an average refractive index at a d line of materials of all positive lenses included in the converter lens.
3. The converter lens according to claim 1 ,
wherein the converter lens includes at least one negative lens, and
wherein the following conditional expression is satisfied:
1.80< nAN< 2.20
where nAN is an average refractive index at a d line of materials of all negative lenses included in the converter lens.
4. The converter lens according to claim 1 , further comprising:
a lens element adjacent to an object side of the most image-side lens element,
wherein the following conditional expression is satisfied:
0.0≤ LR 2/ AR 1<0.9
where AR 1 is a radius of curvature of an image-side lens surface of the lens element adjacent to an object side of the most image-side lens element.
5. The converter lens according to claim 1 ,
wherein the most image-side lens element includes a single lens having a positive refractive power, which is disposed closest to an image side, and
wherein the following conditional expression is satisfied:
0.05<| fLP/f|< 0.60
where fLP is a focal length of the single lens and f is a focal length of the converter lens.
6. The converter lens according to claim 1 ,
wherein the most image-side lens element includes a single lens having a positive refractive power, which is disposed closest to an image side, and
wherein the following conditional expression is satisfied:
1.45< nLP< 1.75
where nLP is an average refractive index at a d line of materials of the single lens.
7. The converter lens according to claim 1 , further comprising:
a lens element adjacent to an object side of the most image-side lens element,
wherein the following conditional expression is satisfied:
0.0≤ LR 2/ BR 2<1.0
where BR 2 is a radius of curvature of an object-side lens surface of the lens element adjacent to an object side of the most image-side lens element.
8. The converter lens according to claim 1 , further comprising:
a lens element adjacent to an object side of the most image-side lens element,
wherein the following conditional expression is satisfied:
0.4< AR 2/ AR 1<2.0
where AR 1 is a radius of curvature of an image-side lens surface of the lens element adjacent to an object side of the most image-side lens element.
9. The converter lens according to claim 1 ,
wherein the following conditional expression is satisfied:
−7.0< SFL<− 1.0
where SFL is a shape factor of the most image-side lens element.
10. The converter lens according to claim 1 , further comprising:
a most object-side lens element disposed closest to an object side in the converter lens,
wherein the following conditional expression is satisfied:
0.1<| fl/f|< 0.9
where fl is a focal length of the most object-side lens element and f is a focal length of the converter lens.
11. The converter lens according to claim 1 , further comprising:
a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented in order from an object side to an image side.
12. The converter lens according to claim 1 , further comprising:
a most object-side lens element disposed closest to an object side in the converter lens; and
a lens element adjacent to an image side of the most object-side lens element,
wherein an object-side lens surface of the lens element adjacent to an image side of the most object-side lens element is concave toward an object side.
13. The converter lens according to claim 1 , further comprising:
a most object-side lens element disposed closest to an object side in the converter lens; and
a lens element adjacent to an image side of the most object-side lens element,
wherein an image-side lens surface of the lens element adjacent to an image side of the most object-side lens element is concave toward an image side.
14. The converter lens according to claim 1 ,
wherein the most image-side lens element has a positive refractive power.
15. The converter lens according to claim 1 ,
wherein all lenses that compose the converter lens are spherical lenses.
16. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens and a positive lens are cemented, a third lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, and a fourth lens element which is a positive single lens.
17. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, a third lens element which is a cemented lens in which a positive lens and a negative lens are cemented, and a fourth lens element which is a positive single lens.
18. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, a third lens element which is a positive single lens, and a fourth lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, and a fifth lens element which is a positive single lens.
19. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, a third lens element which is a positive single lens, a fourth lens element which is a cemented lens in which a negative lens and a positive lens are cemented, and a fifth lens element which is a cemented lens in which a negative lens and a positive lens are cemented.
20. An interchangeable lens comprising:
a master lens; and
a converter lens having a negative refractive power, which is disposed on an image side of the master lens to make a focal length of an entire system longer than a focal length of the master lens alone,
wherein the converter lens includes a most image-side lens element disposed closest to an image side in the converter lens,
wherein the most image-side lens element has a lens surface having a convex shape toward an image side,
wherein a lens disposed closest to an image side in the converter lens has a positive refractive power, and
wherein the following conditional expressions are satisfied:
mN<mP
0.0≤ LR 2/ AR 2<1.0
where mP is the number of positive lens components of the converter lens, mN is the number of negative lens components of the converter lens, LR 2 is a radius of curvature of an image-side lens surface of the most image-side lens element, and AR 2 is a radius of curvature of an object-side lens surface of the most image-side lens element.
21. An image-capturing apparatus comprising:
a master lens;
a converter lens having a negative refractive power, which is disposed on an image side of the master lens to make a focal length of an entire system longer than a focal length of the master lens alone; and
an image sensor configured to receive an image formed by the converter lens,
wherein the converter lens includes a most image-side lens element disposed closest to an image side in the converter lens,
wherein the most image-side lens element has a lens surface having a convex shape toward an image side,
wherein a lens disposed closest to an image side in the converter lens has a positive refractive power, and
wherein the following conditional expressions are satisfied:
mN<mP
0.0≤ LR 2/ AR 2<1.0
where mP is the number of positive lens components of the converter lens, mN is the number of negative lens components of the converter lens, LR 2 is a radius of curvature of an image-side lens surface of the most image-side lens element, and AR 2 is a radius of curvature of an object-side lens surface of the most image-side lens element.