Converter lens, interchangeable lens, and image capturing apparatus
AssigneeCanon Kabushiki Kaisha
InventorsShinichiro Saito, Hiroki Ebe
Life of this patent
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Abstract
A converter lens has negative refractive power, and is disposed on an image side of a master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone. The converter lens includes a first lens element closest to an object and a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element. A focal length of the converter lens, a focal length of an air lens formed by the first lens element and the second lens element, the shape of an image-side lens surface of the first lens element, and the shape of an object-side lens surface of the second lens element are determined as appropriate.
Claims20
A converter lens having negative refractive power and disposed on an image side of a master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone, the converter lens comprising:
- a first lens element closest to an object in the converter lens;
- and
- a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element,
- wherein the following inequalities are satisfied:
- 1.45<|fa/f|<8.55;
- −80.0<(ra2+ra1)/(ra2−ra1)<−2.00;
- and
- 30.0<νAN<39.0,
- where f is a focal length of the converter lens, na1 is a d-line refractive index of a material of an image-side lens of the first lens element, na2 is a d-line refractive index of a material of an object-side lens of the second lens element, ra1 is a curvature radius of the image-side lens surface of the first lens element, ra2 is a curvature radius of the object-side lens surface of the second lens element, fa is a focal length of the space between the first lens element and the second lens element and is defined as fa=1/[{(1/ra1)×(1−na1)/na2}−{(1/ra2)×(1−na2)/na2} ], and νAN is an average Abbe number of a material of every negative lens included in the converter lens.
An interchangeable lens comprising a master lens and a converter lens having negative refractive power and configured to be inserted to or removed from an optical path of the master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone, the converter lens comprising:
- a first lens element closest to an object in the converter lens;
- and
- a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element,
- wherein the following inequalities are satisfied:
- 1.45<|fa/f|<8.55;
- −80.0<(ra2+ra1)/(ra2-ra1)<−2.00;
- and
- 30.0<νAN<39.0,
- where f is a focal length of the converter lens, na1 is a d-line refractive index of a material of an image-side lens of the first lens element, na2 is a d-line refractive index of a material of an object-side lens of the second lens element, ra1 is a curvature radius of the image-side lens surface of the first lens element, ra2 is a curvature radius of the object-side lens surface of the second lens element, fa is a focal length of the space between the first lens element and the second lens element and is defined as fa=1/[{(1/ra1)×(1−na1)/na2}−{(1/ra2)×(1−na2)/na2}], and νAN is an average Abbe number of a material of every negative lens included in the converter lens.
An image capturing apparatus comprising:
- a master lens;
- a converter lens having negative refractive power and disposed on an optical path of the master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone;
- and
- an image sensor,
- the converter lens comprising:
- a first lens element closest to an object in the converter lens;
- and
- a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element,
- wherein the following inequalities are satisfied:
- 1.45<|fa/f|<8.55;
- −80.0<(ra2+ra1)/(ra2−ra1)<−2.00;
- and
- 30.0<νAN<39.0,
- where f is a focal length of the converter lens, na1 is a d-line refractive index of a material of an image-side lens of the first lens element, na2 is a d-line refractive index of a material of an object-side lens of the second lens element, ra1 is a curvature radius of the image-side lens surface of the first lens element, ra2 is a curvature radius of the object-side lens surface of the second lens element, fa is a focal length of the space between the first lens element and the second lens element and is defined as fa=1/[{(1/ra1)×(1−na1)/na2}−{(1/ra2)×(1-na2)/na2}], and νAN is an average Abbe number of a material of every negative lens included in the converter lens.
Dependencies are inferred from the claim text.