Converter lens, interchangeable lens, and image capturing apparatus

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
• 0.15<|f1/f|≤0.520,
• 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 f1 is a focal length of the first lens element.

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
• 0.15<|f1/f|≤0.520,
• 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 f1 is a focal length of the first lens element.

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;
• 0.01<|f1/fa|≤0.195;
• and
• 0.02<rl/f<0.32
• 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}], f1 is a focal length of the first lens element ,and rl is a curvature radius of an image-side lens surface of a lens closest to an image in the converter lens.

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 second lens element includes a cemented lens including a negative lens, a positive lens, and a negative lens in this order from an object side to an image side.
• wherein the following inequalities are satisfied:
• 1.45<|fa/f|<8.55;
• −80.0<(ra2+ra1)/(ra2−ra1)<−2.00;
• 0.01<|f1/fa|≤0.195;
• and
• 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 f1 is a focal length of the first lens element.