US 12,449,642 B2
Converter lens, interchangeable lens, and image capturing apparatus
Shinichiro Saito, Utsunomiya (JP); and Hiroki Ebe, Utsunomiya (JP)
Assigned to Canon Kabushiki Kaisha, Tokyo (JP)
Filed by CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed on Oct. 20, 2022, as Appl. No. 18/048,216.
Application 18/048,216 is a continuation of application No. 16/796,740, filed on Feb. 20, 2020, granted, now 11,586,022.
Claims priority of application No. 2019-034284 (JP), filed on Feb. 27, 2019.
Prior Publication US 2023/0110115 A1, Apr. 13, 2023
Int. Cl. G02B 13/18 (2006.01); G02B 7/02 (2021.01); G02B 15/10 (2006.01); G02B 15/12 (2006.01); G02B 15/20 (2006.01); G02B 27/00 (2006.01); G03B 17/14 (2021.01); G03B 17/58 (2021.01)
CPC G02B 13/18 (2013.01) [G02B 15/20 (2013.01); G02B 7/021 (2013.01); G02B 15/10 (2013.01); G02B 15/12 (2013.01); G02B 27/0025 (2013.01); G03B 17/14 (2013.01); G03B 17/58 (2013.01)] 23 Claims
OG exemplary drawing
 
1. 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 a total number of positive lenses included in the converter lens is four or more, and a total number of negative lens included in the converter lens is three or more, and
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.