Converter lens, interchangeable lens, and image capturing apparatus

Patent metadata

Field	Value
Publication number	US-11726305-B2
Application number	US-202217739974-A
Country	US
Kind code	B2
Filing date	May 9, 2022
Priority date	Feb 27, 2019
Publication date	Aug 15, 2023
Grant date	Aug 15, 2023

Abstract

A converter lens according to an exemplary embodiment of the present invention is a converter lens that has a negative refractive power and increases a focal length of an entire system. The converter lens includes a front group having a positive refractive power and a rear group having a negative refractive power, and the front group is a lens unit having a combined refractive power having a maximum positive refractive power in a case where the combined refractive power is obtained by combining a refractive power of each lens in order from the lens closest to an object toward an image side. At this time, a focal length of the front group, a focal length of the converter lens, and a lateral magnification of the converter lens when the converter lens is disposed on an image side of a master lens are determined as appropriate.

First claim

What is claimed is:

1. A converter lens that has a negative refractive power as a whole and is disposed on an image side of a master lens so that a focal length of an entire system becomes longer than a focal length of the master lens alone,
wherein the converter lens consists of a front unit having a positive refractive power and a rear unit having a negative refractive power,
wherein the front unit has a combined refractive power having a maximum positive refractive power in a case where the combined refractive power is obtained by a refractive power of each lens being combined in order from the lens closest to an object to an image side,
wherein the rear unit includes a first subunit and a second subunit,
wherein the second subunit consists of a positive lens closest to the image plane in the rear unit, and
wherein the following conditional expression is satisfied:
1.00< L /( sk ×β)<4.00

0.10< f 1/(|EXT_ f |×β)<0.36

0.132≤ fb /(|EXT_ f |×β)<0.35

where L is a distance on an optical axis from a lens surface closest to the object in the converter lens to a lens surface closest to the image plane in the converter lens, sk is a distance on the optical axis from a lens surface closest to the image plane in the converter lens to the image plane when the converter lens is disposed on an image side of the master lens, f1 is a focal length of the front unit, EXT_f is a focal length of the converter lens, and fb is a focal length of the second subunit.

2. The converter lens according to claim 1 , wherein the first subunit includes a second cemented lens including a positive lens and a negative lens.

3. The converter lens according to claim 2 , wherein at least one negative lens of the second cemented lens has a refraction index of 1.80 or higher with respect to a d-line.

4. The converter lens according to claim 1 , wherein the following conditional expression is satisfied:
0.10< d/sk< 0.60
where d is a distance on an optical axis from a lens surface closest to the image plane in the front unit to a lens surface closest to the object in the rear unit, and sk is a distance on the optical axis from a lens surface closest to the image plane in the converter lens to the image plane when the converter lens is disposed on an image side of the master lens.

5. The converter lens according to claim 1 , wherein the following conditional expression is satisfied:
−0.20<|EXT_ f |×Σ{(1/ N′− 1/ N )/ Rn}< 0.20

where Rn is a curvature radius of an n-th lens surface of the converter lens from the object, N′ is a refraction index of a medium on a light exit side of the n-th lens surface, N is a refraction index of a medium on a light incident side of the n-th lens surface, and EXT_f is a focal length of the converter lens.

6. The converter lens according to claim 1 , wherein the following conditional expression is satisfied:
−3.0<( R 2+ R 1)/( R 2− R 1)<−0.1

where R1 is a curvature radius of an object-side surface of the positive lens closest to an image side in the rear unit, and R2 is a curvature radius of an image-side surface of the positive lens closest to an image side in the rear unit.

7. The converter lens according to claim 1 , wherein the front unit consists of two or less lenses.

8. The converter lens according to claim 1 , wherein the number of lenses of the rear unit is greater than the number of lenses of the front unit.

9. The converter lens according to claim 1 , wherein the converter lens comprising five or more lens elements.

10. An interchangeable lens including a master lens and a converter lens that has a negative refractive power as a whole and is disposed in an optical path so that a focal length of an entire system becomes longer than a focal length of the master lens alone,
wherein the converter lens consists of a front unit having a positive refractive power and a rear unit having a negative refractive power,
wherein the front unit has a combined refractive power having a maximum positive refractive power in a case where the combined refractive power is obtained by a refractive power of each lens being combined in order from the lens closest to an object to an image side,
wherein the rear unit includes a first subunit and a second subunit,
wherein the second subunit consists of a positive lens closest to the image plane in the rear unit, and
wherein the following conditional expression is satisfied:
1.00< L /( sk ×β)<4.00

0.10< f 1/(|EXT_ f |×β)<0.36

0.132 ≤fb /(|EXT_ f |×β)<0.35

where L is a distance on an optical axis from a lens surface closest to the object in the converter lens to a lens surface closest to the image plane in the converter lens, sk is a distance on the optical axis from a lens surface closest to the image plane in the converter lens to the image plane when the converter lens is disposed on an image side of the master lens, f1 is a focal length of the front unit, EXT_f is a focal length of the converter lens, and fb is a focal length of the second subunit.

11. An image capturing apparatus including a master lens, a converter lens that collectively has a negative refractive power and is in an optical path so that a focal length of an entire system becomes longer than a focal length of the master lens alone, and an image sensor,
wherein the converter lens consists of a front unit having a positive refractive power and a rear unit having a negative refractive power,
wherein the front unit has a combined refractive power having a maximum positive refractive power in a case where the combined refractive power is obtained by a refractive power of each lens being combined in order from the lens closest to an object to an image side,
wherein the rear unit includes a first subunit and a second subunit,
wherein the second subunit consists of a positive lens closest to the image plane in the rear unit, and
wherein the following conditional expression is satisfied:
1.00< L /( sk ×β)<4.00

0.10< f 1/(|EXT_ f |×β)<0.36

0.132≤ fb /(|EXT_ f |×β)<0.35

where L is a distance on an optical axis from a lens surface closest to the object in the converter lens to a lens surface closest to the image plane in the converter lens, sk is a distance on the optical axis from a lens surface closest to the image plane in the converter lens to the image plane when the converter lens is disposed on an image side of the master lens, f1 is a focal length of the front unit, EXT_f is a focal length of the converter lens, and fb is a focal length of the second subunit.

Assignees

• Canon Kk

Inventors

• Ebe Hiroki
• Saito Shinichiro

Classifications

• G02B13/16 Primary

  for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV} · CPC title

• G02B9/10

  one + and one - component · CPC title

• G02B15/10 Primary

  by adding a part, e.g. close-up attachment · CPC title

• G02B15/1421 Primary

  the first group being positive · CPC title

• G02B13/0015

  characterised by the lens design · CPC title