Converter lens, interchangeable lens, and image capturing apparatus

Patent metadata

Field	Value
Publication number	US-11474332-B2
Application number	US-202016796764-A
Country	US
Kind code	B2
Filing date	Feb 20, 2020
Priority date	Feb 27, 2019
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

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 the image side, and
wherein the following conditional expressions are satisfied:
0.11< f 1/(|EXT- f |×β)≤0.257

1.00< L /( sk ×β)<4.00

where f1 is a focal length of the front unit, EXT_f is a focal length of the converter lens, β is a lateral magnification of the converter lens when the converter lens is disposed on an image side of the master lens, 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, 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.

2. The converter lens according to claim 1 ,
wherein the rear unit includes a first subunit and a second subunit, and
wherein the second subunit consists of a first cemented lens closest to an image plane in the rear unit or a positive lens closest to the image plane in the rear unit, the first cemented lens including a positive lens and a negative lens and having a positive refractive power as a whole.

3. The converter lens according to claim 2 , wherein the following conditional expression is satisfied:
0.03< fa /(|EXT_ f |×β)<0.15

where fa is a focal length of the first subunit.

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

5. The converter lens according to claim 4 , 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.

6. The converter lens according to claim 2 , wherein the following conditional expression is satisfied:
0.10< fb /(|EXT_ f |×β)<0.35

where fb is a focal length of the second subunit.

7. 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.

8. 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, and N is a refraction index of a medium on a light incident side of the n-th lens surface.

9. 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 a lens closest to the image plane in the converter lens, and R2 is a curvature radius of an image-side surface of the lens closest to the image plane in the converter lens.

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

11. 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.

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

13. 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, and
wherein the following conditional expressions are satisfied:
0.11< f 1/(|EXT- f |×β)≤0.257

1.00< L /( sk ×β)<4.00

where f1 is a focal length of the front unit, EXT_f is a focal length of the converter lens, β is a lateral magnification of the converter lens when the converter lens is disposed on an image side of the master lens, 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, 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.

14. 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, and
wherein the following conditional expressions are satisfied:
0.11< f 1/(|EXT- f |×β)≤0.257

1.00< L /( sk ×β)<4.00

where f1 is a focal length of the front unit, EXT_f is a focal length of the converter lens, β is a lateral magnification of the converter lens when the converter lens is disposed on an image side of the master lens, 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, 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.

Assignees

• Canon Kk

Inventors

• Ebe Hiroki
• Saito Shinichiro

Classifications

• H04N23/00

  Cameras or camera modules comprising electronic image sensors; Control thereof · CPC title

• H04N23/55

  Optical parts specially adapted for electronic image sensors; Mounting thereof · CPC title

• G02B15/10 Primary

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

• G02B13/0015

  characterised by the lens design · CPC title

• G02B9/10

  one + and one - component · CPC title