# US 2014/0192419 A1 · Optical system and image projection apparatus including the same

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- Number: US 2014/0192419 A1
- Document ID: US20140192419A1
- Status: Published application
- Kind: A1
- Application number: 14/148,389
- Filed: 2014-01-06
- Published: 2014-07-10
- Earliest claimed: 2013-01-08
- Assignees: Canon Kabushiki Kaisha
- Applicants: Canon Kabushiki Kaisha
- Inventors: Kazuhiro Inoko
- Web page: https://patentgrep.com/patent/US20140192419A1

## CPC

- G02B 13/04: Reversed telephoto objectives
- G02B 27/0062: {by controlling the dispersion of a lens material, e.g. adapting the relative partial dispersion}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

In an optical system including a front lens unit having negative refractive power, a stop, and a rear lens unit having positive refractive power in order from an enlargement side to a reduction side, the front lens unit has a combination lens in which a negative lens and a positive lens are adjacently arranged in order from the enlargement side to the reduction side, and a focal length of the negative lens fN, an Abbe number νN and relative partial dispersion θN of a material of the negative lens, an Abbe number νP and relative partial dispersion θP of a material of the positive lens, and a focal length of the entire optical system fW are appropriately set.

## Claims

### Claim 1

An optical system comprising, in order from an enlargement side to a reduction side:
a front lens unit having negative refractive power;
a stop; and
a rear lens unit having positive refractive power,
wherein the front lens unit includes a combination lens in which a negative lens and a positive lens are adjacently arranged in order from the enlargement side to the reduction side, and
wherein, when a focal length of the negative lens is fN, an Abbe number and relative partial dispersion of a material of the negative lens are νN and θN, respectively, an Abbe number and relative partial dispersion of a material of the positive lens are νP and θP, respectively, and a focal length of the entire optical system is fW, following conditions are satisfied:
−20<fN/fW<2
0.01<[θN−(−0.01618νN+0.6415)]−[θP−(−0.01618νP+0.6415)]<0.20.

### Claim 2 (depends on 1)

The optical system according to claim 1, wherein the optical system is a zoom lens,
wherein the front lens unit includes a plurality of lens sub-units,
wherein the rear lens unit includes a plurality of lens sub-units,
wherein distances between the lens sub-units change during zooming, and
wherein the focal length of the entire optical system fW is a focal length of the entire optical system at a wide-angle end.

### Claim 3 (depends on 1)

The optical system according to claim 1, wherein the optical system is a zoom lens,
wherein the front lens unit includes, in order from the enlargement side to the reduction side, a first lens sub-unit having negative refractive power, a second lens sub-unit having positive refractive power, a third lens sub-unit having positive refractive power, and a fourth lens sub-unit having positive refractive power,
wherein the rear lens unit includes, in order from the enlargement side to the reduction side, a fifth lens sub-unit having negative refractive power, a sixth lens sub-unit having positive refractive power, and a seventh lens sub-unit having positive refractive power,
wherein the first lens sub-unit and the seventh lens sub-unit do not move for zooming,
wherein the second lens sub-unit to the sixth lens sub-unit move during zooming, and
wherein the focal length of the entire optical system fW is a focal length of the entire optical system at a wide-angle end.

### Claim 4 (depends on 1)

The optical system according to claim 1, wherein, when a focal length of the positive lens is fP, following condition is satisfied:
−4.0<(νP−fP)/(νN−fN)<−0.2.

### Claim 5 (depends on 1)

The optical system according to claim 1, wherein following condition is satisfied:
1.0<θN/θP<1.3.

### Claim 6 (depends on 1)

The optical system according to claim 1, wherein, when a refractive index of a material of the negative lens is nN, and a refractive index of a material of the positive lens is nP, following condition is satisfied:
nP<nN.

### Claim 7 (depends on 1)

The optical system according to claim 1, wherein the negative lens and the positive lens are cemented.

### Claim 8 (depends on 1)

The optical system according to claim 1, wherein an air lens formed by the negative lens and the positive lens has positive refractive power.

### Claim 9 (depends on 1)

The optical system according to claim 1, wherein, when a refractive index of a material of the negative lens is nN, and a refractive index of a material of the positive lens is nP, following condition is satisfied:
0.1<nN−nP.

### Claim 10 (depends on 1)

The optical system according to claim 1, wherein the combination lens is a combination lens located closest to the enlargement side out of combination lenses each including a negative lens and a positive lens in order from the enlargement side to the reduction side.

### Claim 11 (depends on 1)

An image projection apparatus comprising:
a light modulation element configured to modulate incident light; and
the optical system according to claim 1 configured to project light modulated by the light modulation element.

### Claim 12 (depends on 11)

The image projection apparatus according to claim 11, wherein, when a projection angle of view of the optical system is 2ω (degree), or a projection angle of view at a wide-angle end when the optical system is a zoom lens is 2ω, following condition is satisfied:
60°<2ω.