PROJECTION VARIABLE FOCUSING LENS AND PROJECTION DISPLAY DEVICE

• US 20100020411A1
• Filed: 06/15/2009
• Published: 01/28/2010
• Est. Priority Date: 07/24/2008
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujinon Corporation (Fujifilm Holdings Corporation)
• Inventors: YAMAMOTO, Chikara
• Granted Patent: US 8,199,419 B2
• Time in Patent Office: Days
• US Class Current: 359/684
• CPC Class Codes: G02B 13/16 for use in conjunction with image converters or intensifiers , or for use with projectors, e.g. objectives for projection TV
• CPC Class Codes: G02B 13/22 Telecentric objectives or lens systems
• CPC Class Codes: G02B 15/144511 arranged -+-+

Abstract

Disclosed is a projection variable focusing lens and a projection display device that has a reduction side which is telecentric, a high magnifying power, a small size, a light weight, and a low manufacturing cost and is capable of correcting all aberrations occurring when power varies with good balance.

A projection variable focusing lens that moves only one lens group when power varies includes a first negative lens group G₁, a second positive lens group G₂, a third lens group G₃, and a fourth positive lens group G₄ arranged in this order from a magnification side. When a focal length varies, only the second lens group G₂ is moved along an optical axis X. During focusing, the third lens group G₃ is moved along the optical axis X. A reduction side is substantially telecentric.

Claims

1. A projection variable focusing lens comprising:

a first lens group having a negative refractive power;

a second lens group having a positive refractive power;

a third lens group; and

a fourth lens group having a positive refractive power,

wherein the first to fourth lens groups are arranged in this order from a magnification side, and

when a focal length varies, the second lens group is moved in an optical axis direction,

during focusing, the third lens group is moved in the optical axis direction, and

a reduction side is substantially telecentric.

2. The projection variable focusing lens according to claim 1,

wherein the second lens group satisfies the following conditional expression:

1.0<

f₂/f_w<

4.0

where f_w indicates the focal length of the entire system at a wide angle end, and f₂ indicates the focal length of the second lens group.

3. The projection variable focusing lens according to claim 1,

wherein the second lens group satisfies the following conditional expression:

0.15<

D₂/L<

0.55

where D₂ indicates the largest surface spacing between lenses in the second lens group and L indicates the total length of the lenses.

4. The projection variable focusing lens according to claim 1,

wherein the second lens group includes two positive lenses.

5. The projection variable focusing lens according to claim 1,

wherein the third lens group includes a first negative lens, a second positive lens having a convex surface facing the reduction side, and a third positive lens having a convex surface facing the reduction side arranged in this order from the magnification side.

6. The projection variable focusing lens according to claim 5,

wherein the fourth lens group includes one positive lens having a convex surface facing the magnification side.

7. The projection variable focusing lens according to claim 5,

wherein the third lens group satisfies the following conditional expression:

f₃/f_w<

−

3.0

where f₃ indicates the focal length of the third lens group.

8. The projection variable focusing lens according to claim 1,

wherein the first lens group has two lenses including a negative lens that has a concave surface facing the reduction side.

9. The projection variable focusing lens according to claim 1,

wherein the first lens group includes one negative lens having a concave surface facing the reduction side.

10. The projection variable focusing lens according to claim 8,

wherein the first lens group includes at least one aspheric surface.

11. The projection variable focusing lens according to claim 9,

wherein the first lens group includes at least one aspheric surface.

12. The projection variable focusing lens according to claim 1,

wherein the first lens group has two lenses including a negative lens that has a concave surface facing the reduction side,

the second lens group includes two positive lenses,

the third lens group includes a first negative lens, a second positive lens having a convex surface facing the reduction side, and a third positive lens having a convex surface facing the reduction side arranged in this order from the magnification side,

the fourth lens group includes one positive lens having a convex surface facing the magnification side, and

the entire system includes eight lenses.

13. The projection variable focusing lens according to claim 1,

wherein the first lens group includes one negative lens having a concave surface facing the reduction side,

the second lens group includes two positive lenses,

the third lens group includes a first negative lens, a second positive lens having a convex surface facing the reduction side, and a third positive lens having a convex surface facing the reduction side arranged in this order from the magnification side,

the fourth lens group includes one positive lens having a convex surface facing the magnification side, and

the entire system includes seven lenses.

14. A projection display device comprising:

at least one light source;

at least one light valve;

at least one illumination optical unit that guides light emitted from the light source to the light valve; and

the projection variable focusing lens according to claim 1,

wherein the light valve modulates the light emitted from the light source, and

the modulated light is projected onto a screen by the projection variable focusing lens.