JPH07311338A - Retro-focus type lens - Google Patents

Abstract

PURPOSE:To easily obtain a prescribed back-focus, to make the lowering of a peripheral light quantity small, and to reduce the pincushion distortion aberration even when an anamorphic lens is mounted at a wide viewing angle by setting the lens constitution so as to satisfy a specified condition. CONSTITUTION:The retro-focus type lens LFL has a first group L1 of a negative refractive power, a diaphragm SP and a second group L2 of a positive refractive power in order from a first conjugate point having a longer distance, and when the focal distance of the whole system is represented by (f), the focal distance of the ith group by fi, the air gap between the first group L1 and the second group L2 by DL12, and a distance from the final lens surface of the second group L2 at the time of the smallest image forming magnification on the side of the first conjugate point to a second conjugate point having a shorter distance is represented by bf, the conditions shown by; 1.4<bf/f, 0.65<-f1/f2<0.8, 0.05<DL12/f<0.1 are satisfied. A screen S is arranged on the side of the first conjugate point having a longer distance and a projection plane F is arranged on the side of the second conjugate point having a shorter distance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retrofocus type lens, for example, a back for a color liquid crystal projection television, which is designed such that a plurality of images having different color information are combined by a combining mirror and then enlarged and projected on a screen surface. The present invention relates to a retrofocus type lens suitable when an anamorphic lens having a long focus is attached.

[0002]

2. Description of the Related Art Conventionally, various color liquid crystal projections have been proposed, in which images displayed on a plurality of color liquid crystals (liquid crystal light valves) are optically superposed and projected on a screen surface by a projection lens. There is.

FIG. 9 is a schematic view of a main part of a color liquid crystal projection television which projects an image formed on a general color liquid crystal onto a screen surface (not shown).

In the figure, reference numeral 1 denotes a white light source which emits a collimated light beam. 2a, 2b, 2c are for red, green,
It is a liquid crystal display element for blue and displays a projected image. 3a and 3b are reflection mirrors, and 4 is a red reflection dichroic mirror for illuminating the red liquid crystal display element 2a. A green reflection dichroic mirror 5 illuminates the liquid crystal display element 2b for green. 5a is a green reflection dichroic mirror.

The blue liquid crystal display element 2c is illuminated with blue light which has passed through the red reflection dichroic mirror 4 and the green reflection dichroic mirror 5. 6 is a blue transmission dichroic mirror. 7 is a projection lens.

In the figure, white light from the white light source 1 is separated into red, green and blue color lights by the dichroic mirrors (4, 5), and the red, green and blue color lights respectively emit red,
The liquid crystal display elements (2a, 2b, 2c) for green and blue are illuminated, and the liquid crystal display elements (2a, 2c) based on the respective color lights are illuminated.
The images b, 2c) are projected on the screen surface (not shown) by the projection lens 7 to obtain a color image.

In the projection lens having such a structure, it is necessary to dispose various optical members such as a reflection mirror and a dichroic mirror between the final lens surface and the liquid crystal display element (between the back focus). Focus type lenses are often used.

[0008]

Generally, in a retrofocus lens, a lens group having a negative refractive power is arranged on the object side (the conjugate point side with a long distance), and the image plane side (the conjugate point side with a short distance).
It is composed of a lens configuration in which a lens unit having a positive refractive power is arranged. Therefore, there is a feature that a relatively long back focus can be obtained.

However, since the lens structure is asymmetric, there is a problem in that many asymmetrical aberrations such as distortion and astigmatism occur.

For example, if the back focus is made longer with respect to the screen size (effective screen), the asymmetry of the lens structure is increased, and the optical performance is significantly deteriorated.

In addition to this, since the retrofocus lens has a lens configuration in which the incident angle and the exit angle of the off-axis light beam are tight, when the off-axis angle of view increases, vignetting of the off-axis light beam increases and the illuminance around the screen increases. There is a problem that it will decrease.

When used as a lens for a color liquid crystal projection TV, which requires a particularly large image height, there is a drawback that the amount of light off the axis is small.

When the retrofocus type lens is used as a rear projection TV receiver for observing the projector from the back side of the screen, it has a wide field angle as much as possible in order to downsize the entire device and obtain a large screen. Furthermore, a very short projection distance of about half that of a general front projector is required.

When an anamorphic lens is attached to a part of the lens system to change the aspect ratio,
Since there is a pincushion type distortion aberration, a distorted distortion occurs on the projected screen, and it is required to reduce the distortion.

According to the present invention, by properly setting the lens configuration, a predetermined back focus can be easily obtained, the amount of peripheral light is less reduced, and the pincushion distortion aberration is wide even when an anamorphic lens is attached. An object of the present invention is to provide a retrofocus type lens having a high optical performance with a small number of pixels, which is particularly suitable as a projection lens for a color liquid crystal projection TV.

[0016]

The retrofocus type lens of the present invention comprises a first lens unit having a negative refractive power, a diaphragm, and a second lens unit having a positive refractive power in order from a first conjugate point having a longer distance. F), the focal length of the entire system is f, the focal length of the i-th group is fi, the air gap between the first group and the second group is DL12,
When the distance from the final lens surface of the second group to the second conjugate point having the shorter distance when the imaging magnification on the first conjugate point side is the smallest is bf, 1.4 <bf / f. (1) 0.65 <-f1 / f2 <0.8 ... (2) 0.05 <DL12 / f <0.1 ... (3) The condition is satisfied.

[0017]

1 to 3 are cross-sectional views of lenses according to Numerical Examples 1 to 3 of the present invention. 4 to 6 are numerical examples 1 of the present invention.
Object distance is infinity, 3m, 1
FIGS. 7 and 8 are graphs showing numerical examples 2 and 3 for m.
FIG. 7 is an aberration diagram when the object distance is 3 m when expressed in m units.

In the figure, LFL is a retrofocus type lens of the present invention. S is a screen, which is arranged on the side of the first conjugate point having a long distance (hereinafter, also referred to as “object side”). F is a projection surface and is arranged on the side of the second conjugate point having a short distance (hereinafter, also referred to as “image plane side”). On the image side, for example, in the case of a color liquid crystal projection as shown in FIG. 9, each element such as a liquid crystal display element which is a projected image, a light source and a filter is arranged. L1 is a first group having a negative refractive power, and L2 is a second group having a negative refractive power.
SP is a diaphragm and is arranged between the first lens unit L1 and the second lens unit L2.

The retrofocus type lens of the present invention has good optical performance by appropriately setting the refracting powers of the first and second groups, the lens group spacing and the like as in the above conditional expressions (1) to (3). When the focal length of the entire lens system is set to f while maintaining the above, the back focus (from the final lens surface which is the lens surface on the second conjugate point side when the imaging magnification on the first conjugate point side is the smallest to the second conjugate point) Distance to point) bf is bf> 1.
It is set to 4f.

Next, the technical meaning of the conditional expressions (1) to (3) will be described.

When used as a projection lens for a color liquid crystal projection TV, a long back focus is required because a dichroic mirror or the like needs to be arranged on the image plane side. Further, in order to achieve a very short projection distance, it is necessary to strengthen the refractive power of the entire projection lens system.

Conditional expression (1) is for achieving both of these conditions. That is, the refractive powers of the first group and the second group, the principal point spacing e12 of the first group and the second group, and the like are appropriately set so as to satisfy the conditional expression (1). If the conditional expression (1) is not satisfied, a predetermined back focus cannot be obtained and it becomes difficult to shorten the projection distance.

Conditional expression (2) relates to the ratio of the focal length of the first lens unit to the focal length of the second lens unit, mainly while reducing the size of the entire lens system, while ensuring a predetermined back focus and improving the optical performance. It is for keeping to. If the upper limit of conditional expression (2) is exceeded, the retrofocus type lens structure becomes weak,
It becomes difficult to keep the back focus long, and in order to intentionally lengthen it, it is necessary to increase the distance between the principal points of the first group and the second group.
It is not good because the outer diameter of the group becomes large. If the lower limit of conditional expression (2) is exceeded, the refracting power of the first lens unit will become too strong, and the image plane characteristics will become excessive. At the same time, a large amount of barrel distortion will occur on the second conjugate point side, which is not good. .

Conditional expression (3) relates to the ratio of the air distance between the first and second lens units and the focal length of the entire system, and is intended to correct various aberrations in a well-balanced manner mainly while shortening the total lens length. Is. If the upper limit of conditional expression (3) is exceeded, the total length of the lens will increase, which will increase the outer diameter of the first lens group, which is not preferable. If the lower limit of conditional expression (3) is exceeded, the distance between the principal points of the first group and the second group will also decrease. Therefore, in order to maintain the retrofocus type lens structure, the power of each lens group must be increased. As a result, good aberration correction becomes difficult, which is not good.

The retrofocus lens, which is the object of the present invention, can be achieved by satisfying the above-mentioned various conditions. Further, a predetermined back focus can be easily obtained as a projection lens for a color liquid crystal projector or the like, and distortion can be prevented. In order to satisfactorily correct off-axis aberrations such as aberrations and correct the optical performance of the entire screen in a well-balanced manner, at least one of the following conditions
It is good to satisfy one.

(1-1) The principal point distance between the first group and the second group is e
When it is 12, the condition of 0.8 <−e12 / f1 <1.2 (4) is satisfied.

Conditional expression (4) relates to the ratio of the principal point distance between the first lens group and the second lens group and the focal length of the entire system, and mainly maintains good optical performance while securing a back focus of a predetermined length. It is for the purpose.

In general, when considering the entire lens system as a thin system, bfm is the back focus when the imaging magnification on the first conjugate point side is the smallest bfm = (1-e / f1) .f. (A) Therefore, when the value of −e / f1 in the conditional expression (4) becomes large, the back focus bfm of the expression (a) becomes large, and the back focus bfs in the thick system also becomes large.

The conditional expression (4) is based on the expression (a), and the ratio between the refracting power of the first lens unit and the principal point interval deviates beyond the upper limit value or the lower limit value of the conditional expression (4). Therefore, it becomes difficult to maintain a long back focus while maintaining good optical performance of the entire screen.

(1-2) From the first conjugate point, the second group is divided into the second group a and the second group b with the largest air gap.
2a according to the projection magnification of the whole system
It is preferable to change the distance between the group and the 2b-th group.

In particular, it is preferable that the distance between the second group a and the second group b be made shorter as the distance from the first conjugate point to the second conjugate point becomes shorter.

By doing so, good optical performance is obtained over the entire screen even when the projection magnification changes.

(1-3) When the second lens unit has at least one negative lens, and the radius of curvature of the lens surface of the negative lens on the first conjugate point side and the radius of curvature of the lens surface on the second conjugate point side are Rf and Rr, respectively.

[0034]

[Equation 2] To satisfy the condition.

Conditional expression (5) is for correcting the pincushion distortion aberration generated when the anamorphic lens is attached to a part of the lens system and the screen size is changed, by the negative lens in the second group. Is. That is, the negative lens causes a barrel-shaped distortion having a predetermined magnitude. If the upper limit of conditional expression (5) is exceeded, spherical aberration will become excessive, and if the lower limit is exceeded, it will be difficult to satisfactorily correct pincushion distortion.

(1-4) First group L1 in order from the first conjugate point
Is a meniscus negative lens having a convex surface facing the first conjugate point side, both lens surfaces are convex positive lenses, a meniscus negative lens having a convex surface facing the first conjugate point side, both lens surfaces is a concave negative lens , And a positive meniscus lens having a convex surface facing the first conjugate point side. The second lens unit L2 is composed of two lens units, that is, the second lens unit L2a and the second lens unit L2b, with the widest air space as a boundary with the stop SP interposed therebetween. , A meniscus-shaped positive lens having a convex surface facing the first conjugate point side, a second lens group having a negative lens, both lens surfaces having a convex surface, and a meniscus-shaped negative lens having a convex surface facing to the first conjugate point side. It is better to have a lens and a single lens or two positive lenses.

By constructing each lens group in this way, the optical performance of the entire screen at each projection magnification is kept good.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side in the i-th lens. The refractive index of glass and the Abbe number.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical Example 1 FNO = 1: 4.7 2ω = 39.3 ° R 1 = 193.64 D 1 = 5.2 N 1 = 1.60621 ν 1 = 60.7 R 2 = 72.34 D 2 = 25.6 R 3 = 157.48 D 3 = 11.3 N 2 = 1.51884 ν 2 = 64.2 R 4 = -157.48 D 4 = 24.6 R 5 = 129.14 D 5 = 3.5 N 3 = 1.51884 ν 3 = 64.2 R 6 = 44.88 D 6 = 14.1 R 7 = -74.76 D 7 = 3.2 N 4 = 1.62633 ν 4 = 58.2 R 8 = 346.91 D 8 = 2.1 R 9 = 128.04 D 9 = 5.4 N 5 = 1.60835 ν 5 = 38.0 R10 = 506.67 D10 = 13.1 R11 = 1150.94 D11 = 7.9 N 6 = 1.70070 ν 6 = 55.5 R12 = -115.20 D12 = 5.75 R13 = 98.43 D13 = 8.4 N 7 = 1.51884 ν 7 = 64.2 R14 = 556.76 D14 = Variable R15 = -395.18 D15 = 3.9 N 8 = 1.81222 ν 8 = 41.0 R16 = 112.18 D16 = 5.8 R17 = 140.08 D17 = 12.4 N 9 = 1.49890 ν 9 = 81.6 R18 = -140.08 D18 = 0.2 R19 = 383.48 D19 = 4.3 N10 = 1.84097 ν10 = 37.2 R20 = 156.86 D20 = 4.42 R21 = 3784.31 D21 = 5.9 N11 = 1.48965 ν11 = 70.2 R22 = -299.74 D22 = 2.2 R23 = -1122.71 D23 = 11.8 N12 = 1.48965 ν12 = 70.2 R24 = -100.08

[0041]

[Table 1] Numerical Example 2 FNO = 1: 4.7 2ω = 39.5 ° R 1 = 135.42 D 1 = 5.20 N 1 = 1.56673 ν 1 = 60.7 R 2 = 67.44 D 2 = 19.47 R 3 = 156.69 D 3 = 13.57 N 2 = 1.51884 ν 2 = 64.2 R 4 = -163.19 D 4 = 24.32 R 5 = 171.72 D 5 = 3.50 N 3 = 1.51884 ν 3 = 64.2 R 6 = 44.91 D 6 = 11.21 R 7 = -68.80 D 7 = 3.20 N 4 = 1.60621 ν 4 = 60.7 R 8 = 925.27 D 8 = 2.77 R 9 = 133.60 D 9 = 7.50 N 5 = 1.62535 ν 5 = 36.3 R10 = 739.26 D10 = 9.83 R11 = (aperture) D11 = 0.00 R12 = -11137.90 D12 = 8.45 N 6 = 1.70070 ν 6 = 55.5 R13 = -104.40 D13 = 3.80 N 7 = 1.84097 ν 7 = 37.2 R14 = -121.80 D14 = 5.91 R15 = 96.60 D15 = 9.95 N 8 = 1.51884 ν 8 = 64.2 R16 = 414.88 D16 = variable R17 = -324.06 D17 = 4.85 N 9 = 1.81222 ν 9 = 41.0 R18 = 118.00 D18 = 6.62 R19 = 146.49 D19 = 12.70 N10 = 1.49890 ν10 = 81.6 R20 = -133.53 D20 = 0.20 R21 = 253.59 D21 = 4.30 N11 = 1.84097 ν11 = 37.2 R22 = 144.40 D22 = 4.21 R23 = 810.87 D23 = 5.81 N12 = 1.48965 ν12 = 70.2 R24 = -440.04 D24 = 0.20 R25 = -7117.38 D25 = 13.96 N13 = 1.48965 ν13 = 70.2 R26 = -101.94

[0042]

[Table 2] Numerical Example 3 FNO = 1: 4.7 2ω = 39.6 ° R 1 = 183.83 D 1 = 5.20 N 1 = 1.58619 ν 1 = 59.4 R 2 = 69.87 D 2 = 24.76 R 3 = 145.02 D 3 = 15.07 N 2 = 1.51884 ν 2 = 64.2 R 4 = -145.02 D 4 = 22.25 R 5 = 129.17 D 5 = 3.50 N 3 = 1.51884 ν 3 = 64.2 R 6 = 45.47 D 6 = 11.75 R 7 = -65.33 D 7 = 3.20 N 4 = 1.60621 ν 4 = 60.7 R 8 = 5333.69 D 8 = 2.27 R 9 = 165.36 D 9 = 7.50 N 5 = 1.60835 ν 5 = 38.0 R10 = 304.88 D10 = 9.01 R11 = (aperture) D11 = 2.67 R12 = 458.54 D12 = 10.51 N 6 = 1.72446 ν 6 = 50.3 R13 = -120.87 D13 = 7.37 R14 = 166.12 D14 = 9.95 N 7 = 1.51884 ν 7 = 64.2 R15 = 468.38 D15 = variable R16 = 946.93 D16 = 3.79 N 8 = 1.81222 ν 8 = 41.0 R17 = 149.49 D17 = 6.43 R18 = 138.56 D18 = 15.26 N 9 = 1.49890 ν 9 = 81.6 R19 = -138.56 D19 = 0.20 R20 = 531.95 D20 = 4.30 N10 = 1.84097 ν10 = 37.2 R21 = 120.21 D21 = 11.34 R22 = 292.42 D22 = 17.34 N11 = 1.48965 ν11 = 70.2 R23 = -115.16

[0043]

[Table 3]

[0044]

As described above, according to the present invention, by properly setting the lens configuration, a predetermined back focus can be easily obtained, the amount of peripheral light is less reduced, and the anamorphic lens with a wide angle of view is mounted. Even in such a case, it is possible to achieve a retrofocus type lens having a high optical performance with little pincushion distortion and suitable as a projection lens for a color liquid crystal projection TV.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is an aberration diagram of Numerical example 1 of the present invention when the imaging magnification is 0.

FIG. 5 is an aberration diagram of the numerical example 1 of the present invention when the imaging magnification is 0.

FIG. 6 is an aberration diagram of Numerical example 1 of the present invention when the imaging magnification is 0.

FIG. 7 is an aberration diagram of Numerical example 2 of the present invention when the imaging magnification is 0.

FIG. 8 is an aberration diagram of Numerical example 3 of the present invention when the imaging magnification is 0.

FIG. 9 is a schematic diagram of an optical system of a conventional liquid crystal projector.

[Explanation of symbols]

 LFL retrofocus type lens L1 1st group L2 2nd group L2a 2a group L2b 2b group SP Aperture S screen F Projected surface d d line g g line S.I. C Sine condition S Sagittal image plane M Meridional image plane

Claims (6)

[Claims] 1. The focal length of the entire system is defined by a first lens group having a negative refractive power, a stop, and a second lens group having a positive refractive power in order from a first conjugate point having a longer distance. f, the focal length of the i-th group is fi, and the air gap between the first and second groups is DL1
2. When the imaging magnification on the first conjugate point side is the smallest, the second
When the distance from the last lens surface of the group to the second conjugate point having the shorter distance is bf: 1.4 <bf / f 0.65 <-f1 / f2 <0.8 0.05 <DL12 / f < A retrofocus type lens characterized by satisfying the condition of 0.1. 2. The distance between the principal points of the first group and the second group is e12.
The retrofocus lens according to claim 1, wherein the condition 0.8 <-e12 / f1 <1.2 is satisfied. 3. The second lens group has, in order from the first conjugate point, two lens groups, a second lens group and a second lens group, which are spaced apart by the largest air gap, and the second lens group is arranged in accordance with the projection magnification of the entire system. Group and second
The retrofocus lens according to claim 1, wherein a distance from the group b is changed. 4. The retrofocus lens according to claim 3, wherein the distance between the second group a and the second group b is shortened as the distance from the first conjugate point to the second conjugate point is shortened. 5. The second group has at least one negative lens, and the radiuses of curvature of the lens surfaces of the negative lens on the first conjugate point side and the second conjugate point side are Rf and Rr, respectively. 1] The following conditions are satisfied: Claims 1, 2, 3
Or 4 retrofocus type lens. 6. The first group is a first group in order from the first conjugate point side.
A meniscus negative lens whose convex surface faces the conjugate point side, a positive lens whose both lens surfaces are convex surfaces, a first meniscus negative lens whose convex surface faces the first conjugate point side, a negative lens whose both lens surfaces are concave surfaces, and It has five meniscus-shaped positive lenses whose convex surface faces the one conjugate point side, and the second group is a single or cemented positive lens, and the meniscus-shaped positive lens whose convex surface faces the first conjugate point side. A lens, a negative lens, a positive lens whose both surfaces are convex, a negative meniscus lens having a convex surface facing the first conjugate point, and one or two positive lenses. 1 retro focus lens.