JP3049676B2 - Projection optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system, and more particularly to a projection optical system having a high optical performance for miniaturizing an entire lens system when an original projected image displayed on a color liquid crystal is enlarged and projected on a screen surface. It relates to an optical system.

[0002]

2. Description of the Related Art Conventionally, various projection optical systems have been proposed in which a projection image original such as a film image or a liquid crystal light valve is enlarged and projected on a screen surface.

Various types of projection optical systems are used, but a projection optical system using a color liquid crystal as an original projected image reflects light in the space (back focus) from the final lens surface to the liquid crystal display element. What has long back focus in order to arrange optical members, such as a mirror and a dichroic mirror, is desired. For this reason, a retrofocus type, which is preceded by a lens group having a negative refractive power, is often used as a projection optical system for a color liquid crystal.

FIG. 6 is a schematic view of a main part of a projection optical system proposed in Japanese Patent Application Laid-Open No. 61-13885. In FIG. 1, reference numeral 20 denotes a light source, 19 denotes a lens, and 21 denotes an elliptical reflecting mirror, which reflects a light beam from the light source 20 to the lens 19 side. Reference numeral 12 denotes a broadband polarization beam splitter that reflects, for example, only the S-polarized light component.

Reference numeral 13 denotes a color separation prism having a blue reflection dichroic surface, and reference numeral 14 denotes a color separation prism having a red reflection dichroic surface. Reference numeral 15 denotes an optical block for correcting an optical path length. 16, 17, and 18 are liquid crystal devices, respectively.

In FIG. 1, a light beam from a light source 20 is
, Only the S-polarized light component is reflected by the polarization beam splitter 12. The color separation prisms 13 and 14 separate the color into three color lights of blue light, red light and green light, and illuminate the liquid crystal devices 16, 17 and 18, respectively. From the liquid crystal device, reflected light whose polarization plane is rotated based on the original projected image is obtained. Thus, the original projected images of the liquid crystal devices (16, 17, 18) are synthesized via the color separation prism and the polarization beam splitter 12, and are enlarged and projected on the screen surface by the projection lens 11.

[0007]

In the projection optical system shown in FIG. 7, a projection lens 11 and a liquid crystal device (16, 17, 1) are used.
8), a polarization beam splitter 12 and color separation prisms 13 and 14 are arranged. Therefore, the projection lens 1
1 requires a long back focus, for example, three times or more the width of the liquid crystal device (16, 17, 18).

In general, to have a long back focus, the entire lens system is provided with a lens unit having a negative refractive power on the screen side and a lens unit having a positive refractive power on the original projected image side.
It must be a so-called retro type.

However, in the case of the retro type, since the lens system becomes asymmetric, various aberrations increase, and it becomes difficult to obtain good optical performance. In addition, there is a problem that the number of lenses increases and the entire lens system becomes complicated and large.

According to the present invention, by appropriately setting the lens configuration of the projection lens and the configuration of the illuminating means for illuminating the original projected image such as a liquid crystal panel, it is possible to reduce the size of the entire apparatus without requiring a long back focus. It is an object of the present invention to provide a projection optical system in which the projection is prevented.

[0011]

SUMMARY OF THE INVENTION The features of the projection optical system of the present invention are described below.
The feature is that the original projected image is projected on the screen surface.
Projection optical system, the projection optical system is the screen
The first lens unit having a negative refractive power and the
Two lens groups, one plano-convex lens convex to the screen side
Has three lens groups, a third lens group having a positive refractive power
Projection lens, and illumination light between the second group and the third group
Introduction means, and the illumination light introduction means is arranged outside the optical path.
Reflected from the light source unit toward the third lens group,
The projection image original image is illuminated with the light beam passing through the third lens group,
Using the reflected light from the projected image original, the projected image original is
It is to project on the lean surface. And preferably the second
The focal length of the i-th group is Fi, the focal length of the whole system is F, and
Let the principal point interval of the (i + 1) th group be e _i, And -2 <F₁/F<-0.5(1) 1 <F_Two/F<2.5(2) 1 <F_Three/ F <3 (3) 0.5 <e₁/ F <3 (4) 1.5 <e_Two/ F <5 (5).

[0012]

1 and 2 are schematic views of a main part of an optical system according to Embodiments 1 and 2 of the present invention, respectively. In FIG. 1, reference numeral 11 denotes a projection lens, which has a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and a first lens unit L1 having a positive refractive power that is convex toward the screen. It has three lens groups L3. In the figure, the first lens group is moved along the optical axis to focus (focus adjustment).
It is carried out. SP is an aperture.

Reference numeral 9 denotes a light source unit which emits a white light beam and is arranged outside the optical path of the projection lens 11. Reference numeral 4 denotes an illumination light introducing means, which comprises a half mirror surface, and
It is arranged near the stop SP between the lens group and the third lens group. The illumination light introducing means 4 reflects, for example, a light beam from the light source unit 9 in the direction of the third lens group, and illuminates a projection image original image (6, 7, 8) to be described later. S is a screen surface.

Reference numeral 5 denotes a color separating means, which has a dichroic surface therein and separates and emits an incident light beam into, for example, three color lights of blue light, green light and red light. Reference numerals 6, 7 and 8 denote reflection type liquid crystal panels (liquid crystal devices) as original projection images.

In this embodiment, a part of the light beam radiated from the light source unit 9 is reflected in the direction of the third lens group by the illumination light introducing means 4 and passes through the third lens group. The original projected image (6, 7, 8) is illuminated by being decomposed into two color lights.

By arranging the illumination light introducing means 4 for illuminating the original projected image (6, 7, 8) between the second lens group and the third lens group, the projection lens 11 is required. Back focus is shortened.

Thus, in the present embodiment, the original projected image (6,
7, 8) are superimposed via the color separation means 5 and enlarged and projected on the screen surface S by the projection lens 11. At this time, focus (focus adjustment) is performed by moving all the lens units of the first lens unit on the optical axis.

The stop SP is disposed near the illumination light introducing means 4 between the second lens group and the third lens group, and the projection lens 1
1, the amount of distortion is reduced. In this embodiment, the stop SP may be disposed at any position between the second lens group and the third lens group. Illumination light introducing means 4
May be used in combination as an aperture.

In this embodiment, a half mirror is used as the illumination light introducing means. However, a dot mirror in which minute reflecting portions and transmitting portions are provided regularly or randomly may be used.

FIGS. 2 and 3 are lens sectional views of numerical examples 1 and 2 of the projection lens according to the present invention. In the figure, reference numeral 11 denotes a projection lens. The projection lens 11 has three lens groups: a first lens group L1 having a negative refractive power, a second lens group L2 having a positive refractive power, and a third lens group L3 having a positive refractive power. 4 is an illumination light introducing means, 5 is a color separation means, SP is a stop, and 22 is a color filter.

FIGS. 4 and 5 are aberration diagrams when the projection magnification of the numerical examples 1 and 2 of the projection lens of the present invention is 40 times.

In this embodiment, the refracting power of each lens group, the principal point interval, and the like are appropriately set as described above, thereby obtaining a predetermined back focus while reducing the size of the entire lens system with a small number of lenses. The optical performance of the projected image is maintained satisfactorily, and the aberration fluctuation when focusing is performed by the first lens group is satisfactorily corrected.

Next, the technical meaning of the above conditional expression will be described.

Conditional expression (1) relates to the ratio of the focal length of the first lens unit having negative refractive power to the focal length of the entire system. This is for reducing the fluctuation of aberration.

If the negative refractive power of the first lens unit becomes too weak below the lower limit value of the conditional expression (1), the amount of movement of the first lens unit during focusing becomes too large, and the overall length of the lens becomes longer.
On the other hand, if the negative refractive power exceeds the upper limit and the negative refractive power becomes too strong, the amount of movement at the time of focusing is reduced, but the field curvature of the entire screen increases in the positive direction.

The conditional expressions (2) and (3) relate to the ratios of the focal lengths of the second and third lens groups to the focal length of the entire system, respectively. The principal rays mainly entering the original projection image are substantially parallel. This is for projecting onto a screen surface while maintaining good telecentricity and maintaining a good balance of color reproduction and various aberrations of the original projection image.

If conditional expressions (2) and (3) are not satisfied, it is difficult to maintain telecentricity while maintaining various aberrations in good condition, and project while maintaining a good balance of the optical performance of the entire original projected image. It becomes difficult.

Conditional expression (4) relates to the ratio of the distance between the principal points of the first and second groups to the focal length of the entire system, and is mainly conditional expression (1)
Based on (3), the entire lens system is designed to be a retro type in which a predetermined back focus can be easily obtained.

If the distance between the principal points is too short beyond the lower limit value of the conditional expression (4), the degree of retrograde is weakened, the back focus is shortened and the focal length of the entire system is lengthened.
On the other hand, if the distance between the principal points exceeds the upper limit value and the interval between the principal points is too long, the retro degree becomes too strong, the back focus becomes longer than a predetermined value, and the overall length of the lens increases.

Condition (5) relates to the ratio of the distance between the principal points of the second and third lens groups with respect to the focal length of the entire system.
This is for appropriately obtaining a space for disposing the illumination light introducing means having a predetermined size between the second group and the third group.

If the distance between the principal points is too short below the lower limit value of conditional expression (5), it is difficult to arrange the illumination light introducing means. The whole becomes large, and it becomes difficult to correct various aberrations in a well-balanced manner.

In this embodiment, in order to minimize the ghost of the third lens group generated by the light incident from the illumination system, the third lens group is constituted by a plano-convex lens convex to the screen side. It is desirable that the plano-convex lens be adhered or adhered to the dichroic prism with an adhesive or a liquid close to the refractive index of the plano-convex lens.

Next, numerical examples of the present invention will be described. In the numerical examples, ri is the radius of curvature of the i-th lens surface in order from the screen side, di is the i-th lens thickness and air spacing from the screen side, and ni and νi are the i-th lens in order from the object side. Are the refractive index and Abbe number of the glass.

R21 to R24 in Numerical Embodiment 1 and r19 to r22 in Numerical Embodiment 2 are glass blocks such as color separation means and color filters.

[0035]

[Table 1]

[0036]

[Outside 1]

[0037]

[Outside 2]

[0038]

According to the present invention, as described above, by appropriately setting the lens configuration of the projection lens and the configuration of the illuminating means for illuminating the original projected image such as the liquid crystal panel, it is possible to obtain a predetermined back focus and It is possible to achieve a projection optical system capable of easily enlarging and projecting an original projection image on a screen surface in a focused state while reducing the number of entire lenses and preventing the entire apparatus from being enlarged.

In particular, by forming the third lens group with one plano-convex lens convex to the screen side, the ghost generated by the incident light of the illumination system could be extremely reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of an optical system according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a lens according to Numerical Example 1 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 4 is a diagram showing various aberrations at a projection magnification of 40 times in Numerical Example 1 of the present invention.

FIG. 5 is a diagram illustrating various aberrations at a projection magnification of 40 times in Numerical Example 2 of the present invention.

FIG. 6 is a sectional view of a conventional general projection system.

[Explanation of symbols]

 I1 Projection lens L1 First lens group L2 Second lens group L3 Third lens group 4 Illumination light introducing means 5 Color separation means 6, 7, 8 Projected original image 9 Light source unit SP stop d d-line g g-line M Meridional image plane S sagittal image plane

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04 G02F 1/13 G03B 21 / 00 G03B 21/14

Claims (3)

(57) [Claims] 1. A projection optical system for projecting an original projected image onto a screen surface, wherein the projection optical system includes a first lens unit having a negative refractive power, a second lens group having a positive refractive power, and A third lens group consisting of one plano-convex lens convex to the screen side; and an illumination light introducing means between the second lens group and the third lens group, wherein the illumination light introducing means is located outside the optical path. The light beam from the light source unit disposed is reflected to the third lens group side, the original projected image is illuminated with the light beam passing through the third lens group, and the projected image is reflected using the reflected light from the original projected image. A projection optical system for projecting an original image on the screen surface. 2. When the focal length of the i-th lens unit is Fi, the focal length of the whole system is F, and the distance between principal points between the i-th lens unit and the (i + 1) -th lens unit is ei, −2 <F ₁ / F <−0. .5 1 <F ₂ /F<2.5 1 <F ₃ / F <3 0.5 <e ₁ / F <3 1.5 <e ₂ / F <5 The projection optical system according to claim 1. 3. The projection optical system according to claim 2, wherein focusing is performed by moving said first lens group.