JP2005084455A - Telecentric zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized zoom lens for a liquid crystal projector. <P>SOLUTION: The zoom lens is constituted of negative, positive, positive, positive, negative and positive lens groups in this order from a magnifying side, and a distance between a 2nd lens group and a 3rd lens group is shortened at zooming. A 5th lens group is shifted to a screen side (magnifying side), a 4th lens group is shifted to the screen side (magnifying side), the 2nd lens group is shifted to a panel side (reduction side), a 1st lens group and a 6th lens group are fixed. The zoom lens is constituted so that a 4th lens group has the largest zooming assignment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a zoom lens used in a projection apparatus that magnifies and projects an image onto a screen at a fixed finite distance, and in particular, uses a plurality of liquid crystals or the like for each color light as a display body and performs color synthesis to project a single image. The present invention relates to a simple small telecentric zoom lens that projects high-definition images via a lens.

  A negative lead type zoom lens preceded by a lens unit having a negative refractive power has features such as a relatively wide angle of view and the ability to maintain performance at close-up shooting distances. There are disadvantages such as an increase in the amount of movement for doubling and difficulty in achieving high zooming.

  For example, Japanese Patent Publication No. 49-23912, Japanese Patent Publication No. 53-34539, Japanese Patent Publication No. 57-163213 have disclosed zoom lenses in which these disadvantages are improved and the entire lens system is reduced in size and increased in magnification. JP-A-58-4113, JP-A-63-241511, and JP-A-2-201310.

  In each of these gazettes, a lens group having negative, positive, negative, and positive refractive powers as a whole is composed of four lens groups in order from the zoom lens object side. It is carried out.

  Japanese Patent Application Laid-Open No. 54-17019 has many groups. In the present invention, so-called optical compensation is performed, and in particular, the second lens group and the fourth lens group are moved in the same manner. With this OPCON configuration, restrictions are severe and the size is easily increased for the zoom ratio. Further, this configuration has a short exit pupil and is not suitable for a projection lens.

  In recent years, many proposals have been made for a multi-group configuration for a zoom lens used in a projection apparatus that performs enlarged projection on a screen. For example, Japanese Laid-Open Patent Publication No. 11-95098 proposes a zoom lens having a negative, positive, and negative four-group configuration. However, many of these proposals have a dark specification as a lens and are not sufficient for producing a bright projected image.

  Japanese Patent Application Laid-Open No. 10-186235 proposes a zoom lens having a five-group configuration of negative positive positive negative positive. Many of these proposals have a dark specification as a lens and are not sufficient to produce a bright projected image.

  In addition, the present applicant has proposed a projection zoom lens having a five-group configuration of negative positive, negative, positive and positive in Japanese Patent Application Laid-Open No. 11-190821, and has proposed a brighter and more compact lens.

  When the display image is enlarged and projected on the screen as in the present invention, particularly when the liquid crystal display is divided into a plurality of colors and the respective color lights are combined and projected by a single projection lens, the following conditions are satisfied. It is necessary to do.

  1) A so-called telecentric optical system in which the exit pupil is at a distance, taking into consideration the light distribution characteristics of the liquid crystal and the projection directivity of the illumination system. Further, when color composition is performed using a member having a dichroic film such as a cross dichroic prism, it is preferably telecentric to reduce color unevenness.

  2) A long back focus or a space between the lenses is required in order to secure a space for the color synthesis element for synthesizing a plurality of display bodies.

  3) Normally, in order to project the display image on the screen upward, the display body is used with its center position shifted with respect to the optical axis of the projection lens. As a result, the effective area used in the vicinity of the front lens is the optical axis. Since it is not symmetrical, it is biased upward and the diameter of the front lens becomes large, so an improvement means is necessary.

  In contrast to the above requirements, in the conventional example, it is difficult to say that the exit pupil position is finite and the back focus is sufficiently long. In addition, since the number of constituent groups is small, the movable group for zooming is limited, and the amount of movement of each group becomes large and the sensitivity becomes high in order to obtain the desired magnification. In many cases, the projected image was significantly deteriorated just by the presence of.

  Also, in recent proposals, there are many lenses that are not lenses with sufficient brightness to project brightly on a screen.

  The present invention is an improvement of Japanese Patent Application Laid-Open No. 11-190821 by the present applicant. The number of constituent groups is large, the sensitivity of each group is reduced, the projector is bright and downsized, and the distortion is small. An object of the present invention is to provide a projection lens.

  In order to achieve the above object, the present invention is characterized by the following configuration.

In an approximately telecentric zoom lens that magnifies and projects an image on the display screen onto the screen, in order from the screen side (magnification side),
A first lens unit having a negative refractive power;
A second lens unit having a positive refractive power;
A third lens unit having a positive refractive power;
A fourth lens unit having a positive refractive power;
A fifth lens unit having negative refractive power;
A sixth lens unit having a positive refractive power;
When the focal length at the wide-angle end is changed to the focal length at the telephoto end, the distance between the second lens group and the third lens group is configured to be narrow. As a result of the above configuration, the third lens group is reduced during zooming. However, as will be described later, the fourth lens group is most multiplied, and is suitable for obtaining a desired zoom ratio.

  Further, when the focal length at the wide-angle end is changed to the focal length at the telephoto end, the fifth lens group is configured to be closer to the screen side (enlargement side) than the wide-angle end at the telephoto end, and the fifth lens group is increased. It is preferable to contribute to the doubling.

  In particular, when a transition is made from the focal length at the wide-angle end to the focal length at the telephoto end, the fourth lens group moves to the screen side (enlargement side), and the second lens group moves to the panel side (reduction side). This is preferable for effective zooming.

  In particular, when transitioning from the focal length at the wide-angle end to the focal length at the telephoto end, the fourth lens group should contribute most to the zooming. For this reason, when transitioning from the focal length at the wide-angle end to the focal length at the telephoto end The fourth lens group is preferably located on the screen side (enlargement side) from the wide angle end at the telephoto end, and the second lens group is located on the panel side (reduction side) from the wide angle end at the telephoto end. .

  The third lens group is also preferably moved to the screen side (enlargement side).

Especially when transitioning from the focal length at the wide-angle end to the focal length at the telephoto end,
The distance between the second lens group and the third lens group is narrowed, and the distance between the fourth lens group and the fifth lens group is widened. The third lens group is closer to the screen side (enlarged) than the wide-angle end. It is preferable that it exists in front).

  At this time, it is preferable that the fourth lens group has the largest variable magnification share.

  Further, the third lens group is demagnified when changing from the wide-angle end to the telephoto end.

  The largest moving amount is that of the third lens group or the fourth lens group.

Here, if the amount of movement from the wide-angle end to the telephoto end of the i-th lens group is Mi and the movement to the panel side (reduction side) is positive (+), 0.6 <M2 / M4 <1.8 (1 )
Is preferably satisfied.

  If the upper limit is exceeded, the entire system becomes larger, and if the lower limit is exceeded, it becomes difficult to obtain a desired zoom ratio.

  Moreover, it is preferable that the following conditions are satisfied.

−0.4 <M2 / M4 <−0.04 (2)
When this lower limit is exceeded, the size is increased, and when the upper limit is exceeded, it is difficult to secure a desired zoom ratio, and this is not appropriate.

  In particular, it is desirable for the sixth lens group to be fixed during zooming in order to suppress pupil fluctuations during zooming.

  Further, if the first lens group is fixed during zooming, it is effective for downsizing the entire system, and functions can be shared by using only for distance adjustment, which is effective in terms of performance and mechanism.

  The sixth lens group is closest to the display body and provides a relatively strong positive refractive power, thereby realizing a telecentric system.

  The final lens may act like a field lens, and a color synthesis prism may be introduced on the screen side (enlargement side). At that time, a polarizing plate or a color filter may be attached to the final lens. In that case, the final lens is closest to the display surface (panel), especially the panel side (reduction side) surface is flat or close to a flat surface, and a positive lens with a strong convex surface facing the screen side (enlargement side) is arranged. Is preferred.

  By moving the second lens group, the third lens group, the fourth lens group, and the fifth lens group to change the magnification, the amount of movement of each group is reduced, and the positional deviation, tilting, etc. of each group is reduced. A low zoom lens with a high degree of magnification can be achieved by reducing the sensitivity of the front lens, reducing the overall length and shortening the distance from the entrance pupil position to the front lens, which is determined by the off-axis oblique luminous flux. The diameter can be reduced.

  The first lens group has a negative refractive power and ensures a long back focus because of the space of the color synthesizing element. In particular, in order to increase the back focus, it is preferable to dispose a negative meniscus lens having a convex surface on the screen side (enlargement side) in the first lens group. Further, by appropriately arranging the refractive power of each group and fixing the first lens group during zooming, the position of the off-axis oblique light beam can be reduced, thereby simplifying the configuration and providing a lens system with a constant overall length. Can be achieved. Further, in order to reduce distortion at the wide-angle end, a convex lens is disposed closest to the object side of the first lens group, and distortion correction is performed at a position through which the off-axis light beam passes most.

Especially at the focal length at the telephoto end, compared to the focal length at the wide-angle end,
The distance between the first lens group and the second lens group increases,
The distance between the second lens group and the third lens group decreases,
The distance between the fourth lens group and the fifth lens group increases,
It is preferable that the distance between the fifth lens group and the sixth lens group is increased in order to appropriately disperse the variable magnification share of each group and to obtain a desired variable magnification ratio.

  At this time, it is preferable that the fourth lens group is multiplied upon zooming.

  For the fourth lens group, which is the main variable power group, it is preferable to satisfy the following expression.

Assuming that the magnification βit / βiw of the i-th lens group is Zi and the change in focal length ft / fw of the entire system is Z, 1.015 <Z4 / Z <1.4 (3)
This expression (3) makes the ratio of zooming of the fourth lens group, which is a zooming group, appropriate. Although the fourth lens group is magnified during zooming, it is appropriate in view of the variable magnification sharing of the entire system to be within this range in consideration of the balance of zooming with other lens groups.

  The focal length of the entire system at the wide-angle end is fw, the focal length of the entire system at the telephoto end is ft, the focal length of the first lens group is f1, the focal length of the second lens group is f2, and the focal length of the third lens group is When f3, the focal length of the fourth lens group is f4, the focal length of the fifth lens group is f5, and the focal length of the sixth lens group is f6, it is preferable that the following expression is satisfied.

0.15 <| f1 / f2 | <0.5 (4)
2.0 <f2 / √ (fw × ft) <8.0 (5)
1.3 <f4 / √ (fw × ft) <2.0 (6)
The above equation (4) appropriately defines the relationship between the first lens group and the second lens group that are involved in the front lens diameter and distortion.

  If the value deviates from the lower limit of the expression (4), the front lens diameter determined by the first lens group increases, and distortion at the wide-angle end increases, which is not appropriate. On the other hand, if the value deviates from the upper limit, the desired angle of view (especially the wide angle side) becomes difficult and the entire system becomes large and is not suitable.

  Expression (5) makes the power of the second lens group appropriate, and if the lower limit is exceeded, the image plane becomes overcorrected and is not appropriate. On the other hand, if the upper limit is exceeded, it is necessary to increase the amount of movement of the second lens unit in order to obtain a desired zoom ratio, which makes the entire system larger and unsuitable.

  Expression (6) makes the power of the fourth lens unit of the variable power group appropriate, and if the lower limit is exceeded, the image plane is overcorrected and is not appropriate. On the other hand, if the upper limit is exceeded, it is necessary to increase the amount of movement of the second lens unit in order to obtain a desired zoom ratio, which makes the entire system larger and unsuitable.

  In particular, the group contributing to zooming preferably satisfies the following conditions.

1.4 <f2 / f4 <4.5 (7)
This expression (7) makes the refractive power arrangement of the lens group contributing to zooming appropriate.

  If the value deviates from the upper limit value, the refractive power of the fourth lens group of the main variable power group becomes strong and the field curvature tends to increase. On the other hand, if the value deviates from the lower limit, the refractive power of the fourth lens unit of the main variable power group becomes weak, making it difficult to obtain a desired variable power ratio.

  In particular, in order to appropriately correct distortion, it is preferable that the following expression is satisfied.

0.8 <| f1 | / fw <1.5 (8)
If the upper limit of this expression is deviated, an appropriate back focus cannot be secured, and if the lower limit is exceeded, distortion at the wide-angle end increases with a negative value, which is not appropriate.

  The distance between the most screen side (enlargement side) surface of the sixth lens unit and the display body (panel) at the wide angle end (the distance including the cross dichroic color synthesizing system on the most display body side) is D. , It is preferable that the following formula is satisfied.

0.6 <f6 / D <1.0 (9)
If the upper limit of this equation is exceeded, the color composition system becomes difficult to enter, and if the upper limit is exceeded, the pupil becomes shorter and is not appropriate.

  The reason for setting the exit side (reduction side) of the lens to be substantially telecentric is to eliminate the influence of the light distribution characteristics of the liquid crystal or the angle dependency of the color synthesis dichroic mirror when combining multiple color lights as described above. is there. Specifically, in order to eliminate the angle dependency, it is preferable if the following conditions are satisfied.

| Tk | / fw> 1.5 (10)
More preferably, it is desirable to be within the following range.

| Tk | / fw> 5.5 (10a)
Here, tk is the distance from the display panel at the wide-angle end to the exit pupil (from the reduction side conjugate position). (Here, the exit pupil is the pupil on the reduction side.)
In particular, it is preferable to satisfy the following conditions in order to optimize the distance from the lens to the panel while optimizing the telecentric system.

1.1 <f6 / fw <1.4 (11)
If the lower limit is exceeded, optimum telecentricity cannot be satisfied, and if the upper limit is exceeded, the size is increased and is not suitable.

  Furthermore, it is preferable to satisfy the following expression in order to reduce the size by making the movement amount of each group appropriate while making the power arrangement of each group appropriate.

0.7 <| f1 | / √ (fw × ft) <1.5 (12)
2.0 <f3 / √ (fw × ft) <7.0 (13)
1.5 <| f5 | / √ (fw × ft) <6.0 (14)
0.8 <f6 / √ (fw × ft) <1.5 (15)
In particular, in the case where a fixed lens (field lens / condenser lens) is provided between the display body (panel) and the color synthesizing prism, in order to reduce the size of the prism, an off-axis main lens protruding from the panel (reduction side conjugate surface) is used. It is preferable that the light beam (center light beam) is incident on the fixed lens substantially perpendicularly (telecentric), and then enters the color synthesis prism and proceeds to the screen side (enlargement side) at an angle toward the optical axis ( (See the sectional view of Example 2). With this configuration, the size of the volumetric color synthesis prism can be reduced, which can contribute to the reduction of the entire system. At this time, all of the three colors of RGB to be color-synthesized have the above-mentioned fixed lenses, which is disadvantageous in terms of cost and the like, but downsizing the prism is also beneficial in terms of cost and the like. In addition, it is preferable to dispose the fixed lens having the same focal length and different chromatic dispersion (Abbe number) in consideration of the chromatic aberration of magnification of each RGB, so that the color shift in the synthesis is further reduced. At that time, a polarizing plate or a color filter may be attached to the final fixed lens as described above. In that case, the final fixed lens is closest to the display surface (panel), and in particular the panel side (reduction side) surface is flat or close to a flat surface, and a positive lens with a strong convex surface facing the screen side (enlargement side) is arranged. It is preferable to do this.

  In particular, it is preferable for miniaturization to satisfy the following conditions.

When the image circle of the lens is L and the effective diameter of the lens immediately before the screen side (enlargement side) of the color synthesis prism is E, E / L <1.05 (16)
If the value deviates from the upper limit at this time, the size of the color synthesizing prism increases, which is not appropriate.

  With the configuration described above, the number of constituent groups is large, the sensitivity of each group is reduced, the brightness is reduced, the size is reduced, and high-definition image projection used for an enlarged projection projection apparatus with less distortion is performed. A simple small telecentric zoom lens could be achieved.

  Examples 1 to 6 of the present invention will be described below with reference to the drawings and tables.

  Table 1 shows the calculation results obtained by calculating the values of the conditional expressions (1) to (16) regarding Examples 1 to 6.

  Next, lens data of Examples 1 to 6 are shown in Tables 2 to 7, diagrams showing the lens configurations of Examples 1 to 6 are shown in FIGS. 1 to 6, and aberration diagrams in the lens configurations of Examples 1 to 6 are shown in FIGS. Shown in

In the first embodiment, there is no field (condenser) lens on the panel side (reduction side) of the color synthesis prism. In this example, the distance between the third lens group and the fourth lens group decreases when the lens is displaced from the wide-angle end to the telephoto end. | M3 | <| M4 |
The second to fifth embodiments are examples in which a field (condenser) lens is provided on the panel side (reduction side) of the color synthesis prism. The second embodiment and the third embodiment are examples in which the opening diameter (F number) is different from the fourth embodiment and the fifth embodiment. In these examples, the distance between the third lens group and the fourth lens group increases when the lens is displaced from the wide-angle end to the telephoto end. | M3 | >> | M4 |
In the fifth example, M3 / M4 is the largest, and the power of the third lens group is the weakest.

  In the sixth embodiment, there is no field (condenser) lens on the panel side (reduction side) of the color synthesis prism. In this example, the distance between the third lens group and the fourth lens group decreases when the lens is displaced from the wide-angle end to the telephoto end. | M3 | <| M4 |. This is an example that deviates from the most telecentric configuration.

  Focusing is preferably performed with the first lens group, but is performed simultaneously with the first lens group and the second lens group, or with the sixth group, or with a plurality of groups, particularly at a finite distance and with a moving amount for each group. The distance may be adjusted, or the entire display panel may be moved or the display panel may be moved.

FIG. 5 is a diagram illustrating a lens configuration of Example 1. FIG. 5 is a diagram illustrating a lens configuration of Example 2. FIG. 5 is a diagram illustrating a lens configuration of Example 3. FIG. 5 is a diagram illustrating a lens configuration of Example 4. FIG. 10 is a diagram illustrating a lens configuration of Example 5. FIG. 6 shows a lens configuration of Example 6. Aberration diagram of the lens configuration of Example 1 Aberration diagram in the lens configuration of Example 2 Aberration diagram of the lens configuration of Example 3 Aberration diagrams in the lens configuration of Example 4 Aberration diagram of the lens configuration of Example 5 Aberration diagram of the lens configuration of Example 6

Claims (5)

In an approximately telecentric zoom lens that magnifies and projects an image on the display screen onto the screen, in order from the screen side (magnification side),
A first lens unit having a negative refractive power;
A second lens unit having a positive refractive power;
A third lens unit having a positive refractive power;
A fourth lens unit having a positive refractive power;
A fifth lens unit having negative refractive power;
A sixth lens unit having a positive refractive power;
A zoom lens, wherein the distance between the second lens group and the third lens group becomes narrow when the focal length at the wide-angle end is changed to the focal length at the telephoto end. When transitioning from the focal length at the wide-angle end to the focal length at the telephoto end,
2. The zoom lens according to claim 1, wherein the fifth lens group is on the screen side (enlargement side) from the wide angle end at the telephoto end. When transitioning from the focal length at the wide-angle end to the focal length at the telephoto end,
The fourth lens group is on the screen side (enlargement side) from the wide-angle end at the telephoto end, and the second lens group is on the panel side (reduction side) from the wide-angle end at the telephoto end. The zoom lens according to item 1.   The zoom lens according to claim 1, wherein the sixth lens group is fixed during zooming. The zoom lens according to claim 1, wherein the first lens group is fixed during zooming.

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