JP4006073B2 - Zoom lens - Google Patents

Description

【００５３】

【００５４】

【００５５】

【００５６】

【００５７】
また、次表は実施例１〜５におけるレンズ系の各数値、条件式の数値である。
【００５８】

【００５９】

【００６０】
更に、図６〜図１５は各実施例１〜５の収差図である。
【００６１】
【発明の効果】
以上説明したように本発明に係るズームレンズは、簡易な構成で明るく小型で高変倍で歪曲も小さく倍率色収差の発生も少なく、高精細な画像投影を行い簡易で小型化を達成することができる。
【図面の簡単な説明】
【図１】第１実施例のレンズ断面図である。
【図２】実施例２のレンズ断面図である。
【図３】実施例３のレンズ断面図である。
【図４】実施例４のレンズ断面図である。
【図５】実施例５のレンズ断面図である。
【図６】第１実施例の広角状態の収差図である。
【図７】第１実施例の望遠状態の収差図である。
【図８】実施例２の広角状態の収差図である。
【図９】実施例２の望遠状態の収差図である。
【図１０】実施例３の広角状態の収差図である。
【図１１】実施例３の望遠状態の収差図である。
【図１２】実施例４の広角状態の収差図である。
【図１３】実施例４の望遠状態の収差図である。
【図１４】実施例５の広角状態の収差図である。
【図１５】実施例５の望遠状態の収差図である。
【符号の説明】
Ｌ１ 第１レンズ群
Ｌ２ 第２レンズ群
Ｌ３ 第３レンズ群
Ｌ４ 第４レンズ群
Ｌ５ 第５レンズ群
ΔＭ メリディオナル焦線
ΔＳ サジタル焦線[0001]
BACKGROUND OF THE INVENTION
The present invention is a zoom lens used in a projection device that enlarges and projects an image onto a screen at a fixed finite distance. In particular, the display body uses a plurality of liquid crystals or the like for each color light, and color-synthesizes one projection. The present invention relates to a simple, small, and substantially telecentric zoom lens that projects a high-definition image through a lens.
[0002]
[Prior art]
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 zooming and difficulty in high zooming.
[0003]
Zoom lenses that improve these disadvantages and reduce the overall size of the lens system and increase the zoom ratio are disclosed in, for example, Japanese Patent Publication Nos. 49-23912, 53-34539, and 57-163213. JP-A-58-4113, JP-A-63-241511, JP-A-2-201310 and the like.
[0004]
In each of these publications, the zoom lens is composed of four lens groups as a whole of negative, positive, negative, and positive refractive power groups in order from the object side, and a predetermined lens group is appropriately moved among them. We are zooming.
[0005]
[Problems to be solved by the invention]
However, when the display image is enlarged and projected on the screen as in the present invention, the liquid crystal display body is divided into a plurality of color lights, and each color light is synthesized and projected by one projection lens. It is necessary to satisfy the following conditions.
[0006]
(1) A so-called telecentric optical system in which the exit pupil is far away in order to eliminate the influence of the light distribution characteristics of the liquid crystal or the angle dependency of the color synthesis dichroic mirror when synthesizing a plurality of color lights.
[0007]
(2) A long back focus is required to secure a space for the color synthesizing element interposed between the display body and the projection lens.
[0008]
(3) Normally, in order to project the display image upward on the screen, 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 to be used is near the front lens. Since it is not symmetrical with respect to the optical axis, it is biased upward and the diameter of the front lens becomes large, so an improvement means is necessary.
[0009]
In response to such requirements, it is difficult to say that the exit pupil position is finite and the back focus is sufficiently long in the prior art.
[0010]
An object of the present invention is to solve the above-described problems and provide a zoom lens having a simple configuration, a small size, and high performance.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a zoom lens according to the present invention is a zoom lens for enlarging and projecting an image of a display surface onto a screen, in order from the screen side, a first lens group having a negative refractive power, and a positive refractive power. the second lens group, third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power, is composed of a fifth lens unit having positive refractive power, in the transition from wide-angle end to the telephoto end, the The second lens group and the fourth lens group move to the screen side, the focal length of the zoom lens at the wide angle end is fw, the screen side is negative, and the display surface side is positive. The position of the exit pupil with respect to the display surface when the absolute value of the distance from the surface to the exit pupil of the zoom lens is minimum is tk, the focal length of the fifth lens group is f5, and 5 lens group on the most the equivalent air length from the lens surface on the display surface side bf, when the focal length of the first lens group and the f1,
tk / fw <-4.0
0.380981 ≦ bf / f5 <0.5
1.2 <| f1 | / bf <2.2
It is characterized by satisfying.
A projection apparatus includes the zoom lens according to any one of claims and a display body having a display surface, and projects an image displayed on the display surface on a screen in an enlarged manner.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail based on the embodiments shown in the drawings.
FIG. 1 is a lens cross-sectional view of the first embodiment. In a telecentric zoom lens that magnifies and projects onto a screen, a first lens unit L1 having a negative refractive power and a second lens unit L2 having a positive refractive power are sequentially arranged from the screen side. The third lens unit L3 has a negative refractive power, the fourth lens unit L4 has a positive refractive power, and the fifth lens unit L5 has a positive refractive power. At the telephoto end focal length, the distance between the first lens unit L1 and the second lens unit L2 decreases, the interval between the second lens unit L2 and the third lens unit L3 increases, and the focal length at the telephoto end increases. Each lens group is appropriately moved so that the distance between the third lens group L3 and the fourth lens group L4 is decreased, and the distance between the fourth lens group L4 and the fifth lens group L5 is increased. For this purpose, the first lens unit L1 and the fifth lens unit L5 are fixed, and the remaining second lens unit L2 and fourth lens unit L4 are moved to the screen side to change the magnification. At this time, the third lens unit L3 is moved so as to correct the fluctuation of the image plane accompanying the movement of the second lens unit L2 and the fourth lens unit L4, but it is particularly preferable that the third lens unit L3 is moved by a convex locus on the screen side.
[0013]
The fifth lens unit L5 is closest to the display body and provides a relatively strong positive refractive power, thereby realizing a telecentric system. Further, it is desirable that the fifth lens unit L5 is configured by a single positive lens having a strong convex surface facing the screen side, thereby achieving both correction of off-axis field curvature and simplification of the configuration.
[0014]
By moving the second lens group L2, the third lens group L3, and the fourth lens group L4 to change the magnification, it is possible to achieve a zoom lens with a high zoom ratio while reducing the amount of movement of each group. The distance from the entrance pupil position to the front lens is shortened, and the front lens diameter determined by the off-axis oblique light beam can be reduced.
[0015]
The first lens unit L1 has a negative refractive power and ensures a long back focus because of the space of the color synthesis 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 in the first lens unit L1. Further, by appropriately arranging the refractive power of each group and fixing the first lens unit L1 during zooming, the variation in the position of the off-axis oblique light beam is reduced, and the lens having a uniform overall length with a simplified configuration. The system can be achieved. Further, in order to reduce distortion at the wide-angle end, a convex lens is arranged on the most object side of the first lens unit L1, and distortion correction is performed at a position where the most off-axis light beam passes.
[0016]
Focusing to a finite distance is preferably performed by the first lens unit L1, but the third lens unit, the fifth lens unit, or a plurality of lens units may be used for distance adjustment by different amounts of movement. You can do this by moving the screen.
[0017]
The first example shown in FIG. 1 is zooming from the wide-angle end to the telephoto end. The first lens unit L1 and the fifth lens unit L5 are fixed during zooming, and the second lens unit L2 and the fourth lens unit L4 are fixed. While moving to the screen side, the third lens unit L3 moves along a convex locus toward the screen side with an inflection point near the telephoto end, and has the largest aperture.
[0018]
In the second embodiment shown in FIG. 2, zooming from the wide-angle end to the telephoto end is performed similarly to the first embodiment. The first lens unit L1 and the fifth lens unit L5 are fixed during zooming, and the second lens unit L2 The fourth lens unit L4 moves to the screen side, and the third lens unit L3 moves along a locus convex toward the screen side with an inflection point in the vicinity of the telephoto end, and the zoom ratio is large.
[0019]
Example 3 shown in FIG. 3 is an example of a lens configuration different from Example 2. During zooming from the wide-angle end to the telephoto end, the first lens unit L1 and the fifth lens unit L5 are fixed during zooming, the second lens unit L2 and the fourth lens unit L4 move to the screen side, and the third lens The group L3 moves along a locus convex toward the screen with an inflection point in the vicinity of the telephoto end.
[0020]
In Example 4 shown in FIG. 4, zooming from the wide-angle end to the telephoto end causes the first lens unit L1 to move along a convex locus toward the screen side, and the telephoto end is positioned closer to the display panel than the wide-angle end. The fifth lens unit L5 is fixed during zooming, the second lens unit L2 and the fourth lens unit L4 move to the screen side with the same movement amount, and the third lens unit L3 has an inflection point in the vicinity of the telephoto end. Move along a convex trajectory.
[0021]
Example 5 shown in FIG. 5 is zooming from the wide-angle end to the telephoto end, the first lens unit L1 and the fifth lens unit L5 are fixed during zooming, and the second lens unit L2 and the fourth lens unit L4 are screens. And the third lens unit L3 is also fixed during zooming.
[0022]
More preferably, in these embodiments, the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and ft, the focal length of the first lens unit L1 is f1, the focal length of the second lens unit L2 is f2, When the focal length of the third lens unit L3 is f3, the focal length of the fourth lens unit L4 is f4, and the focal length of the fifth lens unit L5 is f5, it is preferable that the following conditional expression is satisfied.
[0023]
1.1 <| f1 | / f2 <2.3 (1)
0.6 <f2 / (fw · ft) ^1/2 <1.2 (2)
[0024]
These conditional expressions (1) and (2) appropriately define the relationship between the second lens unit L2 and the first lens unit L1, which are the main variable magnification groups. If the lower limit of the conditional expression (1) is exceeded, The front lens diameter determined by the first lens unit L1 is increased, and distortion at the wide angle end is increased, which 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 L2 in order to obtain a desired zoom ratio.
[0025]
Conditional expression (2) makes the refractive power of the main variable magnification group appropriate. If the lower limit is exceeded, the image surface 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 L2 in order to obtain a desired zoom ratio, which makes the entire system large and unsuitable.
[0026]
In particular, in order to properly correct the distortion, it is preferable to satisfy the following expression.
[0027]
1 <| f1 | / fw <2 (3)
[0028]
If the upper limit of conditional expression (3) is exceeded, distortion at the wide-angle end cannot be performed properly, and if the lower limit is exceeded, distortion at the telephoto end cannot be performed properly.
[0029]
Note that the substantially telecentric system or the telecentric system referred to in this specification 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 synthesizing a plurality of color lights as described above. It shows that the exit pupil is far away (ideally at infinity). Specifically, in order to eliminate the angular dependence, the exit pupil with respect to the display surface when the absolute value of the distance from the display panel to the (reduction side) exit pupil (enlargement side) is minimized during zooming. Is set to tk (where the screen side (enlarged side) is minus and the display surface (reduced side) is plus as in the following numerical examples 1 to 5),
tk / fw <-4.0 (4)
[0030]
Furthermore, it is desirable that it falls within the following range.
[0031]
| Tk | / fw> 9.0 (4) '
[0032]
For the second lens unit L2, which is the main zoom unit, the change β2t / β2w of the magnification β2 of the second lens unit L2 is Z2, and the focal length change ft / fw of the entire system is Z. When the movement amounts in zooming of the second lens unit L2 and the fourth lens unit L4 are M2 and M4, respectively, it is preferable to satisfy the following expressions.
[0033]
0.8 <Z2 / Z <1.1 (5)
0.9 <M2 / M4 <1.6 (6)
0.4 <M2 / (ft−fw) <1.0 (7)
[0034]
Conditional expression (5) appropriately defines the ratio of zooming in the second lens unit L2 and the fourth lens unit L4 that are the zooming unit. The third lens unit L3 is preferably in this range because it is reduced upon zooming. Conditional expressions (6) and (7) make the length of the entire lens and the amount of movement of each zooming group appropriate. In particular, in the second lens unit L2 and the fourth lens unit L4, the refractive power of the fourth lens unit L4 tends to be weak, so this range is preferable for appropriate variable magnification sharing. In particular, it is more preferable that the moving amount of the second lens unit L2 exceeds the moving amount of the fourth lens unit L4.
[0035]
As described above, in the second lens unit L2 and the fourth lens unit L4, the refractive power of the fourth lens unit L4 tends to be weak, and it is particularly preferable to satisfy the following expression.
[0036]
0.4 <f2 / f4 <0.8 (8)
[0037]
Conditional expression (8) and conditional expression (6) are necessary for appropriately setting the Petzval sum while appropriately adjusting the refractive power arrangement and zooming of the main zooming group.
[0038]
In order to appropriately set the exit pupil and distortion of the entire system, the following equation is satisfied, where bf is the distance from the fifth lens unit L5 to the display body and the air equivalent length excluding the dichroic prism and the like. Is preferred.
[0039]
0.3 <bf / f5 <0.5 (9)
1.2 <| f1 | / bf <2.2 (10)
[0040]
Conditional expression (9) is necessary to make the entire system appropriately telecentric. When the upper limit is exceeded, the size increases, and when the lower limit is exceeded, distortion occurs. Conditional expression (10) is also a condition for lengthening the exit pupil while appropriately taking distortion to make a telecentric system.
[0041]
In particular, in order to optimize the distance from the lens to the panel while optimizing the telecentric system, it is preferable to satisfy the following conditional expression.
[0042]
2 <f5 / fw <3.5 (11)
[0043]
If the lower limit value of the conditional expression (11) is exceeded, optimum telecentricity cannot be satisfied, and if the upper limit value is exceeded, the size is increased and is not appropriate.
[0044]
Furthermore, in order to reduce the size by appropriately moving the respective groups while appropriately arranging the refractive power arrangement of each group, it is preferable to satisfy the following expression.
[0045]
1.0 <| f1 | / (fw · ft) ^1/2 <1.6 (12)
0.6 <| f3 | / (fw · ft) ^1/2 <1.2 (13)
1.1 <f4 / (fw · ft) ^1/2 <1.8 (14)
1.5 <f5 / (fw · ft) ^1/2 <3.0 (15)
[0046]
In particular, it is preferable that the third lens unit L3 includes a lens having an Abbe number ν3 in the following range in order to reduce the chromatic aberration of magnification during zooming and suppress fluctuations.
[0047]
ν3> 55 (16)
[0048]
In particular, preferably
ν3> 60… (16) '
It is good to have a lens in the range.
[0049]
Further, by configuring the average Abbe number ν1n of the negative lenses constituting the first lens unit L1 as in the following expression, it is possible to reduce variations due to chromatic aberration and zooming.
[0050]
ν1n> 60 (17)
[0051]
Next, Numerical Examples 1 to 5 of Examples 1 to 5 are shown. In these numerical examples 1 to 5, ri is the radius of curvature of the i-th lens surface from the screen side, di is the i-th lens thickness or air spacing, ni and ν i are the refractive indices of the i-th lens and the Abbe number. It is.
[0052]

[0053]

[0054]

[0055]

[0056]

[0057]
The following table shows the numerical values of the lens systems and conditional expressions in Examples 1 to 5.
[0058]

[0059]

[0060]
Further, FIGS. 6 to 15 are aberration diagrams of Examples 1 to 5. FIG.
[0061]
【The invention's effect】
As described above, the zoom lens according to the present invention has a simple configuration, is bright and small, has a high zoom ratio, is distorted with little distortion, and produces a high-definition image, thereby achieving simple and miniaturization. it can.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view of a first embodiment.
2 is a lens cross-sectional view of Example 2. FIG.
3 is a lens cross-sectional view of Example 3. FIG.
4 is a lens cross-sectional view of Example 4. FIG.
5 is a lens cross-sectional view of Example 5. FIG.
FIG. 6 is an aberration diagram in the wide-angle state according to the first example.
FIG. 7 is an aberration diagram for the telephoto state of the first example.
FIG. 8 is an aberration diagram of Example 2 in a wide angle state.
FIG. 9 is an aberration diagram for Example 2 in a telephoto state.
10 is an aberration diagram of Example 3 in a wide angle state. FIG.
11 is an aberration diagram for Example 3 in a telephoto state. FIG.
12 is an aberration diagram for Example 4 in the wide-angle state. FIG.
13 is an aberration diagram for Example 4 in a telephoto state. FIG.
14 is an aberration diagram of Example 5 in a wide angle state. FIG.
15 is an aberration diagram for Example 5 in a telephoto state. FIG.
[Explanation of symbols]
L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L5 5th lens group ΔM Meridional focal line ΔS Sagittal focal line

Claims (15)

In a zoom lens for enlarging and projecting an image of a display surface onto a screen, in order from the screen side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens unit having a positive refractive power, is composed of a fifth lens unit having a positive refractive power moves, when transitioning from the wide-angle end to the telephoto end, the second lens group, the fourth lens group to the screen side When the focal length of the zoom lens at the wide-angle end is fw, the screen side is negative, and the display surface side is positive, the absolute value of the distance from the display surface to the exit pupil of the zoom lens is The position of the exit pupil with respect to the display surface at the minimum is tk, the focal length of the fifth lens group is f5, and the distance from the display surface to the lens surface closest to the display surface of the fifth lens group. Air change Long bf, when the focal length of the first lens group and the f1,
tk / fw <-4.0
0.380981 ≦ bf / f5 <0.5
1.2 <| f1 | / bf <2.2
A zoom lens characterized by satisfying   The distance between the second lens group and the third lens group increases and the distance between the third lens and the fourth lens group decreases at the focal length at the telephoto end compared to the focal length at the wide-angle end. The zoom lens according to 1.   At the focal length at the telephoto end with respect to the focal length at the wide-angle end, the distance between the first lens group and the second lens group decreases, and the distance between the second lens group and the third lens group increases. 3. The zoom lens according to claim 2, wherein a distance between the third lens and the fourth lens group decreases, and a distance between the fourth lens and the fifth lens group increases.   2. The zoom lens according to claim 1, wherein the second lens group includes at least two positive lenses and one negative lens, and the third lens group includes at least one negative lens. The focal length of the entire system of the telephoto end ft, when the focal length of the second lens group and f2, the zoom lens according to claim 1 which satisfies the following condition.
1.1 <| f1 | / f2 <2.3
0.6 <f2 / (fw · ft) ^1/2   When a transition is made from the focal length at the wide-angle end to the focal length at the telephoto end, the second lens group and the fourth lens group move to the screen side, and the third lens group moves from the wide-angle end to the The zoom lens according to claim 1, wherein a position of a telephoto end is on the screen side.   When a transition is made from the focal length at the wide-angle end to the focal length at the telephoto end, the second lens group and the fourth lens group move to the screen side, and the third lens group is convex to the screen side. The zoom lens according to claim 6, which moves along a locus.   4. The zoom lens according to claim 3, wherein the first lens group is fixed during zooming when a transition is made from the focal length at the wide-angle end to the focal length at the telephoto end. The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
1 <| f1 | / fw <2 The focal length of the entire system at the telephoto end is ft, the ratio of the magnification between the telephoto end and the wide-angle end of the second lens group is Z2, the ratio of the focal length of the wide-angle end to the telephoto end of the entire system is Z, and the second lens 2. The zoom lens according to claim 1, wherein the zoom lens and the fourth lens unit satisfy the following conditional expression when the amounts of movement during zooming are M2 and M4, respectively.
0.8 <Z2 / Z <1.1
0.9 <M2 / M4 <1.6
0.4 <M2 / (ft-fw) <1.0 The zoom lens according to claim 10 , wherein the following conditional expressions are satisfied when the focal lengths of the second lens group and the fourth lens group are f2 and f4, respectively.
0.4 <f2 / f4 <0.8 The zoom lens according to claim 1, wherein the following conditional expression is satisfied, where ft is a focal length of the entire system at the telephoto end, and f3 and f4 are focal lengths of the third lens group and the fourth lens group, respectively.
1.0 <| f1 | / (fw · ft) ^1/2 <1.6
0.6 <| f3 | / (fw · ft) ^1/2 <1.2
1.1 <f4 / (fw · ft) ^1/2 <1.8
1.5 <f5 / (fw · ft) ^1/2 <3.0 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied when the Abbe number of the third lens group is ν 3.
ν3> 55 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied when an average Abbe number of the negative lens included in the first lens group is ν1n.
ν1n> 60 A projection apparatus comprising: the zoom lens according to any one of claims 1 to 14 ; and a display body having a display surface, wherein the image displayed on the display surface is enlarged and projected onto a screen.

Images