JP2018194619A - Projection zoom lens and image projection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new zoom lens for projection. SOLUTION: The zoom lens for projection is arranged on the most magnified side and has a first lens group having a negative refractive force, and the first lens group is sequentially arranged from the magnified conjugate side to the reduced conjugate side. It has one sub-lens group, a second sub-lens group having a negative refractive force, and a third sub-lens group having a positive refractive force, and the first lens group is fixed when zooming is performed. When focusing is performed, the first sub-lens group, the second sub-lens group, and the third sub-lens group can move independently on the optical axis, and the third sub-lens group can be moved independently. A zoom lens for projection, characterized in that the distance between the first sub-lens group and the second sub-lens group changes as the lens moves on the optical axis. [Selection diagram] Fig. 2

Description

  The present invention relates to a projection zoom lens and an image projection apparatus.

  An image projection apparatus such as a projector that projects an image onto a screen or the like is known.

In such an image projection apparatus, a so-called zooming configuration is known in which zooming is performed from the wide-angle end to the telephoto end in order to change the size of the displayed image.
When performing such zooming, it is known that various optical parameters including a focal length change to cause aberration fluctuation.

  A projection zoom lens provided in an image projection apparatus is required to have a configuration in which such aberration fluctuation is suppressed and aberration correction is appropriately performed.

  An object of the present invention is to realize a novel projection zoom lens.

  The projection zoom lens according to the present invention is a projection zoom lens having a first lens group that is disposed closest to the enlargement side and has negative refractive power, and the first lens group extends from the enlargement conjugate side to the reduction conjugate side. The first sub-lens group, the second sub-lens group having a negative refractive power, and the third sub-lens group having a positive refractive power in order toward the zoom lens. When the first lens group performs zooming The first sub-lens group, the second sub-lens group, and the third sub-lens group can move independently on the optical axis when performing focusing, and the third sub-lens group can move independently on the optical axis. As the sub lens group moves on the optical axis, the distance between the first sub lens group and the second sub lens group changes.

  According to the present invention, a novel projection zoom lens capable of appropriately correcting aberrations can be realized.

It is a figure for demonstrating an example of embodiment of an imaging device. 3 is a diagram for explaining a projection zoom lens according to Embodiment 1. FIG. 6 is a diagram for explaining a projection zoom lens according to Embodiment 2. FIG. FIG. 6 is a diagram for explaining a projection zoom lens according to Example 3; FIG. 10 is a diagram for explaining a projection zoom lens according to Example 4; FIG. 10 is a diagram for explaining a projection zoom lens according to Example 5; FIG. 10 is a diagram for explaining a projection zoom lens according to Example 6; FIG. 10 is a diagram for explaining a projection zoom lens according to Example 7; FIG. 6 is a diagram illustrating an example of an operation during focusing of the projection zoom lens according to the first exemplary embodiment. FIG. 3 is an example of a longitudinal aberration diagram at a wide angle end of the projection zoom lens of Example 1; FIG. 4 is an example of a lateral aberration diagram at the wide-angle end of the projection zoom lens according to Example 1; FIG. 4 is an example of a longitudinal aberration diagram at a telephoto end of the projection zoom lens according to Example 1; FIG. 3 is an example of a lateral aberration diagram at the telephoto end of the projection zoom lens according to Example 1; 6 is an example of a longitudinal aberration diagram at the wide-angle end of the projection zoom lens of Example 2. FIG. 6 is an example of a lateral aberration diagram at the wide-angle end of the projection zoom lens of Example 2. FIG. 6 is an example of a longitudinal aberration diagram at a telephoto end of a projection zoom lens according to Example 2. FIG. 6 is an example of a lateral aberration diagram at a telephoto end of a projection zoom lens according to Example 2. FIG. FIG. 10 is an example of a longitudinal aberration diagram at the wide-angle end of the projection zoom lens according to Example 3; FIG. 10 is an example of a lateral aberration diagram at the wide-angle end of the projection zoom lens according to Example 3; 6 is an example of a longitudinal aberration diagram at a telephoto end of a projection zoom lens according to Example 3. FIG. 6 is an example of a lateral aberration diagram at a telephoto end of a projection zoom lens according to Example 3. FIG. FIG. 10 is an example of a longitudinal aberration diagram at the wide-angle end of the projection zoom lens according to Example 4; FIG. 10 is an example of a lateral aberration diagram at the wide-angle end of the projection zoom lens according to Example 4; FIG. 10 is an example of a longitudinal aberration diagram at a telephoto end of a projection zoom lens according to Example 4; FIG. 10 is an example of a lateral aberration diagram at the telephoto end of the projection zoom lens according to Example 4; FIG. 10 is an example of a longitudinal aberration diagram at the wide-angle end of the projection zoom lens according to Example 5; FIG. 10 is an example of a lateral aberration diagram at the wide-angle end of the projection zoom lens according to Example 5. FIG. 10 is an example of a longitudinal aberration diagram at a telephoto end of a projection zoom lens according to Example 5; FIG. 10 is an example of a lateral aberration diagram at the telephoto end of the projection zoom lens according to Example 5; FIG. 10 is an example of a longitudinal aberration diagram at the wide-angle end of the projection zoom lens according to Example 6; FIG. 10 is an example of a lateral aberration diagram at the wide-angle end of the projection zoom lens according to Example 6; FIG. 10 is an example of a longitudinal aberration diagram at a telephoto end of a projection zoom lens according to Example 6; FIG. 10 is an example of a lateral aberration diagram at the telephoto end of a projection zoom lens according to Example 6; 10 is an example of a longitudinal aberration diagram at the wide-angle end of the projection zoom lens of Example 7. FIG. FIG. 10 is an example of a lateral aberration diagram at the wide-angle end of the projection zoom lens according to Example 7. 10 is an example of a longitudinal aberration diagram at a telephoto end of a projection zoom lens in Example 7. FIG. 10 is an example of a lateral aberration diagram at the telephoto end of a projection zoom lens according to Example 7. FIG.

FIG. 1 shows an image projection apparatus 100 including a projection lens group 1 as a projection zoom lens, as an example of an embodiment of the present invention.
The image projection apparatus 100 in this embodiment is a projector that projects an enlarged original image displayed on a liquid crystal panel 101 as an image display element onto a screen 104 as a projection surface.

  The projector that displays the original image on the liquid crystal panel 101 combines the three lights modulated by the three liquid crystal panels 101 corresponding to the three primary colors (red, green, and blue) by the prism 102 that is a color combining optical system. The light enters the projection lens 1.

In the present embodiment, the liquid crystal panel 101 is used as an image display element for an original image. However, the present invention is not limited to this configuration, and may be performed by a reflective display element such as a DMD configured by arranging micromirrors. .
In the configuration using such a reflective display element, it is necessary to secure an optical path for illuminating the reflective display element between the reflective display element and the projection lens 1.

The projection lens group 1 is a lens system that generally enlarges and projects an original image displayed in a small size, and is a zoom lens that can project an original image with a variable magnification.
In FIG. 1, the projection lens group 1 includes, in order from the enlargement side, the first lens group 1G, the second lens group 2G, the third lens group 3G, the aperture stop S, the fourth lens group 4G, A projection optical system having a five-group configuration having five lens groups 5G.
The specific configuration of the embodiment of the present invention is illustrated in FIGS. 2 to 8, the left side of the figure is the enlargement side (enlargement conjugate side), and the right side of the figure is the reduction side (reduction conjugate side). Moreover, in order to avoid complication, the code | symbol is shared in FIGS.

  2 to 8, (a) is a zooming wide-angle end (Wide), and (b) is a zooming telephoto end (Tele).

As shown in FIGS. 2A and 2B, the first lens group G1 includes a first sub-lens group 1a, a second sub-lens group 1b having negative refractive power, and positive refraction, in order from the magnification side. And a third sub lens group 1c having power.
The first lens group G1 is fixed during zooming shown in FIGS. 2A and 2B, and has a negative refractive power as a whole in the first lens group G1.

The first lens group G1 is installed so that each of the first sub-lens group 1a, the second sub-lens group 1b, and the third sub-lens group 1c can move independently during focusing, which will be described later. Yes.
During such focusing, the third sub lens group 1c moves on the optical axis, and the distance between the first sub lens group 1a and the second sub lens group 1b changes.
At this time, most preferably, for example, the second sub lens group 1b moves on the optical axis in accordance with the movement of the third sub lens group 1c on the optical axis in a state where the first sub lens group 1a is fixed, for example. Thus, the interval between the first sub lens group 1a and the second sub lens group 1b changes.
The configuration is not limited to such a configuration, and all three sub lens groups may operate.

The first sub-lens group 1a may be set in accordance with a desired design value for either positive refractive power or negative refractive power, but the first sub-lens group 1a and the second sub-lens group 1b are combined. Then, it is desirable to set so as to have negative refractive power.
In this way, by adopting a configuration that becomes negative / positive in order from the enlargement side in the focusing group, the aberration that occurs when the distance fluctuates is corrected.
In addition, as the third sub lens group 1c moves and the distance between the first sub lens group 1a and the second sub lens group 1b also changes, the aberration is corrected more effectively.

Further, the focal length _{f 1b} of the second sub-lens group 1b, the focal length _{f 1c} of the third sub-lens group 1c, satisfy the condition (1).

By satisfying the conditional expression (1), the aberration is corrected more effectively.
When the upper limit of the conditional expression is exceeded, it indicates that the negative refractive power of the second sub lens group 1b is too strong compared to the positive refractive power of the third sub lens group 1c. While this works advantageously, it is difficult to correct distortion such as an increase in distortion, curvature of field, and astigmatism.
When the lower limit of conditional expression (1) is exceeded, it indicates that the negative refractive power of the second sub-lens group 1b is too weak compared to the positive refractive power of the third sub-lens group 1c. While it is easy to correct aberrations such as surface curvature and astigmatism, it is difficult to achieve a wide angle, which is not desirable.

In this embodiment, as shown in FIG. 9, when focusing from the long distance side to the short distance side, the distance between the second sub lens group 1b and the third sub lens group 1c varies so as to increase. In FIG. 9, the movement distance is exaggerated for the purpose of clarifying the movement in particular, but the actual movement amount is as a numerical example described later.
When the object point fluctuates from the long distance side to the short distance side, the angle of view changes in a narrowing direction, and the image plane easily curves in the over direction. Therefore, in order to correct field curvature due to object point fluctuation, it is necessary to widen the distance between the first sub lens group 1a and the second sub lens group 1b.

Although the curvature of field can be corrected by widening the distance between the first sub lens group 1a and the second sub lens group 1b, the distance between the first sub lens group 1a and the second sub lens group 1b is simply corrected. Since the in-focus position changes only by spreading out, the third sub-lens group 1c is moved to correct the in-focus position.
At that time, in the first lens group G1 having a negative refractive power, as is apparent from the formula (1), the third sub lens group 1c has a refractive power in the first lens group G1 under the strong negative power control as a whole. Is relatively weak, it is necessary to increase the amount of movement.
As a result, the movement amount of the third sub lens group 1c for correcting the in-focus position is larger than the movement amount of the second sub lens group 1b for image plane correction, and the second sub lens group 1b and the third sub lens group 1b The distance from the sub lens group 1c changes in the direction in which it increases.

Therefore, in the present embodiment, when focusing from the long distance side to the short distance side, it is desirable that the distance between the second sub lens group 1b and the third sub lens group 1c be varied.
With such a configuration, it is possible to appropriately correct aberration while suppressing the variation of the in-focus position while correcting the curvature of field caused by the variation of the object point from the long distance side to the short distance side.

Further, in the present embodiment, the focal length f _1G of the first lens group 1G, the focal length fw of the entire system at the wide-angle end satisfies the conditional expression (2).

When the upper limit of conditional expression (2) is exceeded, the negative refractive power of the first lens group 1G becomes strong, which is advantageous for achieving a wide angle, but distortion becomes large and correction is difficult.
When the lower limit value of conditional expression (2) is exceeded, the negative refractive power of the first lens group becomes weak, and it becomes difficult to achieve widening while making it easy to correct aberrations such as distortion.
The focal length f _1G of the first lens group 1G, by keeping within the range of the conditional expression according to the focal length fw of the entire system at the wide angle end (2), while achieving a wide angle of the lens system, aberrations properly Can be corrected.

  In the present embodiment, the focal length f1b of the second sub-lens group included in the first lens group 1G and the focal length f1c of the third sub-lens group are relative to the focal length fw of the entire system at the wide angle end. The following conditional expressions (3) and (4) are satisfied.

Conditional expression (3) indicates the relationship between the focal length of the second sub lens group 1b having negative refractive power in the first lens group 1G and the focal length of the entire system.
When the upper limit value of conditional expression (3) is exceeded, the negative refractive power of the first lens group 1G becomes weak, and field curvature and astigmatism become advantageous, but it is difficult to widen the angle.
When the lower limit is exceeded, the negative refractive power of the entire first lens group 1G becomes strong, which is advantageous for widening the angle, but it is difficult to correct distortion.

Conditional expression (4) shows the relationship between the focal length of the third sub lens group 1c having positive refractive power in the first lens group 1G and the focal length of the entire system.
If the upper limit value of conditional expression (4) is exceeded, the positive refractive power of the first lens group 1G will be weakened, it will be difficult to correct distortion, and the amount of movement during focusing will increase, resulting in structural freedom. The problem of becoming smaller can arise. On the other hand, the condition of the curvature of the positive lens becomes loose, and it becomes easy to suppress coma.
When the lower limit of conditional expression (4) is exceeded, the positive refractive power of the first lens group 1G becomes strong, and it becomes easy to correct field curvature and astigmatism, but it is difficult to widen the angle.

In the present embodiment, the first lens group 1G has at least one aspheric lens.
With this configuration, distortion and coma caused by widening of the angle are corrected with higher accuracy.

  In the present embodiment, the position of each lens is adjusted while the first sub lens group 1a is fixed during focusing. That is, at least one of the plurality of lens groups included in the first lens group 1G has a fixed sub lens group.

  With this configuration, the structure of the lens barrel is facilitated and the degree of freedom is improved.

In the present embodiment, the average value N _dave1G of the refractive index of the spherical lens having negative refractive power constituting the first lens group 1G satisfies the conditional expression (5).

Conditional expression (5) represents the relationship of the refractive index of the negative lens, and is related to widening of the angle and Petzval sum.
When the upper limit of conditional expression (5) is exceeded, the refractive index of the negative lens increases, which is advantageous for widening the angle, and the radius of curvature can be suppressed and the occurrence of coma aberration can be suppressed, but the Petzval sum is disadvantageous. .
Further, when the lower limit of conditional expression (5) is exceeded, the Petzval sum can be suppressed within a predetermined range, and curvature of field and astigmatism can be suppressed to be small. Since the radius is tight, it is difficult to correct aberrations such as coma.
_{Designed so} that the average value N _dave1G of the refractive index of the spherical lens having negative refractive power falls within the range of the conditional expression (5), distortion and coma caused by _widening of the angle can be improved with higher accuracy. It is corrected.

In this embodiment, the average Abbe number ν _d1G of the spherical lenses having negative refractive power constituting the first lens group 1G satisfies the conditional expression (6).

  Conditional expression (6) is a condition for suppressing fluctuations in the chromatic aberration of magnification due to focusing. When the lower limit is exceeded, the overall Abbe number in the first lens group 1G becomes small. Is difficult to suppress, and chromatic aberration of magnification increases.

  Specific configuration examples of the projection lens 1 as described above are shown in Tables 1 to 35 as numerical values in Examples 1 to 7. In addition, aberration diagrams in Examples 1 to 7 are shown in FIGS.

Each of Examples 1 to 7 is a numerical example that satisfies the conditional expression (1) already described. In addition to conditional expression (1), any or all of conditional expressions (2) to (6) are satisfied, but the present invention is not limited to this configuration.
In Examples 1 to 7, the following symbols are used.
R: radius of curvature D: surface spacing Nd: refractive index νd: Abbe number f: focal length of the entire system ω: half angle of view

[Numerical Example 1]
The lens configurations of Example 1 are shown in Tables 1 to 5.

  Moreover, the surface displacement of each aspherical surface described in Table 5 follows the following mathematical formula.

[Numerical Example 2]
The lens configurations of Example 2 are shown in Tables 6 to 10.

[Numerical Example 3]
The lens configurations of Example 3 are shown in Tables 11 to 15.

[Numerical Example 4]
The lens configurations of Example 4 are shown in Tables 16 to 20.

[Numerical Example 5]
Tables 21 to 25 show lens configurations of Example 5.

[Numerical Example 6]
Table 26 to Table 30 show lens configurations of Example 6.
In this embodiment, as is clear from Table 26, the first sub lens group 1a and the third sub lens group 1c operate on the lens optical axis during focusing, and the second sub lens group 1b is fixed. Is done.

[Numerical Example 7]
Tables 31 to 35 show lens configurations of Example 7.

10 to 37 show aberration diagrams of the seven projection lenses 1 shown as examples.
10 to 13 related to Example 1, FIG. 10 shows a longitudinal aberration diagram at the wide-angle end, and FIG. 11 shows a lateral aberration diagram at the wide-angle end. 12 shows a longitudinal aberration diagram at the telephoto end, and FIG. 13 shows a lateral aberration diagram at the telephoto end.
In the spherical aberration diagram, symbols R, G, and B represent aberration curves for the corresponding wavelengths (R = 620 nm, G = 550 nm, B = 460 nm).

  14 to 17 relating to Example 2, FIG. 14 shows a longitudinal aberration diagram at the wide-angle end, and FIG. 15 shows a lateral aberration diagram at the wide-angle end. FIG. 16 shows a longitudinal aberration diagram at the telephoto end, and FIG. 17 shows a lateral aberration diagram at the telephoto end.

  18 to 21 relating to Example 3, FIG. 18 shows a longitudinal aberration diagram at the wide-angle end, and FIG. 19 shows a lateral aberration diagram at the wide-angle end. FIG. 20 shows a longitudinal aberration diagram at the telephoto end, and FIG. 21 shows a lateral aberration diagram at the telephoto end.

  22 to 25 relating to Example 4, FIG. 22 shows a longitudinal aberration diagram at the wide-angle end, and FIG. 23 shows a lateral aberration diagram at the wide-angle end. FIG. 24 shows a longitudinal aberration diagram at the telephoto end, and FIG. 25 shows a lateral aberration diagram at the telephoto end.

  26 to 29 related to Example 5, FIG. 26 shows a longitudinal aberration diagram at the wide-angle end, and FIG. 27 shows a lateral aberration diagram at the wide-angle end. FIG. 28 shows a longitudinal aberration diagram at the telephoto end, and FIG. 29 shows a lateral aberration diagram at the telephoto end.

  30 to 33 relating to Example 6, FIG. 30 shows a longitudinal aberration diagram at the wide angle end, and FIG. 31 shows a lateral aberration diagram at the wide angle end. FIG. 32 shows a longitudinal aberration diagram at the telephoto end, and FIG. 33 shows a lateral aberration diagram at the telephoto end.

  34 to 37 relating to Example 7, FIG. 34 shows a longitudinal aberration diagram at the wide angle end, and FIG. 35 shows a lateral aberration diagram at the wide angle end. FIG. 36 shows a longitudinal aberration diagram at the telephoto end, and FIG. 37 shows a lateral aberration diagram at the telephoto end.

As shown in the aberration diagrams of each example, the aberration is corrected at a high level in each example, and a change in field curvature due to focusing is also suppressed.
The spherical aberration changes with focusing, but the amount of change is sufficiently small as an absolute value.

  On-axis chromatic aberration and lateral chromatic aberration are small, coma and disturbance of the color difference are well suppressed up to the outermost periphery, and distortion is corrected sufficiently small.

  In other words, each of the projection lenses 1 of Examples 1 to 7 is a high-performance projection zoom lens in which various aberrations are sufficiently reduced and a change in performance due to focusing is small.

  According to the present invention, a novel projection zoom lens and an image projection apparatus using the same can be realized.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described configuration, and various configurations can be made within the scope of the gist of the invention described in the claims. Is possible.

  The effects described in the embodiments of the present invention are merely a list of suitable effects resulting from the invention, and the effects of the present invention are not limited to those described in the embodiments.

1G first lens group
DESCRIPTION OF SYMBOLS 1a 1st sub lens group 1b 2nd sub lens group 1c 3rd sub lens group S Diaphragm 2G 2nd lens group
3G 3rd lens group 4G 4th lens group 5G 5th lens group 6G 6th lens group 1 Projection lens (zoom lens for projection)
100 Imaging device
104 screen (projection surface)

Japanese Patent No. 6027453 Japanese Patent No. 5026929 Japanese Patent No. 5537110 Japanese Patent No. 5006113

Claims (10)

A zoom lens for projection having a first lens group disposed on the most magnified side and having negative refractive power,
The first lens group includes, in order from the magnification conjugate side toward the reduction conjugate side, a first sub lens group, a second sub lens group having a negative refractive power, and a third sub lens group having a positive refractive power. Have
The first lens group is fixed when zooming, and the first sub-lens group, the second sub-lens group, and the third sub-lens group are independently optical axes when performing focusing. Move on,
A projection zoom lens, wherein the third sub-lens group moves on an optical axis, and an interval between the first sub-lens group and the second sub-lens group changes. The projection zoom lens according to claim 1,
The focal length f _1b of the second sub lens group and the focal length f _1c of the third sub lens group are conditional expressions:
(1) −0.5 <f _1b / f _1c <−0.1
Projection zoom lens characterized by satisfying The projection zoom lens according to claim 1 or 2,
A projection zoom lens, wherein when performing focusing from a long distance side to a short distance side, the distance between the second sub lens group and the third sub lens group changes in a widening direction. The projection zoom lens according to any one of claims 1 to 3,
The focal length f _1G of the first lens group and the focal length fw of the entire system at the wide angle end in the zooming are conditional expressions:
(2) -3.0 _{<f 1G} /fw<-1.5
Projection zoom lens characterized by satisfying The projection zoom lens according to any one of claims 1 to 4,
The focal length f _1b of the second sub-lens group, the focal length f _1c of the third sub-lens group, and the focal length fw of the entire system at the wide-angle end in zooming are conditional expressions (3) -2.0 <F _1b /fw<−0.5
(4) 3.0 <f _1c /fw<9.0
Projection zoom lens characterized by satisfying The projection zoom lens according to any one of claims 1 to 5,
A zoom lens for projection, wherein the first lens group includes at least one aspheric lens. The projection zoom lens according to any one of claims 1 to 6,
A projection zoom lens, wherein at least one of the sub-lens groups constituting the first lens group is fixed during the focusing. The projection zoom lens according to any one of claims 1 to 7,
The first lens group includes a spherical lens having at least one negative refractive power;
The average value of the refractive index N _{dave — 1G} of the spherical lens having negative refractive power is the conditional expression (5) 1.55 <N _{dave — 1G} <1.75
Projection zoom lens characterized by satisfying A projection zoom lens according to any one of claims 1 to 8,
The first lens group includes a spherical lens having at least one negative refractive power;
The average Abbe number ν _{d1ave_1G} of the spherical lens having negative refractive power is the conditional expression (6) 45.0 <ν _{d1ave_1G}
Projection zoom lens characterized by satisfying   An image projection apparatus comprising the projection zoom lens according to claim 1.

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