JP6124639B2 - Zoom lens and image projection apparatus having the same - Google Patents

Description

  The present invention relates to a zoom lens, and is suitable as a projection optical system used in an image projection apparatus (projector) that magnifies and projects an image displayed on an image display element.

  Since the image projection apparatus can project an image of a personal computer or a video on a large screen, it is used in various scenes such as a presentation and a meeting. A projection optical system used in an image projection apparatus is required to be a zoom lens capable of projecting an entire image formed on an image display element on a screen surface with various projection magnifications and high resolution.

  There are a mechanical correction type and an optical correction type as a zoom method of a general zoom lens. The mechanical correction type includes a variator group responsible for zooming and a compensator group responsible for correcting an image plane that moves due to zooming. On the other hand, in the optical correction formula, only the variator group moves linearly during zooming. In this zoom lens, the use range of the power balance (refractive power arrangement) and lateral magnification of each lens group is set to an appropriate value.

  When a zoom lens using an optical correction formula is used in an image projection apparatus, the maximum value of the image plane movement amount (hereinafter referred to as intermediate focus movement amount Δsk) that occurs during zooming falls within an allowable depth as a projection image. . When the optical correction formula is used in the zoom lens, the lens configuration can be simplified compared to the mechanical correction formula.

  Specifically, a zoom lens can be configured without using a cam ring in which a nonlinear cam groove is formed. Conventionally, a zoom lens for an image projection apparatus using an optical correction formula is known (Patent Document 1). In Patent Document 1, a zoom lens including first to fifth lens units having negative, positive, negative, positive, and positive refractive powers in order from an enlargement conjugate side that is a screen side to a reduction conjugate side that is an image display element side. Is disclosed.

  During zooming, the second lens group and the fourth lens group are linearly moved together (in the same locus). This zoom lens does not require a cam ring having a non-linear cam groove because both of the two moving lens groups are moved together during zooming.

  On the other hand, as a zoom lens for an image projection apparatus using a mechanical correction formula, from the first lens group to the fifth lens group having negative, positive, negative, positive, and positive refractive powers in order from the magnification conjugate side to the reduction conjugate side. A five-group zoom lens is known (Patent Documents 2 and 3). Patent Documents 2 and 3 disclose zoom lenses in which the second to fourth lens groups are moved to the magnification conjugate side during zooming from the wide-angle end to the telephoto end.

Japanese Patent Publication No. 40-23076 JP 2007-206420 A JP 2007-225877 A

  In an optical correction type zoom lens, the lens group linearly moves during zooming. For this reason, a non-linear cam is not required, and the lens barrel is simplified. However, the image planes coincide at the time of zooming only in two zooming positions in the zooming range, and do not match in other zooming ranges. At this time, the amount of intermediate focus movement that is a mismatch amount is large. For example, if the allowable range as the projection image of the image projection apparatus is not within the allowable range, it cannot be used in the deviating magnification range. For this reason, in order to construct an optical correction type zoom lens, it is important to specify the zoom type and the refractive power arrangement so that the intermediate focus movement amount is small.

  In particular, in the zoom lens using the optical correction formula including the first lens unit to the fifth lens unit having negative, positive, negative, positive, and positive refractive powers in order from the magnification conjugate side to the reduction conjugate side, the zoom lens moves upon zooming. The selection of the lens group to be performed and the refractive power of the lens group are important. If the selection of the lens group at this time or the refractive power of the selected lens group is inappropriate, the amount of intermediate focus movement increases, making it difficult to obtain good optical performance over a wide zoom range.

  The present invention provides a zoom lens that has a simple configuration using an optical correction formula, has a small amount of intermediate focus movement, and easily obtains good optical performance over a wide zoom range, and an image projection apparatus using the zoom lens. Objective.

The zoom lens of the present invention includes, in order from the magnification conjugate side to the reduction conjugate 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, and a positive refraction. A fourth lens group having a positive power and a fifth lens group having a positive refractive power, and the second lens group and the fourth lens group move toward the magnification conjugate side along the same locus upon zooming from the wide-angle end to the telephoto end. In a zoom lens that moves and the first lens group, the third lens group, and the fifth lens group do not move, a combination of the second lens group, the third lens group, and the fourth lens group at the wide-angle end When the focal length is f2 to 4w, the lateral magnification of the fifth lens group at the wide angle end is β5w, and the focal length of the entire system at the wide angle end is fw,
6.0 ≦ f2-4w / fw <10.0
0.05 <β5w <0.30
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a zoom lens that has a simple configuration using an optical correction formula, has a small amount of intermediate focus movement, and can easily obtain good optical performance over a wide zoom range.

(A), (B) Lens cross-sectional views at the wide-angle end and the telephoto end of Embodiment 1 of the present invention (A), (B) Aberration diagrams at the wide-angle end and the telephoto end at a projection distance of 2100 mm when the zoom lens of Numerical Example 1 is expressed in mm. (A), (B) Lens cross-sectional view at the wide-angle end and the telephoto end of the second embodiment of the present invention (A), (B) Aberration diagrams at the wide-angle end and the telephoto end at a projection distance of 2100 mm when the zoom lens of Numerical Example 2 is expressed in mm. (A), (B) Lens cross-sectional views at the wide-angle end and the telephoto end of Embodiment 3 of the present invention (A), (B) Aberration diagrams at the wide-angle end and the telephoto end at a projection distance of 2100 mm when the zoom lens of Numerical Example 3 is expressed in mm. Schematic diagram of main parts of the image projection apparatus of the present invention

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The zoom lens of the present invention includes, in order from the magnification conjugate side to the reduction conjugate 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, and a positive refraction. A fourth lens group having a positive power and a fifth lens group having a positive refractive power. During zooming, the second lens group and the fourth lens group move along the same locus, and the first lens group, the third lens group, and the fifth lens group do not move.

  The zoom lens of the present invention uses an optical correction formula in which the second lens group and the fourth lens group move linearly together during zooming. Particularly at the time of zooming from the wide-angle end to the telephoto end, the second lens group and the fourth lens group move to the magnification conjugate side.

  FIGS. 1A and 1B are lens cross-sectional views at the wide-angle end (short focal length end) and the telephoto end (long focal length end) of Embodiment 1 of the zoom lens according to the present invention. 2A and 2B, the projection distance (distance from the first lens surface) of the zoom lens of Example 1 is 2100 mm (the distance when the numerical example is expressed in mm, the same applies hereinafter). FIG. 6 is a longitudinal aberration diagram at the wide-angle end and at the telephoto end at that time.

  3A and 3B are lens cross-sectional views at the wide-angle end and the telephoto end of the second embodiment of the zoom lens according to the present invention. 4A and 4B are longitudinal aberration diagrams at the wide-angle end and the telephoto end when the projection distance of the zoom lens of Example 2 is 2100 mm, respectively.

  5A and 5B are lens cross-sectional views at the wide-angle end and the telephoto end of Embodiment 3 of the zoom lens according to the present invention. 6A and 6B are longitudinal aberration diagrams at the wide-angle end and the telephoto end when the projection distance of the zoom lens of Example 3 is 2100 mm, respectively.

  FIG. 7 is a schematic diagram of a main part of an image projection apparatus (projector) having the zoom lens of the present invention. The zoom lens of each embodiment is a projection lens (projection optical system) used in an image projection apparatus (projector). In the lens cross-sectional view, the left side is the screen, and the right side is the projected image side (image display element side). In the lens cross-sectional view, LA is a zoom lens.

  i indicates the order of the lens groups from the object side, and Bi is the i-th lens group. SP is an aperture stop. IP corresponds to an original image (projected image) such as a liquid crystal panel (image display element). In this embodiment, an image display element for forming an original image is arranged. S is the screen surface. PR is an optical block corresponding to a prism for color separation and color synthesis, an optical filter, a face plate (parallel plate glass), a quartz low-pass filter, an infrared cut filter, and the like.

  The arrows indicate the movement direction (movement locus) of the lens group during zooming from the wide-angle end to the telephoto end. The wide-angle end and the telephoto end are zoom positions when the zooming lens units are positioned at both ends of a range in which the zoom lens group can move on the optical axis. In each example, the zoom lens in order from the magnification conjugate side to the reduction conjugate side is 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, and a positive refraction. It consists of a fourth lens group having a positive power and a fifth lens group having a positive refractive power. The first, third, and fifth lens groups do not move during zooming, and the second and fourth lens groups move linearly together during zooming.

  In the spherical aberration diagram, the solid line has a wavelength of 620 nm. In the astigmatism diagram, the dotted line indicates the meridional image plane, and the solid line indicates the sagittal image plane. Fno is the F number, and Y is the image height. In the aberration diagrams, spherical aberration is drawn on a scale of 0.2 mm, astigmatism is drawn on a scale of 0.2 mm, and distortion is drawn on a scale of 1.0%.

In the zoom lens of each embodiment, the combined focal length of the second lens unit B2, the third lens unit B3, and the fourth lens unit B4 at the wide angle end is set to f2 to 4w. The lateral magnification of the fifth lens unit B5 at the wide angle end is β5w, and the focal length of the entire system at the wide angle end is fw. At this time,
6.0 ≦ f2-4w / fw <10.0 (1)
0.05 <β5w <0.30 (2)
The following conditional expression is satisfied.

  Next, the technical meaning of conditional expressions (1) and (2) will be described. In the five-unit zoom lens of each example, the intermediate focus movement amount Δsk of the entire system is β5, the second, third, and fourth lens groups (hereinafter “magnification”) of the fifth lens group that is the final lens group. The intermediate focus movement amount Δsk generated in the “lens group” is assumed to be Δsk2-4. Then, it can be expressed by the following formula.

Δsk = β52 * Δsk2-4
The allowable depth Δ of the projector can be expressed by the following equation, where FNO of the projection lens to be used is FNO and the pixel pitch length of the image display element to be used is p (μm).

Δ = FNO * p * 1.4 (μm)
With a general optical correction zoom lens,
Δsk ≦ Δ
It is necessary to.

  In order to obtain a lateral magnification β5 in which the intermediate focus movement amount Δsk is within an allowable range, the combined focal lengths of the second, third, and fourth lens groups (magnification lens groups) are f2 to 4w, and the wide angle end of the entire system. Let fw be the focal length. At this time, it is desirable that the combined focal lengths f2 to 4w satisfy the conditional expression (1). In addition, it is desirable to set the lateral magnification β5w at the wide angle end of the fifth lens unit L5, which is the lens unit closest to the reduction conjugate side, within the range of the conditional expression (2).

  If the lower limit of conditional expression (1) is exceeded and the combined focal length of the variable power lens unit is shortened, the focal length of each lens unit of the variable power lens unit is also shortened, and aberrations associated with variable power increase. Aberration correction becomes difficult. If the combined focal length of the variable power lens unit becomes too long beyond the upper limit value, the focal length of each lens unit of the variable power lens unit also increases, and the amount of movement during zooming increases, and the entire lens becomes larger. Increase in size. In conditional expression (2), it is effective to make the lateral magnification of the final lens group as small as possible within the range where the optical specifications are satisfied in order to satisfactorily correct the optical performance with the intermediate focus fluctuation sufficiently small. It is the one that paid attention.

  If the lower limit value of the conditional expression (2) is exceeded and the value of the lateral magnification β5w becomes too small, the combined focal length of the variable power lens unit must be increased, and thereby the focal point of each lens unit of the variable power lens unit. The distance also becomes longer. As a result, the amount of movement during zooming becomes large, the entire lens becomes large, and it becomes difficult to obtain a sufficiently long back focus. Also, if the lateral magnification β5w increases beyond the upper limit, it becomes difficult to compress the intermediate focus movement amount Δsk, and the intermediate focus movement amount Δsk of the entire lens generated by zooming becomes larger with respect to the allowable depth. Absent. More preferably, the numerical ranges of conditional expressions (1) and (2) are set as follows.

6.1 <f2-4w / fw <9.0 (1a)
0.10 <β5w <0.26 (2a)
As described above, according to each embodiment, using an optical correction type zoom lens that does not require a non-linear cam, the focus variation (hereinafter referred to as intermediate focus variation (Δsk)) due to zooming is sufficiently small with respect to the allowable depth. A zoom lens with good optical performance can be obtained. In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions.

  L is the total optical length (distance from the most magnified conjugate side lens surface vertex to the most reduced conjugate side lens surface vertex), and from the most magnified conjugate side lens surface of the first lens unit B1 to the object side of the first lens unit B1. Let the distance to the principal point be dL. The first lens unit B1 is composed of three negative lenses and one positive lens in order from the magnification conjugate side to the reduction conjugate side, and the distance between the negative lens on the most reduction conjugate side and the positive lens is 1d. At this time, it is preferable to satisfy one or more of the following conditional expressions.

0.5 <(dL−L) / L <2.0 (3)
0.1 <1d / L <0.4 (4)
By setting the object point position of the first lens unit L1 to the enlargement conjugate side, the focal length of the second lens unit L2 can be increased, and the refractive power can be reduced. Therefore, in the second lens group and subsequent lens groups, it is only necessary to gently bend the light beam, so that the refractive power can be reduced.

  If the lower limit value of conditional expression (3) is deviated, the refractive power of the second lens unit B2 must be increased, and the refractive power of the variable power lens unit becomes too strong, which makes it difficult to correct aberrations. If the upper limit of the conditional expression (3) is deviated, the refractive power of the second lens unit B2 must be weakened, so that the combined focal length of the variable power lens unit becomes too large, thereby causing each variable power lens unit. The focal length is also increased. As a result, the amount of movement of the second lens unit B2 and the fourth lens unit B4 during zooming increases, and the entire system increases in size.

  If the lower limit of conditional expression (4) is deviated, the reduction-side principal point position of the first lens unit B1 does not move sufficiently to the enlargement side, so that the refractive power of the variable-power lens unit becomes too strong and aberration correction is difficult. become. If the upper limit of the conditional expression (4) is deviated, the combined focal length of the variable power lens unit must be increased, thereby increasing the focal length of each variable power lens unit. As a result, the amount of movement of the second lens unit B2 and the fourth lens unit B4 during zooming increases, and the entire system increases in size. More preferably, the numerical ranges of conditional expressions (3) and (4) should be set as follows.

0.60 <(dL-L) / L <1.95 (3a)
0.12 <1d / L <0.35 (4a)
As described above, according to each embodiment, the focus variation caused by zooming is minimized. Then, it becomes easy to set the lateral magnification of the final lens unit to be small, and it becomes easy to sufficiently reduce the intermediate focus variation while weakening the refractive power of the variable power lens unit. Thereby, it is easy to obtain a zoom lens that corrects various aberrations in the entire zoom range with a simple configuration and has good optical performance over the entire screen.

[Example 1]
Embodiment 1 of the present invention will be described below. The first exemplary embodiment is a five-unit zoom lens including the first lens unit B1 to the fifth lens unit B5 having negative, positive, negative, positive, and positive refractive powers in order from the magnification conjugate side. At the time of zooming, the first lens unit B1, the third lens unit B3, and the fifth lens unit B5 do not move. At the time of zooming from the wide angle end to the telephoto end, the second lens unit B2 and the fourth lens unit B4 move together to the enlargement conjugate side (the same movement locus).

  In this embodiment, a stop SP is disposed on the image side of the second lens unit B2. The aperture stop SP moves integrally with the second lens unit B2 during zooming. The first lens unit B1 includes a negative lens G11, a negative lens G12, a negative lens G13, and a positive lens G14 in order from the magnification conjugate side to the reduction conjugate side.

  The second lens group B2 includes a positive lens G21, a negative lens G22, a positive lens G23, and a negative lens G24 in order from the magnification conjugate side to the reduction conjugate side. The third lens unit B3 includes a negative lens G31 and a positive lens G32 in order from the magnification conjugate side to the reduction conjugate side. The fourth lens unit B4 includes a negative lens G41, a positive lens G42, and a positive lens G43 in order from the magnification conjugate side to the reduction conjugate side. The fifth lens unit B5 includes a positive lens G51.

  By setting the interval of the positive lens G14 large with respect to the three negative lenses G11, G12, G13 of the first lens unit B1, the reduction conjugate side principal point of the first lens unit B1 is largely moved to the enlargement conjugate side. Yes. Further, by arranging a cemented lens or a positive lens and a negative lens in the second and fourth lens groups B2 and B4, the occurrence of chromatic aberration in each lens group is suppressed, and the amount of variation in chromatic aberration during zooming is reduced. Here, the stop SP represents the vicinity of the position where the off-axis principal ray intersects the optical axis, and is not limited to a physical aperture.

  By satisfying conditional expressions (1) and (2), an increase in intermediate focus fluctuation (Δsk) is reduced. Further, by satisfying the conditional expressions (3) and (4), the principal point position of the first lens unit B1 is set to the enlargement conjugate side while reducing the increase in the intermediate focus fluctuation (Δsk), and the first variable magnification is used. 2. A predetermined zoom ratio is secured while weakening the refractive power of the second lens unit B2 and the fourth lens unit B4.

[Example 2]
The number of lens groups of the zoom lens of Example 2, the refractive power of each lens group, the zoom method, and the like are the same as those of Example 1. The lens configuration of the first lens unit B1 is the same as that of the first embodiment. The second lens unit B2 includes a positive lens G21, a positive lens G22, and a negative lens G23 in order from the magnification conjugate side to the reduction conjugate side. The lens configuration of the third lens unit B3 is the same as that of the first embodiment. The fourth lens unit B4 includes a negative lens G41, a positive lens G42, and a negative lens G43 in order from the magnification conjugate side to the reduction conjugate side. The fifth lens unit B5 includes a positive lens G51 and a positive lens G52 in order from the magnification conjugate side to the reduction conjugate side.

  In this embodiment, a change in distortion aberration during zooming is reduced by providing a stop near the center of the entire lens system on the image side of the third lens unit B3 that does not move during zooming. In addition, aberration correction is satisfactorily performed by suppressing the incident height (h_) of the off-axis principal ray on the enlargement conjugate side or the reduction conjugate side.

[Example 3]
The number of lens groups of the zoom lens of Example 3, the refractive power of each lens group, the zoom method, and the like are the same as those of Example 1. The lens configuration of each lens group is the same as that of the first embodiment.

  In this embodiment, compared to the first embodiment, the principal point position of the first lens unit B1 is further set on the enlargement conjugate side. For this reason, the focal length of each variable power lens group is shortened, and the refractive power is increased. Thereby, the zoom ratio is effectively obtained.

  Next, the features of the zoom lens of the present invention will be described using the zoom lens disclosed in Patent Document 1 as an example. When the zoom lens disclosed in Patent Document 1 is applied to a projection lens for a projector, the intermediate focus movement amount Δsk occupies a value of about 80% with respect to the allowable depth of the projector. As a result, the image quality of the projected image, which is not a small value, can ensure a tolerance for design tolerances.

  The paraxial arrangement of the zoom lens of Patent Document 1 is set so that the intermediate focus movement amount Δsk of the variable power lens group is minimized. Specifically, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the focal length of the fourth lens group is f4. The lateral magnification of the second lens group at the wide angle end is β2w, the lateral magnification of the second lens group at the telephoto end is β2t, the lateral magnification of the third lens group at the wide angle end is β3w, and the lateral magnification of the third lens group at the telephoto end is Let β3t. The lateral magnification of the fourth lens group at the wide angle end is β4w, and the lateral magnification of the fourth lens group at the telephoto end is β4t. At this time, the condition for minimizing the intermediate focus movement amount Δsk can be expressed by the following equation.

f2 / f4 = 1 (1x)
β2w × β4t = 1 (2x)
β2t × β4w = 1 (3x)
f3 / f2 × √2≈−1 (4x)
β3w × β3t = 1 (5x)
The values of Expression (1x) to Expression (5x) in Numerical Example 1 of Patent Document 1 are as follows.

(Numerical example 1 of Patent Document 1)
Formula (1x) = 0.98
Formula (2x) = 1.05
Formula (3x) = 1.06
Formula (4x) = − 0.95
Formula (5x) = 1.07
In Patent Document 1, the intermediate focus movement Δsk of the variable power lens unit is suppressed to be small by setting the paraxial arrangement near the minimum condition for the intermediate focus movement amount Δsk. In Patent Document 1, it is necessary to take a paraxial arrangement near the minimum condition for the intermediate focus movement amount Δsk. For this reason, the degree of freedom of the refractive power of each variable power lens group is small. As a result, the refractive power of each variable power lens group tends to increase, and various aberrations such as spherical aberration tend to occur. . Specifically, in order to reduce the intermediate focus movement amount Δsk, the refractive power arrangements of the above-described equations (1x) to (5x) are adopted.

  Here, the expressions (1x), (2x), and (3x) are the most conjugate conjugate side at the wide-angle end and the telephoto end of the second lens group B2 having a positive refractive power and the fourth lens group B4 having a positive refractive power. Represents a condition for equalizing the sum of the distances (conjugate point intervals) between the object point located at and the image point located closest to the reduction conjugate side. Expressions (4x) and (5x) have the same conjugate point distance between the wide-angle end and the telephoto end of the third lens unit B3 having negative refractive power, and the intermediate focus movement between the second lens unit B2 and the fourth lens unit B4. This represents a condition for obtaining the intermediate focus movement amount Δsk of the third lens unit B3 having the same absolute value as the amount Δsk.

  When the second, third, and fourth lens groups B2, B3, and B4 satisfy the formulas (1x) to (5x), the magnification is generated in the second lens group B2 and the fourth lens group B4. The image plane movement and the image plane movement at the time of zooming occurring in the third lens unit B3 cancel each other out. As a result, the intermediate focus fluctuation amount Δsk is kept small.

  In Example 1 of Patent Document 1, the refractive power φn of each variable power lens group is increased as described below. The focal length and the refractive power φn (normalized by the refractive power φw at the wide-angle end) of the variable power lens group of Example 1 of Patent Document 1 are as follows.

(Example 1 of Patent Document 1)
Nth lens group: focal length: φn / φw
Second lens group: 109.04: 0.64
Third lens group: −73.00: −0.96
Fourth lens group: 111.21: 0.63
All systems: 21.60 (wide end)
On the other hand, in the zoom lens of the optical correction type according to the present invention, the lateral magnification β5 of the fifth lens unit B5 which is the final lens unit is set small as in the conditional expression (2). As a result, the intermediate focus fluctuation amount in the entire system is suppressed to be small, and the refractive power arrangement of the variable magnification lens unit is set weak by taking the refractive power arrangement deviated from the minimum condition of the intermediate focus movement amount Δsk of the variable magnification lens unit. .

  According to the present invention, the optical power of the variable power lens group is weak and good optical performance can be easily obtained while keeping the intermediate focus movement amount Δsk small. The lateral magnification β5 of the fifth lens unit B5 of Example 1 of Patent Document 1 and Example 1 of the present invention is as follows.

Horizontal Magnification: Patent Document 1: Present Invention (Example 1)
β5: 0.39: 0.21
The value of Example 1 of this invention with respect to Formula (1x)-Formula (5x) is as follows.

Formula (1x) = 1.30
Formula (2x) = 1.02
Formula (3x) = 1.01
Formula (4x) = − 0.78
Formula (5x) = 1.02
As a result, the intermediate focus movement amount Δsk is sufficiently small at 3% or less with respect to the allowable depth. In addition, as described below, the refractive power of each variable power lens group can be set to be significantly weaker than that of Patent Document 1.

The focal length and the refractive power φn (normalized by the refractive power φw at the wide end) of the variable power lens unit in Example 1 of the present invention are as follows.
Nth lens group: focal length: φn / φw
Second lens group: 112.7: 0.19
Third lens group: −62.1: −0.35
Fourth lens group: 87.0: 0.25
In each embodiment of the present invention, in order to realize the above-described refractive power arrangement, the position of the reduction conjugate side principal point of the first lens unit B1 is positioned larger on the enlargement conjugate side than the lens surface on the enlargement conjugate side of the first lens unit B1. It is configured to do.

  Specifically, the first lens unit B1 includes at least one negative lens and at least one positive lens in order from the magnification conjugate side to the reduction conjugate side. Then, by arranging them at intervals as shown in conditional expression (4), the principal point position on the reduction conjugate side is set to be larger on the magnification conjugate side than the lens surface on the magnification conjugate side of the first lens unit B1. . As a result, the object point on the magnification conjugate side of the second lens group B2 is set at a position far away from the lens surface on the magnification conjugate side of the first lens group B1 to the magnification conjugate side, thereby the focal length of the second lens group B2. Can be set longer.

  Further, when the focal length f2 of the second lens unit B2 is increased, the focal length f3 of the third lens unit B3 can be set longer due to the relationship of the formula for minimizing the intermediate focus movement amount Δsk. As a result, the focal length f4 of the fourth lens unit B4 can be set longer as the focal length f2 of the second lens unit B2 increases from the relationship of the expression (1x). As a result, the image point on the reduction conjugate side of the fourth lens group B4 is greatly moved to the reduction conjugate side, and it becomes easy to set the lateral magnification of the fifth lens group B5 as the final lens group to be small.

  In each embodiment, the second lens unit B2, the third lens unit B3, or the fourth lens unit B4 has an aperture stop. In each embodiment, the pupil position on the reduction conjugate side is located at infinity.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. As described above, according to each embodiment, the paraxial arrangement presented by the above-described means is intentionally broken from the paraxial arrangement in which the intermediate focus movement amount Δsk of the variable power lens group used in the conventional example is minimized. This makes it easy to set the lateral magnification β5 of the final lens group to be small.

  As a result, it is possible to obtain an intermediate focus movement amount Δsk that is sufficiently small with respect to the permissible depth, and to have a configuration in which the degree of freedom of design of the variable power lens unit is greater than that of the conventional example. A zoom lens for a liquid crystal projector projection lens having bright FNO and good imaging performance can be provided. In addition, by setting the stop in the second lens group, the third lens group, or the fourth lens group instead of the fifth lens group of the final lens group, the telecentricity of the zoom lens can be ensured.

  Next, an embodiment in which the zoom lens of the present invention is applied to an image projection apparatus (projector) will be described with reference to FIG. In this figure, the zoom lens of the present invention is applied to a three-plate type color liquid crystal projector, and image information of a plurality of color lights based on a plurality of liquid crystal display elements is synthesized through a color synthesizing means, and is projected onto the screen surface by a projection lens. 1 shows an image projection apparatus that performs enlarged projection.

  In FIG. 7, the color liquid crystal projector 100 has three panels of R, G, and B. Further, a prism 200 is provided as a color synthesizing means for each color light from R, G, B. Then, they are combined into one optical path and projected onto the screen 400 using the projection lens 300 composed of the zoom lens described above. Thus, by applying the zoom lenses of Embodiments 1 to 3 to a projector or the like, an image projection apparatus having high optical performance can be realized.

Next, numerical example data in each example of the present invention is shown below. In the numerical examples, i indicates the order of the surfaces from the object side (enlarged conjugate side), ri is the radius of curvature of the lens surface, di is the lens thickness and air spacing between the i-th surface and the i + 1-th surface, ndi, νdi Represents the refractive index and Abbe number for the d-line, respectively. The four surfaces on the image side correspond to glass blocks. The final surface corresponds to the image display element surface. The back focus BF is an air equivalent value from the last lens surface to the image display element surface. K, A, B, C, D, and E are aspheric coefficients. E-0X means 10- ^X .

  The aspherical shape is defined by the following expression when the displacement in the optical axis direction at the position of the height h from the optical axis is x with respect to the surface vertex. Here, R is a radius of curvature. The relationship between the numerical values of the above-described embodiments and conditional expressions, the refractive power of each lens group, and the intermediate focus movement amount Δsk is shown.

x = (h ² / R) / [1+ {1− (1 + k) (h / R) ² } ^1/2 ] + Ah ⁴ + Bh ⁶ + Ch ⁸
+ Dh ¹⁰ + Eh ^{12 The} wide angle indicates the wide angle end, the intermediate indicates the intermediate zoom position, and the telephoto indicates the telephoto end.

[Numerical Example 1]

(A) Lens configuration

Wide angle Medium telephoto
f (Focal distance) 21.60 23.77 26.13
F (Aperture ratio) 2.0 2.2 2.4
Half angle of view (degrees) 29.4 27.1 25.0
Total lens length 148.6
BF 44.7
Zoom ratio 1.21

r1 = 33.09 d1 = 2.00 n1 = 1.717 ν1 = 47.9
r2 = 18.54 d2 = 8.67
r3 * = 59.92 d3 = 2.19 n2 = 1.530 ν2 = 55.8
r4 * = 26.73 d4 = 9.07
r5 = -42.24 d5 = 2.00 n3 = 1.487 ν3 = 70.2
r6 = 97.64 d6 = 20.98
r7 = 96.11 d7 = 7.00 n4 = 1.571 ν4 = 53.0
r8 = -55.90 d8 = variable
r9 = 43.90 d9 = 5.15 n5 = 1.567 ν5 = 42.8
r10 = -160.95 d10 = 3.02
r11 = -84.09 d11 = 1.00 n6 = 1.755 ν6 = 27.5
r12 = -726.25 d12 = 43.24
r13 = 76.33 d13 = 2.89 n7 = 1.487 ν7 = 70.2
r14 = -32.19 d14 = 0.80 n8 = 1.806 ν8 = 33.3
r15 = -287.56 d15 = variable
r16 = -37.76 d16 = 0.80 n9 = 1.744 ν9 = 44.8
r17 = 73.11 d17 = 0.88
r18 = 168.98 d18 = 2.07 n10 = 1.516 ν10 = 64.1
r19 = -51.34 d19 = variable
r20 = -213.74 d20 = 1.00 n11 = 1.806 ν11 = 33.3
r21 = 51.78 d21 = 5.28 n12 = 1.487 ν12 = 70.2
r22 = -47.36 d22 = 0.50
r23 = 103.39 d23 = 4.12 n13 = 1.487 ν13 = 70.2
r24 = -84.69 d24 = variable
r25 = 64.21 d25 = 5.87 n14 = 1.581 ν14 = 40.7
r26 = -72.80 d26 = 1.50
r27 = ∞ d27 = 34.60 n15 = 1.516 ν15 = 64.1
r28 = ∞ d28 = 4.00
r29 = ∞ d29 = 21.00 n16 = 1.805 ν16 = 25.4
r30 = ∞ d30 = 4.70
r31 = ∞

Group spacing Wide angle Medium telephoto
d8 8.99 4.75 0.51
d15 1.61 5.86 10.09
d19 8.98 4.73 0.50
d24 0.50 4.75 8.98


(B) Aspheric coefficient
KABCDE
r3 0 6.68E-05 -2.80E-07 8.54E-10 -1.60E-12 1.51E-15
r4 0 5.88E-05 -2.94E-07 5.50E-10 -5.49E-13 -3.83E-16


(C) Various data
Allowable depth 0.0224
Δsk 0.0000163
φ1 / φw -0.20
φ2 / φw 0.19
φ3 / φw -0.35
φ4 / φw 0.25
φ5 / φw 0.36

[Numerical Example 2]
(A) Lens configuration

Wide angle Medium telephoto
f (Focal distance) 21.60 23.80 26.47
F (Aperture ratio) 2.1 2.2 2.4
Half angle of view (degrees) 29.4 27.1 24.7
Total lens length 135.5
BF 44.7
Zoom ratio 1.23

r1 = 36.79 d1 = 3.77 n1 = 1.638 ν1 = 57.1
r2 = 18.82 d2 = 7.53
r3 * = 100.00 d3 = 2.01 n2 = 1.530 ν2 = 55.8
r4 * = 45.96 d4 = 8.15
r5 = -281.79 d5 = 2.00 n3 = 1.620 ν3 = 60.3
r6 = 56.98 d6 = 23.11
r7 = 82.05 d7 = 3.73 n4 = 1.755 ν4 = 27.6
r8 = -116.18 d8 = variable
r9 = 46.75 d9 = 4.11 n5 = 1.506 ν5 = 60.5
r10 = -86.23 d10 = 5.99
r11 = 313.16 d11 = 2.80 n6 = 1.502 ν6 = 68.9
r12 = -36.58 d12 = 1.00 n7 = 1.752 ν7 = 31.0
r13 = 109.51 d13 = variable
r14 = -55.34 d14 = 1.00 n8 = 1.747 ν8 = 37.8
r15 = 87.42 d15 = 1.14
r16 = -156.99 d16 = 2.10 n9 = 1.499 ν9 = 69.2
r17 = -40.34 d17 = variable
r18 = 122.08 d18 = 1.50 n10 = 1.749 ν10 = 35.2
r19 = 49.71 d19 = 4.93 n11 = 1.694 ν11 = 49.4
r20 = -72.81 d20 = 3.53
r21 = 56.62 d21 = 1.50 n12 = 1.689 ν12 = 30.9
r22 = 41.28 d22 = variable
r23 = 100.30 d23 = 1.89 n13 = 1.495 ν13 = 69.6
r24 = -478.74 d24 = 0.50
r25 = 43.70 d25 = 3.26 n14 = 1.487 ν14 = 70.4
r26 = 621.70 d26 = 1.50
r27 = ∞ d27 = 34.60 n15 = 1.516 ν15 = 64.1
r28 = ∞ d28 = 4.00
r29 = ∞ d29 = 21.00 n16 = 1.805 ν16 = 25.4
r30 = ∞ d30 = 4.70
r31 = ∞

Group spacing Wide angle Medium telephoto
d8 28.24 22.83 16.93
d13 2.00 7.41 13.31
d17 17.76 12.35 6.45
d22 1.92 7.33 13.22


(B) Aspheric coefficient
KABCDE
r3 0 6.27E-05 -2.71E-07 1.39E-09 -3.99E-12 4.80E-15
r4 0 5.88E-05 -2.93E-07 1.55E-09 -5.00E-12 6.02E-15


(C) Various data
Allowable depth 0.0224
Δsk 0.0004806
φ1 / φw -0.09
φ2 / φw 0.14
φ3 / φw -0.27
φ4 / φw 0.23
φ5 / φw 0.35

[Numerical Example 3]
(A) Lens configuration

Wide angle Medium telephoto
f (Focal distance) 21.60 23.79 26.79
F (Aperture ratio) 2.0 2.2 2.5
Half angle of view (degrees) 29.4 27.1 24.4
Total lens length 135.7
BF 44.7
Zoom ratio 1.24

r1 = 34.63 d1 = 2.00 n1 = 1.744 ν1 = 44.9
r2 = 18.98 d2 = 8.95
r3 * = 99.25 d3 = 2.36 n2 = 1.527 ν2 = 66.5
r4 * = 32.47 d4 = 7.93
r5 = -52.58 d5 = 1.50 n3 = 1.531 ν3 = 66.2
r6 = 186.85 d6 = 18.02
r7 = 96.05 d7 = 5.86 n4 = 1.631 ν4 = 35.3
r8 = -67.93 d8 = variable
r9 = 43.34 d9 = 5.02 n5 = 1.540 ν5 = 49.4
r10 = -113.07 d10 = 3.30
r11 = -79.43 d11 = 1.00 n6 = 1.755 ν6 = 27.6
r12 = -2251.25 d12 = 37.23
r13 = 103.68 d13 = 2.73 n7 = 1.487 ν7 = 70.4
r14 = -33.23 d14 = 1.22 n8 = 1.754 ν8 = 28.8
r15 = -121.53 d15 = variable
r16 = -45.14 d16 = 0.80 n9 = 1.744 ν9 = 44.9
r17 = 81.75 d17 = 1.40
r18 = -214.73 d18 = 1.50 n10 = 1.498 ν10 = 64.4
r19 = -53.91 d19 = variable
r20 = 5821.88 d20 = 1.00 n11 = 1.755 ν11 = 27.6
r21 = 56.03 d21 = 4.66 n12 = 1.487 ν12 = 70.4
r22 = -53.35 d22 = 0.5
r23 = 97.89 d23 = 3.34 n13 = 1.487 ν13 = 70.4
r24 = -131.60 d24 = variable
r25 = 66.14 d25 = 4.54 n14 = 1.669 ν14 = 37.4
r26 = -108.89 d26 = 1.50
r27 = ∞ d27 = 34.60 n15 = 1.516 ν15 = 64.1
r28 = ∞ d28 = 4.00
r29 = ∞ d29 = 21.00 n16 = 1.805 ν16 = 25.4
r30 = ∞ d30 = 4.70
r31 = ∞

Group spacing Wide angle Medium telephoto
d8 10.33 6.59 2.00
d15 1.20 4.94 9.53
d19 8.83 5.09 0.50
d24 0.50 4.24 8.83


(B) Aspheric coefficient
KABCDE
r3 0 6.63E-05 -2.59E-07 8.25E-10 -1.62E-12 1.66E-15
r4 0 5.92E-05 -2.60E-07 5.42E-10 -6.26E-13 -1.01E-16

(C) Various data
Allowable depth 0.0224
Δsk 0.0001461
φ1 / φw -0.22
φ2 / φw 0.22
φ3 / φw -0.38
φ4 / φw 0.28
φ5 / φw 0.35

B1 1st lens group B2 2nd lens group B3 3rd lens group B4 4th lens group B5 5th lens group

Claims (7)

In order from the magnification conjugate side to the reduction conjugate 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 group having a positive refractive power, The fifth lens unit has a positive refractive power, and the second lens unit and the fourth lens unit move to the magnification conjugate side along the same locus during zooming from the wide-angle end to the telephoto end. In the zoom lens in which the group, the third lens group, and the fifth lens group are stationary, the combined focal length of the second lens group, the third lens group, and the fourth lens group at the wide-angle end is f2 to 4w, When the lateral magnification of the fifth lens group at the wide angle end is β5w and the focal length of the entire system at the wide angle end is fw,
6.0 ≦ f2-4w / fw <10.0
0.05 <β5w <0.30
A zoom lens satisfying the following conditional expression: When the optical total length is L, and the distance from the lens surface closest to the magnification conjugate side of the first lens group to the object side principal point of the first lens group is dL,
0.5 <(dL-L) / L <2.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   The zoom lens according to claim 1, wherein the first lens group includes at least one negative lens and at least one positive lens in order from the magnification conjugate side to the reduction conjugate side. The first lens group includes three negative lenses and one positive lens in order from the magnification conjugate side to the reduction conjugate side. The distance between the most negative lens and the positive lens is 1d, and the total optical length is L. and when,
0.1 <1d / L <0.4
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   5. The zoom lens according to claim 1, wherein the second lens group, the third lens group, or the fourth lens group has an aperture stop. 6.   6. The zoom lens according to claim 1, wherein the pupil position on the reduction conjugate side is located at infinity.   7. An image projection comprising: the zoom lens according to claim 1; and an image display element that forms an original image, and the original image formed by the image display element is projected by the zoom lens. apparatus.