JP5407573B2 - Zoom lens and projector apparatus using the same - Google Patents

Description

Invention relates to a projector apparatus using mainly a DMD's Murenzu and it enlarges and projects a screen other images from the light valve for forming an image by changing the reflecting direction of light such as.

  In recent years, DMD (digital micromirror device) displays images by arranging microscopic micromirrors (mirror elements) on a plane corresponding to pixels and mechanically controlling the angle of each mirror surface using micromachine technology. ) Has been put to practical use, and is characterized by a faster response speed and a brighter image than a liquid crystal panel that has been widely used in this field. It is rapidly spreading because it is suitable for realizing.

  When a DMD is used as a light valve in a projector device, a DMD-specific restriction occurs for a projection lens that is used simultaneously. The first restriction relates to the F value of the projection lens, which is considered to be the largest restriction in developing a small projector device. Currently, in the DMD, when the image is generated, the turning angle to represent ON and OFF of the micromirror is ± 12 °, which enables effective reflected light (effective light) and invalid reflected light (ineffective light). ). Therefore, in a projector apparatus using a DMD as a light valve, it is necessary to capture effective light and not to catch invalid light. From this condition, the F value of the projection lens can be derived, that is, F = 2. 4 Actually, there is a demand for capturing a light amount as much as possible, and therefore, a smaller F value is often required in consideration of a decrease in contrast in a range where there is no actual harm. In addition, since such a condition is established under the condition that the position of the pupil on the light valve side of the projection lens is constant, if the pupil position of the zoom lens or the like moves, the amount of light Since loss or the like occurs, it is generally necessary to consider such as optimizing the pupil position at the wide-angle end where brightness tends to be a problem.

  The second restriction relates to the arrangement with the light source system. Since the image circle of the projection lens is desired to be as small as possible for miniaturization, the arrangement of the light source system for inputting the projection light beam to the DMD is limited. In order to input effective light from the DMD to the projection lens, the light source system is installed in substantially the same direction (adjacent) as the projection lens. In addition, the projection lens and the light source system are used between the light valve side lens of the projection lens and the light valve (in general, the back focus), and the projection lens has a large back. In addition to providing a focus, it is necessary to design a small lens system on the light valve side in order to secure a light guide space from the light source. From the standpoint of optical design of the projection lens, this is a constraint that the pupil position on the light valve side is located near the rear of the projection lens. On the other hand, in order to improve the performance of the projection lens, it is necessary to combine a large number of lenses, and if a large number of lenses are arranged, the total length of the projection lens needs to be a certain length. If the total length of the lens is increased, the lens having the entrance pupil position on the rear side becomes a problem contrary to the size reduction in which the front lens diameter is naturally increased.

In this way, although there are major restrictions on development, a projector device that employs DMD as a light valve is advantageous over other methods in terms of miniaturization, and is now convenient for presentations. Portable portable compact projectors have become widespread, centering on new data projectors. In addition, in order to make the device itself compact, it is natural that there is a strong demand for miniaturization of the projection lens used, and on the other hand, there is also a demand for multi-function, and correction of various aberrations. In addition to satisfying the specifications of the DMD used as a result of the image quality performance as a result of the above, not only zooming is possible in terms of convenience, but the center of the DMD and the optical axis of the projection lens are In order to adopt a shifted so-called shift configuration, a lens with a large image circle is required, and a lens with a large angle of view at the wide-angle end and a lens with a large zoom ratio have been required. . In the projection lens developed with such specifications, the aperture of the front lens group tends to be larger than desired, which greatly affects the thickness of the projector device. However, it is important to reduce the thickness of a projector device that is assumed to be portable, and it is the most important factor for projector devices that are often used with laptop personal computers. It can also be said.
As a means for solving this problem, there is an example of a compact design method for a projection lens. (Patent Document 1)

JP 2004-271668 A

  In the technique described in the above-mentioned technical document 1, when the 0.7-inch DMD is used, the effective diameter of the front lens is 39 mm to 42 mm, and at least the thickness of the projector device cannot be 50 mm or less. When this thickness is actually carried with a notebook type personal computer or the like, the thickness is still unsatisfactory.

  In view of the above-described circumstances, the present invention is suitable for the characteristics of a light valve that forms an image by changing the reflection direction of light, such as DMD, and enlarges and projects an image from the light valve on a screen or other wall surface. A compact zoom lens with high imaging performance and a small lens aperture in applications, is compact and bright, and has a high image quality that can project a large screen even in a limited space such as a small conference room. An object of the present invention is to provide a projector device.

According to the first aspect of the present invention, in order from the magnification side, the first lens group having a negative refractive power as a whole, the second lens group having a positive refractive power as a whole, and the third lens having a positive refractive power as a whole The first lens group includes, in order from the magnifying side, a meniscus lens having a negative refractive power convex to the magnifying side, a negative lens, a lens having a positive refracting power, a negative lens, and a positive lens. The second lens group includes five lenses: a positive lens in order from the magnification side, and a concave meniscus negative lens, a positive lens, a negative lens, and a positive lens on the magnification side. The third lens group is a zoom lens capable of zooming configured by arranging one positive lens, and the third lens group is fixed during zooming operation, One lens unit extends from the wide-angle end to the middle range from the enlargement side to the reduction side The second lens group moves on the optical axis from the reduction side to the enlargement side from the wide-angle end to the telephoto end. Thus, the entire lens system is zoomed, and the following conditional expression (1) relates to the distance on the optical axis from the magnifying side surface of the lens disposed closest to the magnifying side in the first lens group at the wide-angle end to the focal position. ), The following conditional expression (2) is satisfied regarding the positional relationship between the second lens group and the third lens group at the wide-angle end, and the magnification at the wide-angle end of the second lens group is described below. Conditional expression (3) is satisfied, the following conditional expression (4) is satisfied with respect to the power of the first lens group, and the following conditional expression (5) is satisfied with respect to the magnification at the telephoto end of the second lens group. Of the second lens group Characterized in that it satisfies the following conditional expression (6) with respect to lens power arranged from the larger side to the fourth sheet.
(1) 7.0 <TL / _fw <10.0
(2) 1.8 < _dIIw / _fw <2.5
(3) −1.0 <m _{II w} <−0.5
_{(4) -1.0 <f w /} f I <-0.5
(5) 1.4 <m _{II T} / m _{II w} <2.8
_{(6) -0.7 <f w /} f 9 <-0.6
However,
TL: Distance on the optical axis from the magnifying side surface of the lens arranged closest to the magnifying side in the first lens unit at the wide angle end to the in-focus position (according to the magnifying side object distance of 1700 mm from the magnifying side most of the first lens unit) Out of focus)
f _w : Combined focal length of the entire lens system at the wide-angle end (focused state on the enlargement side object distance of 1700 mm from the most enlargement side surface of the first lens group)
d _{II w} : Air distance between the second lens group and the third lens group at the wide angle end f _I : Composite focal length of the first lens group at the wide angle end (magnification side object distance from the most magnifying side of the first lens group) Focused on 1700mm)
m _{II w} : magnification of the second lens group at the wide angle end m _{II T} : magnification of the second lens group at the telephoto end f ₉ : focal length of the lens disposed on the fourth lens from the magnification side of the second lens group (1) is a condition for the distance on the optical axis from the magnifying side surface of the lens arranged closest to the magnifying side in the first lens group at the wide angle end to the in-focus position, and is a condition for miniaturization and diameter reduction. If the upper limit is exceeded, the distance from the magnifying side of the lens arranged closest to the magnifying side in the first lens group at the wide-angle end to the in-focus position becomes large, and the lens becomes a large aperture, which impairs the reduction in size and size. If the lower limit is exceeded, it becomes difficult to balance various aberrations.
Conditional expression (2) is an interval condition at the wide-angle end of the second lens group and the third lens group. As described above, it is necessary to secure this space because of the space of the illumination system of the light valve. If the upper limit is exceeded, the space for the illumination system can be secured, but the lens becomes larger, and if the upper limit is exceeded, the space for the illumination system is insufficient and design becomes difficult.
Conditional expression (3) corresponds to the magnification of the second lens group, and is a condition for reducing the size of the entire lens system over the zooming range. If the lower limit is exceeded, the total length at the reduction magnification becomes longer, and if the upper limit is exceeded, enlargement occurs. The total length at the magnification becomes longer.
Conditional expression (4) is a condition regarding the power of the first lens group. The first lens group has a strong negative power and has a purpose of securing a space for arranging an optical system for illuminating a light valve such as a DMD in an air space portion between the second lens group and the third lens group. ing. When the upper limit is exceeded, the negative power of the first lens group becomes small, and it becomes difficult to secure the air gap between the second lens group and the third lens group. When the upper limit is exceeded, the negative power increases and the second power increases. The positive power of the lens group must be strengthened, making it difficult to balance various aberrations.
Conditional expression (5) is a conditional expression regarding the magnification at the wide-angle end of the second lens group and the magnification at the telephoto end of the second lens group, and corresponds to the variable magnification of the zoom lens system. If the upper limit is exceeded, a lens system with a large zoom ratio can be obtained, but the amount of movement of the second lens group increases and the size of the second lens group increases, and the fluctuation in performance also increases. However, the zoom ratio itself becomes small, and the small and high zoom lens according to the present invention cannot be obtained.
Conditional expression (6) is a condition for correcting the divergent light beam from the first lens group, ensuring a large aperture ratio, and correcting spherical aberration and coma aberration. The second lens group has a strong positive power for guiding the diverging beam bundle exiting the first lens group into a focused state, and various aberrations such as spherical aberration occur. The lenses constituting the second lens group are three lenses, a positive lens, a negative lens, and a positive lens from the magnifying surface side, and various aberrations are corrected as a triplet structure, but the positive power of the second lens group is strong. Therefore, the aberration correction becomes insufficient, so that the aberration correction is made possible by disposing a negative lens on the reduction side of the triplet configuration lens. When the upper limit of conditional expression (6) is exceeded, under spherical aberration increases, and when the lower limit is exceeded, over spherical aberration increases, resulting in significant coma in the periphery, making it difficult to correct aberrations.

The second aspect of the invention satisfies the following conditional expression (7) with respect to the dimension on the optical axis of the first lens group in the first lens group, and satisfies the following conditional expression with respect to the power of the lens arranged closest to the enlargement side. (8) is satisfied, the following conditional expression (9) is satisfied with respect to the shape of the reduction side surface of the lens arranged closest to the magnifying side in the first lens group, and it is used for each lens constituting the first lens group. The following conditional expression (10) is satisfied with respect to the dispersion characteristics of the glass material.
_{(7) 1.4 <L I /} f w <2.3
_{(8) -0.7 <f w /} f 1 <-0.2
_{(9) 0.8 <f w /} r 2 <1.5
(10) 16 <(V ₁ + V ₂ + V ₄ ) / 3- (V ₃ + V ₅ ) / 2
However,
L _I : Distance f ₁ on the optical axis between the enlargement side surface of the lens arranged closest to the enlargement side in the first lens group and the reduction side surface of the lens arranged closest to the reduction side in the first lens group f ₁ : first lens group The focal length r _{2 of} the lens arranged closest to the magnification side: radius of curvature V ₁ of the reduction side of the lens arranged closest to the magnification side in the first lens group V ₁ : negative arranged closest to the magnification side in the first lens group Lens Abbe number V ₂ : Abbe number of the negative lens disposed on the second lens from the magnification side in the first lens group V ₃ : Abbe number of the positive lens disposed on the third lens from the magnification side in the first lens group V ₄ : Abbe number of the negative lens arranged in the fourth lens from the magnification side in the first lens group V ₅ : Abbe number of the positive lens arranged closest to the reduction side in the first lens group Conditional expression ( 7 ) is This is a conditional expression related to the dimensions of the first lens group on the optical axis. It becomes a condition for. In order to increase the length corresponding to the back focus between the second lens group and the third lens group, it is particularly effective to increase the negative power of the lens arranged closest to the enlargement side in the first lens group. However, when the negative power is excessive, it is difficult to correct various aberrations. This can be solved by increasing the distance on the optical axis of the first lens group, or by increasing the number of lenses in order to disperse the negative power of the first lens group. The first lens group has to be long to some extent. If the upper limit of conditional expression ( 7 ) is exceeded, the dimension in the optical axis direction becomes too large to satisfy the specifications, making it difficult to reduce the size, and if the lower limit is exceeded, it is difficult to reduce the aperture.
Conditional expression ( 8 ) is a condition relating to the power of the lens arranged closest to the magnification side of the first lens group, and increases the negative power of the lens arranged closest to the magnification side of the first lens group as described above. This is effective for ensuring the air space between the second lens group and the third lens group at the wide-angle end and reducing the size. However, if the upper limit of conditional expression (8) is exceeded, the negative power of the lens becomes stronger. Chromatic aberration and curvature of field occur, making it difficult to correct the aberration. If the lower limit is exceeded, the negative power of the lens becomes weak, and a portion corresponding to the back focus between the second lens group and the third lens group is made long. Becomes difficult.
Conditional expression (9) is a conditional expression for correcting distortion and coma aberration of the entire lens system. This relates to the shape of the lens on the reduction side of the lens arranged closest to the magnifying side of the first lens group. While giving a strong power, the shape is substantially concentric with the light beam on the magnifying side, and fundamentally generates aberrations. The shape is suppressed. Therefore, when the upper limit is exceeded, spherical aberration and coma aberration are undercorrected, and when the lower limit is exceeded, overcorrection is conversely performed.
Conditional expression (10) is a condition for correcting chromatic aberration in the first lens group. In order to correct the monochromatic aberration, it is necessary that the power of each lens does not become excessive. For that purpose, the Abbe numbers of the positive lens and the negative lens satisfying the conditional expression (10) are necessary. When the lower limit is exceeded, it becomes difficult to correct chromatic aberration.

According to a third aspect of the present invention, the focusing operation is achieved by moving the first lens group in the optical axis direction, and the second lens from the magnifying side is the second lens group constituting the first lens group. Regarding the lens to be arranged, conditional expression (11) is satisfied, and at least one surface of the second lens arranged in the first lens group is aspherical.
(11) −0.5 <f _w / f ₂
However,
f ₂ : Focal length of the second lens arranged from the magnification side in the first lens group As described above, increasing the negative power of the lens arranged closest to the magnification side in the first lens group is a wide angle. The air gap between the second lens group and the third lens group at the end is ensured and effective for miniaturization. However, since it is difficult to correct various aberrations including curvature of field in the spherical shape, the first lens By using an aspherical lens with weak negative power that satisfies the conditional expression (1 1 ) as the second lens from the magnification side of the group, various aberrations including field curvature can be corrected. . Setting a weak negative power that satisfies the conditional expression (1 1 ) can use a plastic material, which is a glass material having a low refractive index, and thus can reduce weight and cost.

According to a fourth aspect of the present invention, the second lens group includes a positive lens in order from the magnifying side, a negative meniscus negative lens on the magnifying side, a positive lens, a negative lens, and a positive lens. The following conditional expression (12) is satisfied with respect to the shape on the magnifying side of the lens arranged closest to the magnifying side among the lens groups constituting the two lens groups, and is used for each of the five lenses constituting the second lens group. The following conditional expression (13) is satisfied with respect to the dispersion characteristics of the glass material, and the following conditional expression (14) is satisfied with respect to the dispersion characteristics of the lens disposed on the most reduction side of the second lens group. Features.
_{(12) 0.2 <f w /} r II 1 <0.8
_{(13) 25 <(V 6} + V 8 + V 10) / 3- (V 7 + V 9) / 2
(14) 69 <V ₁₀
However,
r _{II 1} : radius of curvature V ₆ of the magnifying side surface of the lens arranged closest to the magnifying side of the second lens group V ₆ : Abbe number V _{7 of the} positive lens laid out closest to the magnifying side of the second lens group In the second lens group, the Abbe number V _{8 of} the second lens arranged from the magnifying side is V ₈ : The Abbe number V _{9 of the} positive lens arranged from the magnifying side in the second lens group is V ₉ : From the magnifying side in the second lens group Abbe number V _{10 of the} negative lens arranged on the fourth lens: Abbe number of the positive lens arranged closest to the reduction side in the second lens group Conditional expression (12) is arranged on the most enlargement side of the second lens group. It is a conditional expression regarding the shape of the expansion side surface of the positive lens. The lens arranged on the magnifying side in the second lens group needs to be a lens having a strong positive power for guiding the divergent light beam emitted from the first lens group to a converged state. In order to generate chromatic aberration, it is necessary to have a shape that allows aberration correction with the second and subsequent lenses of the second lens group. When the upper limit of conditional expression (12) is exceeded, the surface power increases and under spherical aberration increases, and when the lower limit is exceeded, the surface power decreases and over spherical aberration increases, making correction difficult.
Conditional expression (13) is a condition for correcting chromatic aberration in the second lens group. In order to correct the monochromatic aberration, it is necessary that the power of each lens does not become excessive. For that purpose, it is necessary that the Abbe numbers of the positive lens and the negative lens satisfy the conditional expression (13). When the lower limit is exceeded, it becomes difficult to correct chromatic aberration.
Conditional expression (14) is a condition for correcting the lateral chromatic aberration. Since the second lens group has a strong positive power, it has a great influence on the lateral chromatic aberration. In particular, the influence of the positive lens arranged closest to the reduction side having the strongest positive power in the second lens group is great, and if the lower limit of conditional expression (14) is exceeded, aberration correction becomes difficult.

According to a fifth aspect of the present invention, at least one surface of the lens disposed second from the magnification side of the second lens group has an aspherical shape, and the lens disposed closest to the reduction side of the second lens group. The following conditional expression (15) is satisfied with respect to the shape of the reduction side surface.
_{(15) -0.8 <f w /} r II 10 <-0.2
However,
r _{II 10} : radius of curvature of the reduction side surface of the lens arranged closest to the reduction surface side of the second lens group As described above, the second lens group is a state in which the divergent light beam emitted from the first lens group is focused. It has a strong positive power to lead to the occurrence of various aberrations such as spherical aberration. The lenses constituting the second lens group are three lenses, a positive lens, a negative lens, and a positive lens from the magnifying surface side, and various aberrations are corrected as a triplet structure, but the positive power of the second lens group is strong. Therefore, the aberration correction becomes insufficient, so that the aberration correction is made possible by disposing a negative lens on the reduction side of the triplet configuration lens. However, since the spherical shape may cause insufficient aberration correction, at least one surface of the second lens arranged from the magnifying side of the second lens group is made aspherical so that a large aperture ratio of the entire lens system is obtained. This makes it possible to reduce the diameter of the entire lens system and correct spherical aberration and the like.
Conditional expression (15) is a conditional expression for finely correcting spherical aberration and coma aberration in the entire lens system. From the enlarged side surface of the second lens group, the remaining four spherical aberrations and coma aberration are corrected by the four lenses. When the upper limit is exceeded, the correction is insufficient, and when the lower limit is exceeded, the correction is excessive.

  The invention described in claim 6 provides a thin projector device that can be miniaturized as a whole by mounting the compact zoom lens according to the present invention in the projector device, and is convenient for carrying. I can do it.

  According to the present invention, a compact zoom lens with high imaging performance suitable for the characteristics of a light valve such as DMD can be realized, and a compact, bright and high-quality projector can be provided.

1 is a lens configuration diagram of a first embodiment of a compact zoom lens according to the present invention. Various aberration diagrams of the lens of the first example Lens configuration diagram of a second embodiment of a compact zoom lens according to the present invention Various aberration diagrams of the lens of the second example Lens configuration diagram of a third embodiment of a compact zoom lens according to the present invention Various aberration diagrams of the lens of the third example

The zoom lens of the present invention includes, in order from the magnification side, a first lens group having a negative refractive power as a whole, a second lens group having a positive refractive power as a whole, and a third lens group having a positive refractive power as a whole. The first lens group includes, in order from the magnifying side, a meniscus lens convex on the magnifying side and a negative refractive power, a negative lens, a lens having a positive refracting power, a negative lens, and a positive lens The second lens group includes a positive lens in order from the magnifying side, and a concave meniscus negative lens, a positive lens, a negative lens, and a positive lens on the magnifying side. The third lens group is a zoom lens capable of zooming configured by arranging one positive lens, and the third lens group is fixed during zooming operation, The lens group is reduced from the magnification side from the wide-angle end to the middle range The second lens group moves on the optical axis from the wide-angle end to the telephoto end from the reduction side to the enlargement side direction. Thus, the entire lens system is zoomed, and the following conditional expression (1) relates to the distance on the optical axis from the magnifying side surface of the lens disposed closest to the magnifying side in the first lens group at the wide-angle end to the focal position. ), The following conditional expression (2) is satisfied regarding the positional relationship between the second lens group and the third lens group at the wide-angle end, and the magnification at the wide-angle end of the second lens group is described below. Conditional expression (3) is satisfied, the following conditional expression (4) is satisfied with respect to the power of the first lens group, and the following conditional expression (5) is satisfied with respect to the magnification at the telephoto end of the second lens group. And the second lens group Characterized in that it satisfies the following conditional expression (6) with respect to a power of the lens disposed from the enlargement side to the fourth sheet.
(1) 7.0 <TL / _fw <10.0
(2) 1.8 < _dIIw / _fw <2.5
(3) −1.0 <m _{II w} <−0.5
_{(4) -1.0 <f w /} f I <-0.5
(5) 1.4 <m _{II T} / m _{II w} <2.8
_{(6) -0.7 <f w /} f 9 <-0.6
However,
TL: Distance on the optical axis from the magnifying side surface of the lens arranged closest to the magnifying side in the first lens unit at the wide angle end to the in-focus position (according to the magnifying side object distance of 1700 mm from the magnifying side most of the first lens unit) Out of focus)
f _w : Combined focal length of the entire lens system at the wide-angle end (focused state on the enlargement side object distance of 1700 mm from the most enlargement side surface of the first lens group)
d _{II w} : Air distance between the second lens group and the third lens group at the wide angle end f _I : Composite focal length of the first lens group at the wide angle end (magnification side object distance from the most magnifying side of the first lens group) Focused on 1700mm)
m _{II w} : magnification of the second lens group at the wide angle end m _{II T} : magnification of the second lens group at the telephoto end f ₉ : focal length of the lens disposed on the fourth lens from the magnification side of the second lens group (1) is a condition for the distance on the optical axis from the magnifying side surface of the lens arranged closest to the magnifying side in the first lens group at the wide angle end to the in-focus position, and is a condition for miniaturization and diameter reduction. If the upper limit is exceeded, the distance from the magnifying side of the lens arranged closest to the magnifying side in the first lens group at the wide-angle end to the in-focus position becomes large, and the lens becomes a large aperture, which impairs the reduction in size and size. If the lower limit is exceeded, it becomes difficult to balance various aberrations.
Conditional expression (2) is an interval condition at the wide-angle end of the second lens group and the third lens group. As described above, it is necessary to secure this space because of the space of the illumination system of the light valve. If the upper limit is exceeded, the space for the illumination system can be secured, but the lens becomes larger, and if the upper limit is exceeded, the space for the illumination system is insufficient and design becomes difficult.
Conditional expression (3) corresponds to the magnification of the second lens group, and is a condition for reducing the size of the entire lens system over the zooming range. If the lower limit is exceeded, the total length at the reduction magnification becomes longer, and if the upper limit is exceeded, enlargement occurs. The total length at the magnification becomes longer.
Conditional expression (4) is a condition regarding the power of the first lens group. The first lens group has a strong negative power and has a purpose of securing a space for arranging an optical system for illuminating a light valve such as a DMD in an air space portion between the second lens group and the third lens group. ing. When the upper limit is exceeded, the negative power of the first lens group becomes small, and it becomes difficult to secure the air gap between the second lens group and the third lens group. When the upper limit is exceeded, the negative power increases and the second power increases. The positive power of the lens group must be strengthened, making it difficult to balance various aberrations.
Conditional expression (5) is a conditional expression regarding the magnification at the wide-angle end of the second lens group and the magnification at the telephoto end of the second lens group, and corresponds to the variable magnification of the zoom lens system. If the upper limit is exceeded, a lens system with a large zoom ratio can be obtained, but the amount of movement of the second lens group increases and the size of the second lens group increases, and the fluctuation in performance also increases. However, the zoom ratio itself becomes small, and the small and high zoom lens according to the present invention cannot be obtained.
Conditional expression (6) is a condition for correcting the divergent light beam from the first lens group, ensuring a large aperture ratio, and correcting spherical aberration and coma aberration. The second lens group has a strong positive power for guiding the diverging beam bundle exiting the first lens group into a focused state, and various aberrations such as spherical aberration occur. The lenses constituting the second lens group are three lenses, a positive lens, a negative lens, and a positive lens from the magnifying surface side, and various aberrations are corrected as a triplet structure, but the positive power of the second lens group is strong. Therefore, the aberration correction becomes insufficient, so that the aberration correction is made possible by disposing a negative lens on the reduction side of the triplet configuration lens. When the upper limit of conditional expression (6) is exceeded, under spherical aberration increases, and when the lower limit is exceeded, over spherical aberration increases, resulting in significant coma in the periphery, making it difficult to correct aberrations.

In the first lens group, the following conditional expression (7) is satisfied with respect to the dimension on the optical axis of the first lens group, and the following conditional expression (8) is satisfied with respect to the power of the lens arranged on the most magnified side. The following conditional expression (9) is satisfied with respect to the shape of the reduction side surface of the lens arranged closest to the magnifying side in the first lens group, and the dispersion characteristics of the glass material used for each lens constituting the first lens group: It is preferable that the following conditional expression (10) is satisfied.
_{(7) 1.4 <L I /} f w <2.3
_{(8) -0.7 <f w /} f 1 <-0.2
_{(9) 0.8 <f w /} r 2 <1.5
(10) 16 <(V ₁ + V ₂ + V ₄ ) / 3- (V ₃ + V ₅ ) / 2
However,
L _I : Distance f ₁ on the optical axis between the enlargement side surface of the lens arranged closest to the enlargement side in the first lens group and the reduction side surface of the lens arranged closest to the reduction side in the first lens group f ₁ : first lens group The focal length r _{2 of} the lens arranged closest to the magnification side: radius of curvature V ₁ of the reduction side of the lens arranged closest to the magnification side in the first lens group V ₁ : negative arranged closest to the magnification side in the first lens group Lens Abbe number V ₂ : Abbe number of the negative lens disposed on the second lens from the magnification side in the first lens group V ₃ : Abbe number of the positive lens disposed on the third lens from the magnification side in the first lens group V ₄ : Abbe number of the negative lens arranged in the fourth lens from the magnification side in the first lens group V ₅ : Abbe number of the positive lens arranged closest to the reduction side in the first lens group Conditional expression ( 7 ) is This is a conditional expression related to the dimensions of the first lens group on the optical axis. It becomes a condition for.
In order to increase the length corresponding to the back focus between the second lens group and the third lens group, it is particularly effective to increase the negative power of the lens arranged closest to the enlargement side in the first lens group. However, when the negative power is excessive, it is difficult to correct various aberrations. This can be solved by increasing the distance on the optical axis of the first lens group, or by increasing the number of lenses in order to disperse the negative power of the first lens group. The first lens group has to be long to some extent. If the upper limit of conditional expression ( 7 ) is exceeded, the dimension in the optical axis direction becomes too large to satisfy the specifications, making it difficult to reduce the size, and if the lower limit is exceeded, it is difficult to reduce the aperture.
Conditional expression ( 8 ) is a condition relating to the power of the lens arranged closest to the magnification side of the first lens group, and increases the negative power of the lens arranged closest to the magnification side of the first lens group as described above. This is effective for ensuring the air space between the second lens group and the third lens group at the wide-angle end and reducing the size. However, if the upper limit of conditional expression (8) is exceeded, the negative power of the lens becomes stronger. Chromatic aberration and curvature of field occur, making it difficult to correct the aberration. If the lower limit is exceeded, the negative power of the lens becomes weak, and a portion corresponding to the back focus between the second lens group and the third lens group is made long. Becomes difficult.
Conditional expression (9) is a conditional expression for correcting distortion and coma aberration of the entire lens system.
This relates to the shape of the lens on the reduction side of the lens arranged closest to the magnifying side of the first lens group. While giving a strong power, the shape is substantially concentric with the light beam on the magnifying side, and fundamentally generates aberrations. The shape is suppressed. Therefore, when the upper limit is exceeded, spherical aberration and coma aberration are undercorrected, and when the lower limit is exceeded, overcorrection is conversely performed.
Conditional expression (10) is a condition for correcting chromatic aberration in the first lens group. In order to correct the monochromatic aberration, it is necessary that the power of each lens does not become excessive. For that purpose, the Abbe numbers of the positive lens and the negative lens satisfying the conditional expression (10) are necessary. When the lower limit is exceeded, it becomes difficult to correct chromatic aberration.

The focusing operation is achieved by moving the first lens group in the direction of the optical axis, and a conditional expression regarding the second lens from the magnifying side in the first lens group constituting the first lens group. (11) is satisfied, and it is preferable that at least one surface of the second lens disposed in the first lens group has an aspherical shape.
(11) −0.5 <f _w / f ₂
However,
f ₂ : Focal length of the second lens arranged from the magnification side in the first lens group As described above, increasing the negative power of the lens arranged closest to the magnification side in the first lens group is a wide angle. The air gap between the second lens group and the third lens group at the end is ensured and effective for miniaturization. However, since it is difficult to correct various aberrations including curvature of field in the spherical shape, the first lens By using an aspherical lens with weak negative power that satisfies the conditional expression (1 1 ) as the second lens from the magnification side of the group, various aberrations including field curvature can be corrected. . Setting a weak negative power that satisfies the conditional expression (1 1 ) can use a plastic material, which is a glass material having a low refractive index, and thus can reduce weight and cost.

The second lens group includes a positive lens in order from the magnifying side, a negative meniscus negative lens on the magnifying side, a positive lens, a negative lens, and a positive lens, and constitutes the second lens group. The following conditional expression (12) is satisfied with respect to the shape on the magnifying side of the lens arranged on the most magnifying side, and the dispersion characteristics of the glass material used for each of the five lenses constituting the second lens group are as follows. It is preferable that the conditional expression (13) is satisfied, and the following conditional expression (14) is satisfied with respect to the dispersion characteristics of the lens disposed on the most reduction side of the second lens group.
_{(12) 0.2 <f w /} r II 1 <0.8
_{(13) 25 <(V 6} + V 8 + V 10) / 3- (V 7 + V 9) / 2
(14) 69 <V ₁₀
However,
r _{II 1} : radius of curvature V ₆ of the magnifying side surface of the lens arranged closest to the magnifying side of the second lens group V ₆ : Abbe number V _{7 of the} positive lens laid out closest to the magnifying side of the second lens group In the second lens group, the Abbe number V _{8 of} the second lens arranged from the magnifying side is V ₈ : The Abbe number V _{9 of the} positive lens arranged from the magnifying side in the second lens group is V ₉ : From the magnifying side in the second lens group Abbe number V _{10 of the} negative lens arranged on the fourth lens: Abbe number of the positive lens arranged closest to the reduction side in the second lens group Conditional expression (12) is arranged on the most enlargement side of the second lens group. It is a conditional expression regarding the shape of the expansion side surface of the positive lens. The lens arranged on the magnifying side in the second lens group needs to be a lens having a strong positive power for guiding the divergent light beam emitted from the first lens group to a converged state. In order to generate chromatic aberration, it is necessary to have a shape that allows aberration correction with the second and subsequent lenses of the second lens group.
When the upper limit of conditional expression (12) is exceeded, the surface power increases and under spherical aberration increases, and when the lower limit is exceeded, the surface power decreases and over spherical aberration increases, making correction difficult.
Conditional expression (13) is a condition for correcting chromatic aberration in the second lens group. In order to correct the monochromatic aberration, it is necessary that the power of each lens does not become excessive. For that purpose, it is necessary that the Abbe numbers of the positive lens and the negative lens satisfy the conditional expression (13). When the lower limit is exceeded, it becomes difficult to correct chromatic aberration.
Conditional expression (14) is a condition for correcting the lateral chromatic aberration. Since the second lens group has a strong positive power, it has a great influence on the lateral chromatic aberration. In particular, the influence of the positive lens arranged closest to the reduction side having the strongest positive power in the second lens group is great, and if the lower limit of conditional expression (14) is exceeded, aberration correction becomes difficult.

At least one surface of the second lens arranged from the magnification side of the second lens group has an aspherical shape, and the shape of the surface on the reduction side of the lens arranged closest to the reduction side of the second lens group is described below. It is preferable that conditional expression (15) is satisfied.
_{(15) -0.8 <f w /} r II 10 <-0.2
However,
r _{II 10} : radius of curvature of the reduction side surface of the lens arranged closest to the reduction surface side of the second lens group As described above, the second lens group is a state in which the divergent light beam emitted from the first lens group is focused. It has a strong positive power to lead to the occurrence of various aberrations such as spherical aberration. The lenses constituting the second lens group are three lenses, a positive lens, a negative lens, and a positive lens from the magnifying surface side, and various aberrations are corrected as a triplet structure, but the positive power of the second lens group is strong. Therefore, the aberration correction becomes insufficient, so that the aberration correction is made possible by disposing a negative lens on the reduction side of the triplet configuration lens. However, since the spherical shape may cause insufficient aberration correction, at least one surface of the second lens arranged from the magnifying side of the second lens group is made aspherical so that a large aperture ratio of the entire lens system is obtained. This makes it possible to reduce the diameter of the entire lens system and correct spherical aberration and the like.
Conditional expression (15) is a conditional expression for finely correcting spherical aberration and coma aberration in the entire lens system. From the enlarged side surface of the second lens group, the remaining four spherical aberrations and coma aberration are corrected by the four lenses. When the upper limit is exceeded, the correction is insufficient, and when the lower limit is exceeded, the correction is excessive.

  Thus, by mounting the compact zoom lens according to the present invention on the projector device, the entire device can be reduced in size, and a thin projector device that is convenient for carrying can be provided.

Hereinafter, the present invention will be described with respect to specific numerical examples. In the compact zoom lenses of the following first to third embodiments, in order from the magnification side, a first lens group LG1 having a negative refractive power as a whole, a second lens group LG2 having a negative refractive power as a whole, and The first lens group LG1 is composed of a third lens group LG3 having a positive refractive power as a whole. The first lens group LG1 has a negative meniscus lens having a negative refractive power convex to the enlargement side in order from the enlargement side (lens name L11, Enlarged side surface 101, reduced side surface 102) (hereinafter negative lens), negative lens (lens name L12, enlarged side surface 103, reduced side surface 104), lens having positive refractive power (lens name L13, enlarged side surface 105, reduced side surface 106) (Hereinafter positive lens), negative lens (lens name L14, enlargement side 107, reduction side 108), and positive lens (lens name L15, enlargement side 108, reduction side 109) The second lens group LG2 is composed of five lenses including three positive lenses and two negative lenses (lens names L21, L22,... In order from the enlargement side). The surface names are 201, 202,... In order from the enlargement side, and the third lens group LG3 includes a single positive lens (lens name L31, enlargement side name 301, The name of the reduced side surface is 302). A cover glass CG (C01 is an enlarged side surface and C02 is a reduced side surface) which is a component of a light valve such as a DMD with a slight air gap between the reduced side of the third lens group LG3 and the light valve surface. ) Is arranged. The third lens group LG3 is fixed during zooming operation, and the first lens group LG1 is enlarged from the wide-angle end to the intermediate area from the enlargement side to the reduction side, and from the intermediate area to the telephoto end is enlarged from the reduction side. The second lens unit LG2 moves on the optical axis in the lateral direction, and the entire lens system is zoomed by moving on the optical axis from the reduction side to the enlargement side from the wide-angle end to the telephoto end.
As is well known, the aspherical surface used in each embodiment has an aspherical formula when taking the Z axis in the optical axis direction and the Y axis in the direction orthogonal to the optical axis:
Z = (Y ² / r) / [1 + √ {1- (1 + K) (Y / r) ² }]
+ A ・ Y ⁴ + B ・ Y ⁶ + C ・ Y ⁸ + D ・ Y ¹⁰ ...
Is a curved surface obtained by rotating the curve given by 回 り around the optical axis, giving a paraxial radius of curvature: r, conic constant: K, and higher order aspherical coefficients: A, B, C, D, etc. Define In the notation of the conic constant and the higher-order aspheric coefficient in the table, “E and the number following it” represent “power of 10”. For example, “E-4” means 10 ⁻⁴ , and this numerical value may be multiplied by the immediately preceding numerical value.

[Example 1]
Table 1 shows numerical examples of the first embodiment of the compact zoom lens according to the present invention. FIG. 1 is a diagram showing the lens configuration, and FIG. 2 is a diagram showing various aberrations thereof.
In the table and drawings, f is the focal length of the zoom lens system, F _no is the F-number, 2 [omega a total angle of view of the zoom lens. Further, r is a radius of curvature, d is a lens thickness or a lens interval, n _d is a refractive index with respect to the d line, and ν _d is an Abbe number of the d line (however, a numerical value that changes due to the focusing operation in the table is 101 plane) The numerical value in the in-focus state with the object distance from 1700 mm). CA1, CA2, and CA3 in the spherical aberration diagrams in the various aberration diagrams are aberration curves at wavelengths of CA1 = 550.0 nm, CA2 = 450.0 nm, and CA3 = 620.0 nm, respectively. In the astigmatism diagram, S indicates sagittal and M indicates meridional. In addition, unless otherwise specified throughout, the wavelength used for calculation of various values is CA1 = 550.0 nm.

[Example 2]
Table 2 shows numerical examples of the second embodiment of the compact zoom lens according to the present invention. FIG. 3 is a diagram showing the lens configuration, and FIG. 4 is a diagram showing various aberrations thereof.

[Example 3]
Table 3 shows numerical examples of the third embodiment of the compact zoom lens according to the present invention. FIG. 5 is a diagram showing the lens configuration, and FIG. 6 is a diagram showing various aberrations.

  Next, Table 4 collectively shows values corresponding to the conditional expressions (1) to (15) with respect to the first to third embodiments.

  As is clear from Table 4, the numerical values for the first to fifth embodiments satisfy the conditional expressions (1) to (15) and are also clear from the aberration diagrams in the respective embodiments. Thus, each aberration is corrected well.

Claims (6)

The first lens group having a negative refractive power as a whole, the second lens group having a positive refractive power as a whole, and the third lens group having a positive refractive power as a whole in order from the magnification side, The lens group is composed of, in order from the magnifying side, five lenses: a meniscus lens convex on the magnifying side, a negative lens, a lens having a positive refracting power, a negative lens, and a positive lens. The second lens group includes, in order from the enlargement side, a positive lens, and a concave meniscus negative lens, a positive lens, a negative lens, and a positive lens on the enlargement side. The group is a zoom lens capable of zooming comprising a single positive lens, and the third lens group is fixed during zooming operation, and the first lens group extends from the wide-angle end to an intermediate region. Up to the zoom-out side, and from the middle to the telephoto end Over the optical axis in the direction from the reduction side to the enlargement side, and the second lens group moves on the optical axis in the direction from the reduction side to the enlargement side from the wide-angle end to the telephoto end. The following conditional expression (1) is satisfied with respect to the distance on the optical axis from the magnifying side surface of the lens arranged closest to the magnifying side in the first lens group at the wide angle end to the in-focus position, and The following conditional expression (2) is satisfied with respect to the positional relationship between the second lens group and the third lens group at the end, and the following conditional expression (3) is satisfied with respect to the magnification at the wide angle end of the second lens group. The power of the first lens group satisfies the following conditional expression (4), the magnification of the second lens group at the telephoto end satisfies the following conditional expression (5), and the second lens Arranged on the 4th sheet from the group expansion side Features and to Luz Murenzu that it satisfies the following conditional expression (6) with respect to a power of the lens.
(1) 7.0 <TL / _fw <10.0
(2) 1.8 < _dIIw / _fw <2.5
(3) −1.0 <m _{II w} <−0.5
_{(4) -1.0 <f w /} f I <-0.5
(5) 1.4 <m _{II T} / m _{II w} <2.8
_{(6) -0.7 <f w /} f 9 <-0.6
However,
TL: Distance on the optical axis from the magnifying side surface of the lens arranged closest to the magnifying side in the first lens unit at the wide angle end to the in-focus position (according to the magnifying side object distance of 1700 mm from the magnifying side most of the first lens unit) Out of focus)
f _w : Combined focal length of the entire lens system at the wide-angle end (focused state on the enlargement side object distance of 1700 mm from the most enlargement side surface of the first lens group)
d _{II w} : Air distance between the second lens group and the third lens group at the wide-angle end
f _I : Composite focal length of the first lens group m _{II w} : Second lens group magnification at the wide angle end m _{II T} : Second lens group magnification at the telephoto end f ₉ : Four from the magnification side of the second lens group The focal length of the lens placed in the eye In FIG Murenzu of claim 1, wherein, with respect to the dimensions of the optical axis of the first lens group, and satisfies the following conditional expression (7), the lens disposed most magnification side in the first lens group The following conditional expression (8) is satisfied with respect to power, and the following conditional expression (9) is satisfied with respect to the shape of the reduction side surface of the lens disposed on the most magnifying side in the first lens group, and the first lens It is characterized in that the following conditional expression (10) is satisfied with respect to the dispersion characteristics of the glass material used for each lens constituting the group.
_{(7) 1.4 <L I /} f w <2.3
_{(8) -0.7 <f w /} f 1 <-0.2
(9) 0.8 <f _w / r ₂ <1.5
(10) 16 <(V ₁ + V ₂ + V ₄ ) / 3- (V ₃ + V ₅ ) / 2
However,
L _I : Distance f ₁ on the optical axis between the enlargement side surface of the lens arranged closest to the enlargement side in the first lens group and the reduction side surface of the lens arranged closest to the reduction side in the first lens group f ₁ : first lens group The focal length r _{2 of} the lens arranged closest to the magnification side: radius of curvature V ₁ of the reduction side of the lens arranged closest to the magnification side in the first lens group V ₁ : negative arranged closest to the magnification side in the first lens group Lens Abbe number V ₂ : Abbe number of the negative lens disposed on the second lens from the magnification side in the first lens group V ₃ : Abbe number of the positive lens disposed on the third lens from the magnification side in the first lens group V ₄ : Abbe number of the negative lens disposed on the fourth lens from the magnification side in the first lens group V ₅ : Abbe number of the positive lens disposed on the most reduction side in the first lens group In FIG Murenzu of the claims 1 and 2 wherein, the second sheet a focusing operation is achieved by moving the first lens group in the optical axis direction, in the first lens group which makes up the first lens group Conditional expression (11) is satisfied with respect to the lens disposed in the lens, and at least one surface of the second lens disposed in the first lens group has an aspherical shape.
(11) −0.5 <f _w / f ₂
However,
f ₂ : Focal length of the second lens from the magnification side in the first lens group In FIG Murenzu of claim 1, wherein the second lens group, a positive lens in order from the magnifying side, a negative lens element concave meniscus shape on the magnification side, a positive lens, a negative lens, is composed of five positive lenses, Each of the five lenses constituting the second lens group satisfies the following conditional expression (12) with respect to the shape on the magnification side of the lens arranged closest to the magnification side in the lens group constituting the second lens group. The following conditional expression (13) is satisfied with respect to the dispersion characteristics of the glass material used for the second lens group, and the following conditional expression (14) is satisfied with respect to the dispersion characteristics of the glass material arranged on the most reduction side of the second lens group. It is characterized by that.
_{(12) 0.3 <f w /} r II 1 <0.9
_{(13) 25 <(V 6} + V 8 + V 10) / 3- (V 7 + V 9) / 2
(14) 69 <V ₁₀
However,
r _{II 1} : radius of curvature V ₆ of the magnifying side surface of the lens arranged closest to the magnifying side of the second lens group V ₆ : Abbe number V _{7 of the} positive lens laid out closest to the magnifying side of the second lens group In the second lens group, the Abbe number V _{8 of} the second lens arranged from the magnifying side is V ₈ : The Abbe number V _{9 of the} positive lens arranged from the magnifying side in the second lens group is V ₉ : Abbe number V _{10 of the} negative lens arranged in the fourth lens: Abbe number of the positive lens arranged closest to the reduction side in the second lens group In FIG Murenzu of claim 4, wherein, at least one surface of the lens disposed on the second sheet from the enlargement side of the second lens group is aspherical, it is disposed closest to the contracting side of the second lens group The following conditional expression (15) is satisfied with respect to the shape of the reduction side surface of the lens.
(15) −0.8 <f _W / r _{II 10} <−0.2
However,
r _{II 10} : radius of curvature of the reduction side surface of the lens arranged closest to the reduction surface side of the second lens group The projector apparatus is characterized in that is equipped with a described LUZ Murenzu claims 1 to one of the preceding claims 5 Neu Zureka.

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