Projection lens system and image projection device

A projection lens system projects an image of a reduction side into a magnification side in an image projection device, a back glass being disposed on the reduction side. In the projection lens system, all of one or more negative lenses that satisfy, in a surface on the reduction side or a surface on the magnification side, condition |h/H|<2.0 defined by height h of a most off-axis principal ray and height H of an axial ray passing through a highest pupil position satisfy conditions Tn≥98.5% and Dn/Db≤0.05 defined by transmittance Tn, thickness Dn of the negative lens on an optical axis, and total thickness Db of the back glass.

TECHNICAL FIELD

The present disclosure relates to a projection lens system that projects an image of a reduction side into a magnification side, and an image projection device including the projection lens system.

BACKGROUND ART

PTL 1 discloses an optical system for successfully correcting chromatic aberrations and reducing a shift in focus position due to a temperature change in an image projection device and an imaging device. In the optical system of PTL 1, at least two positive lenses in which the Abbe number, anomalous dispersion property, rate of change in refractive index with respect to temperature changes, and the like are set in appropriate ranges are disposed closer to the reduction side than a diaphragm. As a result, the shift in the focus position caused by the change in refractive index due to the temperature change can be reduced, while the axial chromatic aberration is successfully corrected by increasing the width of an axial light flux. PTL 1 describes that a lamp used as a light source is a cause of high temperature in the image projection device.

CITATION LIST

Patent Literature

SUMMARY

The present disclosure provides a projection lens system and an image projection device that can improve the image quality of an image when the brightness of the image projection device is increased.

A projection lens system according to the present disclosure is a lens system that projects an image of a reduction side into a magnification side in an image projection device, a back glass being disposed on the reduction side. The projection lens system includes one or more negative lenses. Each of the one or more negative lenses has a surface on the reduction side and a surface on the magnification side. Each of the one or more negative lenses satisfies following condition (1) in the surface on the reduction side or the surface on the magnification side. All of the one or more negative lenses satisfy following conditions (2) and (3),
|h/H|<2.0  (1)
Tn≥98.5%  (2)
Dn/Db≤0.05  (3)

where

h indicates a height of a most off-axis principal ray,

H indicates a height of an axial ray passing through a highest pupil position,

Tn indicates a transmittance of light having a wavelength of 460 nm when a lens material of the one or more negative lenses has a thickness of 10 mm,

Dn indicates a thickness of the one or more negative lenses on an optical axis, and

Db indicates a total thickness of the back glass.

An image projection device according to the present disclosure includes the projection lens system described above and an image forming element. The image forming element forms an image.

According to the projection lens system and the image projection device according to the present disclosure, it is possible to improve the image quality of an image when the brightness of the image projection device is increased.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments will be described below in detail with reference to the drawings as appropriate. Here, excessively detailed description will be omitted in some cases. For example, detailed description of already well-known matters and duplicated description of the substantially same configurations will be omitted in some cases. This is to prevent the following description from becoming unnecessarily redundant, thereby facilitating the understanding of those skilled in the art.

Here, the applicant provides the accompanying drawings and the following description such that those skilled in the art can fully understand the present disclosure, and therefore, does not intend to limit the subject matters described in the claims by the accompanying drawings and the following description.

First Exemplary Embodiment

Hereinafter, a first exemplary embodiment of a projection lens system and an image projection device according to the present disclosure will be described with reference to the drawings.

An outline of an image projection device including a projection lens system according to the first exemplary embodiment of the present disclosure will be described with reference toFIG.1.FIG.1is a block diagram illustrating image projection device1according to the present exemplary embodiment.

Image projection device1according to the present exemplary embodiment is, for example, a high brightness projector having a light output of 20,000 lumens or more. In image projection device1, as illustrated inFIG.1, image light3showing various images2is generated by using image forming element11and the like, and image light3enters projection lens system PL. Projection lens system PL emits projection light35so as to magnify image2of entering image light3. Projection light35from projection lens system PL projects projection image20obtained by magnifying image2on external screen4or the like.

In image projection device1as described above, it is required to increase brightness so as to project projection image20more brightly. In increasing the brightness of image projection device1, it is assumed that image quality of projection image20is degraded by following factors.

That is, it is assumed in image projection device1that, when image light3having high brightness travels in projection lens system PL, a significant temperature change occurs in particular lens element Ln near diaphragm A or the like in projection lens system PL. The temperature change of lens element Ln changes a shape and a refractive index of lens element Ln, and thus may have various influences on performance of projection lens system PL, such as a shift in focus position, occurrence of spherical aberrations, and a variation in back focus.

In addition, the heat distribution of lens element Ln due to image light3may occur either uniformly or locally. It is considered that an influence of heat, such as a shift direction of the focus position, in a uniform case is different from that in a local case. As described above, in increasing the brightness of image projection device1, it is assumed that the performance of projection lens system PL becomes unstable due to the influence of heat according to the brightness of image2to be projected, and the image quality of projection image is degraded.

Consequently, in the present exemplary embodiment, projection lens system PL is configured so as to reduce the influence of heat due to image light3with high brightness. As a result, it is possible to reduce the influence of heat in increasing the brightness of image projection device1, stabilize the performance of projection lens system PL, and improve the image quality of projection image20.

2. About Image Projection Device

A configuration of image projection device1according to the present exemplary embodiment will be described below with reference toFIG.1.

As illustrated inFIG.1, image projection device1according to the present exemplary embodiment includes light source10, image forming element11, transmission optical system12, and projection lens system PL. Image projection device1is configured with, for example, a DLP system. The light output of image projection device1may be more than or equal to 30,000 lumens.

Light source10is, for example, a laser light source. Light source10includes, for example, a blue LD (semiconductor laser) element and has a peak wavelength near 450 nm. Light source10emits white illumination light30by, for example, combining various colors. Illumination light30is irradiated to image forming element11via transmission optical system12with a uniform illuminance distribution. Light source10may include a Koehler illumination optical system.

Image forming element11is, for example, a digital mirror device (DMD). Image forming element11has, for example, an image forming surface including a mirror element for each pixel, and forms image2on the image forming surface based on an external video signal or the like. Image forming element11spatially modulates illumination light30on the image forming surface to generate image light3. Image light3has directionality for each pixel on the image forming surface, for example.

Image projection device1may include a plurality of image forming elements11such as three chips corresponding to RGB. Image forming element11is not limited to the DMD and may be, for example, a liquid crystal element. In this case, image projection device1may be configured with a 3LCD system or an LCOS system.

Transmission optical system12includes a translucent optical element and the like, and is disposed between image forming element11and projection lens system PL. Transmission optical system12guides illumination light30from light source10to image forming element11. Further, transmission optical system12guides image light3from image forming element11to projection lens system PL. Transmission optical system12may include various optical elements such as a total internal reflection (TIR) prism, a color separation prism, a color combination prism, an optical filter, a parallel plate glass, a crystal low-pass filter, and an infrared cut filter. Hereinafter, the optical element in transmission optical system12is referred to as “back glass” in some cases.

Projection lens system PL is mounted on image projection device1, for example, as a module. Hereinafter, in projection lens system PL, a side facing outside of image projection device1is referred to as a “magnification side”, and a side opposite to the magnification side is referred to as a “reduction side”. Various back glasses of transmission optical system12are disposed on the reduction side of projection lens system PL.

Projection lens system PL includes a plurality of lens elements Ln and diaphragm A. A number of lens elements Ln is, for example, more than or equal to 15. This makes it possible to successfully correct various aberrations in projection lens system PL. Diaphragm A is, for example, an aperture diaphragm. In projection lens system PL, an aperture degree of diaphragm A is fixed in advance to, for example, an open state. Projection lens system PL may be incorporated in image projection device1without being modularized. Hereinafter, details of projection lens system PL according to the present exemplary embodiment will be described.

3. About Projection Lens System

In the first exemplary embodiment, first to third examples in which projection lens system PL configuring a negative-lead zoom lens system will be described as a specific example. The negative-lead zoom lens system is a lens system that includes a plurality of lens groups that move during zooming and in which a lens group on a most magnification side has a negative power.

3-1. First Example

Projection lens system PL1of the first example will be described with reference toFIGS.2to3.

FIG.2is a lens arrangement diagram in various states of projection lens system PL1according to the first example. Following lens arrangement diagrams each illustrate an arrangement of various lenses when a whole system such as projection lens system PL1is focused at 4,000 mm. A left side in the figure is a magnification side or object side of the whole system. A right side in the figure is a reduction side or image side of the whole system. In each figure, a position of image plane S is illustrated on a rightmost side, that is, on the reduction side. Image plane S corresponds to the image forming surface of image forming element11.

FIG.2(a)is a lens arrangement diagram at a wide-angle end of projection lens system PL1according to the first example.FIG.2(b)is a lens arrangement diagram at an intermediate position of projection lens system PL1according to the first example.FIG.2(c)is a lens arrangement diagram at a telephoto end of projection lens system PL1according to the first example. The wide-angle end means a shortest focal length state where the whole system has shortest focal length fw. The intermediate position means an intermediate focal length state between the wide-angle end and the telephoto end. The telephoto end means a longest focal length state where the whole system has longest focal length ft. Based on focal length fw at the wide-angle end and focal length ft at the telephoto end, a focal length at the intermediate position is defined as fm=√(fw×ft).

Line arrows indicated betweenFIG.2(a)andFIG.2(b)are lines obtained by connecting positions of lens groups at the wide-angle end, the intermediate position, and the telephoto end in this order from a top of the figure. The wide-angle end and the intermediate position, and the intermediate position and the telephoto end are simply connected by straight lines, which is different from an actual movement of each lens group. Symbols (+) and (−) attached to reference signs of the respective lens groups indicate positive and negative of the power of each lens group.

Projection lens system PL1of the first example includes 18 lens elements L1to L18constituting three lens groups G1to G3. As illustrated inFIG.2(a), first, second, and third lens groups G1, G2, G3are arranged in order from the magnification side to the reduction side of projection lens system PL1. Projection lens system PL1functions as a zoom lens system by moving each of first to third lens groups G1to G3along an optical axis of projection lens system PL1during zooming.

In projection lens system PL1, first to eighteenth lens elements L1to L18are arranged in order from the magnification side to the reduction side. Each of first to eighteenth lens elements L1to L18configures a positive lens or a negative lens. The positive lens has a biconvex shape or a positive meniscus shape and thus has a positive power. The negative lens has a biconcave shape or a negative meniscus shape and thus has a negative power.

First lens group G1includes first to seventh lens elements L1to L7, and has a negative power. First lens element L1has a negative meniscus shape, and is arranged with its convex surface facing the magnification side. Second lens element L2has a biconvex shape. Third lens element L3has a positive meniscus shape, and is arranged with its convex surface facing the magnification side. Fourth lens element L4has a negative meniscus shape, and is arranged with its convex surface facing the magnification side. Fifth lens element L5has a negative meniscus shape, and is arranged with its convex surface facing the magnification side. Sixth lens element L6has a biconcave shape. Seventh lens element L7has a biconvex shape.

Second lens group G2includes eighth to tenth lens elements L8to L10, and has a positive power. Eighth lens element L8has a positive meniscus shape, and is arranged with its convex surface facing the magnification side. Ninth lens element L9has a negative meniscus shape, and is arranged with its convex surface facing the magnification side. Tenth lens element L10has a biconvex shape.

Third lens group G3includes eleventh to eighteenth lens elements L11to L18, and has a positive power. Diaphragm A is disposed on the magnification side of eleventh lens element L11. Eleventh lens element L11has a biconcave shape. Twelfth lens element L12has a biconvex shape. Thirteenth lens element L13has a positive meniscus shape, and is arranged with its convex surface facing the reduction side. Fourteenth lens element L14has a biconvex shape. Fifteenth lens element L15has a biconcave shape. Sixteenth lens element L16has a biconvex shape. Seventeenth lens element L17has a negative meniscus shape, and is arranged with its convex surface facing the reduction side. Eighteenth lens element L18has a biconvex shape.

FIGS.2(a) to2(c)illustrate, as an example of transmission optical system12, three back glasses L19, L20, L21arranged between eighteenth lens element L18on the most reduction side in projection lens system PL1and image plane S. Back glasses L19to L21are, for example, various prisms, filters, cover glasses, and the like. In each figure, back glasses L19to L21for one image plane S corresponding to one image forming element11are illustrated for convenience of description. Projection lens system PL1can be used for various transmission optical systems12when a plurality of image forming elements11are used.

Projection lens system PL1constitutes a substantially telecentric system on the reduction side to which light from image plane S enters through back glasses L19to L21. It is thus possible to reduce a color shift and the like due to a coating of a prism in transmission optical system12. Further, the light from image plane S of image forming element11can be efficiently taken into projection lens system PL1.

FIG.3is an aberration diagram illustrating various longitudinal aberrations of projection lens system PL1according to the first example. The following aberration diagrams exemplify various longitudinal aberrations in a focused state at 4,000 mm.

FIG.3(a)illustrates aberrations at the wide-angle end of projection lens system PL1according to the first example.FIG.3(b)illustrates aberrations at the intermediate position of projection lens system PL1according to the first example.FIG.3(c)illustrates aberrations at the telephoto end of projection lens system PL1according to the first example.FIGS.3(a),3(b),3(c)each include a spherical aberration diagram showing a spherical aberration on horizontal axis “SA (mm)”, an astigmatism diagram showing an astigmatism on horizontal axis “AST (mm)”, and a distortion aberration diagram showing a distortion aberration on horizontal axis “DIS (%)” in this order from the left side in the respective figures.

In each spherical aberration diagram, vertical axis “F” represents an F number. Also, a solid line denoted by “d-line” in the figures indicates properties of a d-line. A broken line denoted by “F-line” indicates properties of an F-line. A broken line denoted by “C-line” indicates properties of a C-line. In the respective astigmatism diagrams and the respective distortion aberration diagrams, vertical axis “H” indicates an image height. In addition, a solid line denoted by “s” in the figures indicates properties of a sagittal plane. A broken line denoted by “m” indicates properties of a meridional plane.

The aberrations in various states illustrated inFIGS.3(a),3(b),3(c)are based on a first numerical example in which projection lens system PL1of the first example is specifically implemented. The first numerical example of projection lens system PL1will be described later.

3-2. About Measures for Heat in Increasing Brightness

Using projection lens system PL1of the first example described above, measures for heat of projection lens system PL1in increasing the brightness of image projection device1according to the present exemplary embodiment will be described with reference toFIGS.4to6.FIG.4is a table illustrating sufficiency of various conditions in projection lens system PL1according to the first example.

The table illustrated inFIG.4shows which of all lens elements L1to L18in projection lens system PL1of the first example satisfies following conditions (1) to (8). The symbol “∘” in items for each lens indicates that the corresponding condition is satisfied, and the blank indicates that the corresponding condition is not satisfied. In addition, the symbol “/” indicates that the lens is not a target lens for determining the corresponding condition from the viewpoint of the power of the lens or the like.

FIG.4also shows various parameters related to conditions (1) to (8). Various parameters include |h/H| to be described later, a lens transmittance, Dn/Db, vd, |fn/f|, and dn/dt. Regarding the power of the lens, the positive lens is denoted by “P”, and the negative lens is denoted by “N”. Further, lens materials of the lens elements L1to L18are also shown.

In the present exemplary embodiment, all negative lenses that satisfy condition (1) in projection lens system PL1are configured to satisfy condition (2) and condition (3). Condition (1) is a condition for specifying a lens that is easily affected by heat of image light3in image projection device1and easily affects the performance of projection lens system PL1.

Condition (1) is expressed by a following inequality.
|h/H|<2.0  (1)

Here, h indicates the height of a most off-axis principal ray on a surface on the magnification side or a surface on the reduction side of a lens that is a determination target. H indicates a maximum height of an axial ray on the same surface of the lens. It is considered that a lens having a value exceeding an upper limit value defined by the right side of the above inequality does not cause a concentration of rays to be described later and is less likely to be affected by heat. Whether condition (1) is satisfied or not is determined by whether a minimum value of |h/H| on the left side of the above inequality between the wide-angle end and the telephoto end of projection lens system PL1is smaller than the upper limit value. The heights h and H of rays for each lens in condition (1) will be described with reference toFIG.5.

FIG.5is an optical path diagram illustrating an optical path of a ray in projection lens system PL1according to the first example.FIG.5illustrates a most off-axis principal ray31and an axial ray32passing through a highest pupil position in projection lens system PL1. Most off-axis principal ray31is emitted from a position farthest from optical axis5on image plane S and passes through a center position of diaphragm A. A light flux of the axial ray is emitted from the position of optical axis5on image plane S. In the light flux of the axial ray, axial ray32passing through the highest pupil position is defined by a ray passing through the pupil position, that is, the highest position of diaphragm A. The heights of various rays are based on optical axis5.

FIG.5illustrates heights h, H of rays31,32in first lens element L1and ninth lens element L9in projection lens system PL1of the first example.FIG.5illustrates heights h, H using positions where respective rays31,32pass through physical surfaces of lens elements L1, L9. Heights h, H of rays31,32may be measured on a main surface on an optical magnification side or an optical reduction side of the lens.

As illustrated inFIG.4, in the first example, first lens element L1does not satisfy condition (1), whereas ninth lens element L9satisfies condition (1). As illustrated inFIG.5, in first lens element L1, height h of most off-axis principal ray31is larger than height H of axial ray32. On the other hand, in ninth lens element L9, height h of most off-axis principal ray31is much smaller than height H of axial ray32.

FIG.6illustrates an enlarged view of a vicinity of ninth lens element L9illustrated inFIG.5. In first lens element L1ofFIG.5, most off-axis principal ray31is separated from axial ray32. On the other hand, in ninth lens element L9, most off-axis principal ray31overlaps axial ray32near a center of ninth lens element L9, as illustrated inFIG.6. As described above, it is assumed in the lens satisfying condition (1) that rays of light emitted at various points on image plane S are concentrated near the center of the lens and thus a local temperature change is likely to occur.

Consequently, according to the present exemplary embodiment, various conditions for reducing the influence of heat are imposed on a lens that satisfies condition (1) and is easily affected by heat, thus stabilizing the performance of projection lens system PL1. In particular, a negative lens is assumed to be affected by heat, for example, a focus position is sensitively shifted by the local temperature change. Following conditions (2) and (3) are thus imposed on all negative lenses that satisfy condition (1).

Condition (2) is expressed by the following inequality.
Tn≥98.5%  (2)

Here, Tn indicates a transmittance at which light having a wavelength of 460 nm passes through a lens material of a negative lens having a thickness of 10 mm. The transmittance is, for example, an internal transmittance. In general, the lens material is more likely to absorb energy of light having a shorter wavelength, and a light source having a particularly strong peak intensity for blue light is usually used in an image projection device. A reference transmittance is thus set to the wavelength mentioned above.

According to condition (2), it is possible to achieve high transmittance Tn of the negative lens and reduce energy absorbed by the negative lens when a ray passes through the negative lens. If transmittance Tn of the negative lens is less than a lower limit value of condition (2), that is, 98.5%, the energy absorbed by the negative lens becomes large, and the influence of heat is excessively exerted on the negative lens. Consequently, transmittance Tn of the negative lens is preferably more than or equal to 99%.

Condition (3) is expressed by the following inequality.
Dn/Db≤0.05  (3)

Here, Dn indicates a thickness of a portion of the negative lens located on the optical axis. Db indicates a total thickness of various back glasses arranged on the reduction side of projection lens system PL1.FIG.5illustrates thickness Dn of ninth lens element L9and total thickness Db of back glasses L19, L20, L21in the first example. More specifically, total thickness Db is a sum of the thickness of back glass L19, the thickness of the back glass L20, and the thickness of back glass L21.

According to condition (3), by making the negative lens thinner, absorption of energy by the negative lens when a rays pass through the negative lens can be reduced. If thickness Dn of the negative lens exceeds the upper limit value of condition (3), that is, 0.05×Db, the energy absorbed by the negative lens becomes large, and the influence of heat is excessively exerted on the negative lens. Thickness Dn of the negative lens is preferably less than or equal to 0.035×Db.

Returning toFIG.4, in projection lens system PL1of the first example, sixth to eighteenth lens elements L6to L18satisfy condition (1). In the present exemplary embodiment, all the lenses on the reduction side of diaphragm A in projection lens system PL1may satisfy condition (1). As a result, a distance between diaphragm A and the lens on the reduction side can be reduced, and a total length of projection lens system PL1can also be reduced.

In the first example, among sixth to eighteenth lens elements L6to L18satisfying condition (1), sixth lens element L6, ninth lens element L9, eleventh lens element L11, fifteenth lens L15, and seventeenth lens element L17are negative lenses. As illustrated inFIG.4, all the negative lenses satisfying condition (1) described above satisfy conditions (2) and (3). As a result, it is possible to reduce the influence of heat on the negative lens, which easily affects the performance of projection lens system PL1, thus stabilizing the performance of projection lens system PL1.

In the present exemplary embodiment, all negative lenses satisfying condition (1) may further satisfy following condition (4). In projection lens system PL1of the first example, all the negative lenses satisfying condition (1) described above satisfy condition (4), as illustrated inFIG.4.

Condition (4) is expressed by the following inequality.
|fn/fw|>1.2  (4)

Here, fn indicates a focal length of one negative lens. As described above, fw indicates the focal length at the wide-angle end of the whole system.

According to condition (4), it is possible to achieve long focal length fn of the negative lens, thus reducing the influence of heat such as a shift in focus position. If the negative lens has a value less than the lower limit value of condition (4), the power of the negative lens or the like may sensitively vary depending on image2to be projected. By weakening the power of the negative lens specified by condition (1) according to condition (4), stability of the performance of projection lens system PL1can be improved.

Moreover, in the present exemplary embodiment, at least one of all the negative lenses may satisfy condition (5). In projection lens system PL1of the first example, as illustrated inFIG.4, two lenses, that is, first lens element L1and seventeenth lens element L17satisfy condition (5).

Condition (5) is expressed by the following inequality.
vn<40  (5)

Here, vn is the Abbe number of a lens material of the negative lens. For example, Abbe number vd based on the d line can be adopted as the Abbe number.

In general, a lens material having a higher Abbe number tends to have a higher transmittance and is thermally advantageous. However, it is difficult to successfully correct the chromatic aberration of projection lens system PL1only with the negative lens having a value that exceeds the upper limit value of condition (5). By including a negative lens that satisfies condition (5) in projection lens system PL1, it is possible to successfully correct the chromatic aberration while achieving heat resistance when the brightness is increased. In particular, the chromatic aberration can be successfully corrected when a high zoom or a wide angle is achieved in projection lens system PL1. It is preferable that Abbe number vn of at least one negative lens is smaller than 36.

Moreover, in the present exemplary embodiment, all the positive lenses satisfying condition (1) may satisfy following condition (6). As illustrated inFIG.4, in projection lens system PL1of the first example, the positive lenses satisfying condition (1) are seventh lens element L7, eighth lens element L8, tenth lens element L10, twelfth lens element L12, thirteenth lens element L13, fourteenth lens element L14, sixteenth lens element L16, and eighteenth lens element L18. In the first example, all the positive lenses satisfying condition (1) described above satisfy condition (6).

Condition (6) is expressed by the following inequality.
Tp>98.5%  (6)

Here, Tp indicates the transmittance of light having a wavelength of 460 nm when a lens material of the positive lens has a thickness of 10 mm, like transmittance Tn of the negative lens.

According to condition (6), it is possible to achieve high transmittance Tp also in the positive lens, thus further stabilizing the performance of projection lens system PL1. If transmittance Tp of the positive lens is less than the lower limit value of condition (6), the amount of energy absorbed becomes large, and thus the influence of heat is concerned. Transmittance Tp of the positive lens is preferably more than or equal to 99%.

Moreover, in the present exemplary embodiment, at least four of the positive lenses satisfying condition (1) may satisfy following condition (7). In projection lens system PL1of the first example, as illustrated inFIG.4, five lens elements, that is, eighth lens element L8, tenth lens element L10, fourteenth lens element L14, sixteenth lens element L16, and eighteenth lens element L18satisfy condition (7).

Condition (7) is expressed by the following inequality.
dn/dt<−4.5×10−6(7)

Here, dn/dt indicates a temperature coefficient of a relative refractive index of a lens material of the positive lens at room temperature. The room temperature ranges from 20° C. to 30° C., for example.

In a positive lens having a negative temperature coefficient of the refractive index, the influence of a change in shape and the influence of a change in refractive index may be offset when the focus position is shifted due to a local temperature change. According to condition (7), the stability of the performance of projection lens system PL1can be improved, and the chromatic aberration can be successfully corrected.

Moreover, in the present exemplary embodiment, at least one of the positive lenses satisfying condition (1) may satisfy following condition (8). In projection lens system PL1of the first example, as illustrated inFIG.4, two lenses, that is, twelfth lens element L12and thirteenth lens element L13satisfy condition (8).

Condition (8) is expressed by the following inequality.
vp<40  (8)

Here, vp indicates the Abbe number of the lens material of the positive lens.

If all the positive lenses satisfying condition (1) exceed the upper limit value of condition (8), it becomes difficult to successfully correct the chromatic aberration in projection lens system PL1. According to condition (8), it is possible to successfully correct the chromatic aberration especially in a case of a high zoom or a wide angle while achieving the heat resistance when the brightness is increased. Abbe number vp of at least one positive lens is preferably smaller than 36.

3-3. Second Example

The measures for high brightness described above can be implemented not only in projection lens system PL1of the first example but also in any projection lens system. Projection lens system PL2of a second example will be described with reference toFIGS.7to9.

FIG.7is a lens arrangement diagram in various states of projection lens system PL2according to the second example.FIGS.7(a),7(b),7(c)are lens arrangement diagrams at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL2, respectively, similarly toFIGS.2(a) to2(c).

Projection lens system PL2of the second example includes 16 lens elements L1to L16. In projection lens system PL2, first to sixteenth lens elements L1to L16are arranged in order from the magnification side to the reduction side, as in the first example. Projection lens system PL2of the second example includes three lens groups G1to G3to constitute a zoom lens system, as in the first example.FIGS.7(a) to7(c)illustrate back glasses L17to L19as an example of transmission optical system12.

In projection lens system PL2of the second example, first lens group G1includes first to sixth lens elements L1to L6, and has a negative power. First lens element L1has a negative meniscus shape, and its convex surface faces the magnification side. Second lens element L2has a biconvex shape. Third lens element L3has a negative meniscus shape, and its convex surface faces the magnification side. Fourth lens element L4has a negative meniscus shape, and its convex surface faces the magnification side. Fifth lens element L5has a biconcave shape. Sixth lens element L6has a biconvex shape.

Second lens group G2includes seventh and eighth lens elements L7, L8, and has a positive power. Seventh lens element L7has a negative meniscus shape, and its convex surface faces the magnification side. Eighth lens element L8has a biconvex shape. Seventh lens element L7and eighth lens element L8are bonded to each other.

Third lens group G3includes ninth to sixteenth lens elements L9to L16, and has a positive power. Diaphragm A is disposed on the magnification side of ninth lens element L9. Ninth lens element L9has a biconcave shape. Tenth lens element L10has a biconvex shape. Eleventh lens element L11has a biconvex shape. Twelfth lens element L12has a biconvex shape. Thirteenth lens element L13has a biconcave shape. Fourteenth lens element L14has a biconvex shape. Fifteenth lens element L15has a negative meniscus shape, and its convex surface faces the reduction side. Sixteenth lens element L16has a biconvex shape.

FIG.8is an aberration diagram illustrating longitudinal aberrations of projection lens system PL2according to the second example.FIGS.8(a),8(b),8(c)illustrate aberrations at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL2, respectively, similarly toFIGS.3(a) to3(c). The aberrations illustrated inFIGS.8(a) to8(c)are based on a second numerical example to be described later.

FIG.9illustrates sufficiency of conditions (1) to (8) in projection lens system PL2according to the second example. The table illustrated inFIG.9shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L16in projection lens system PL2of the second example, as in the first example. Projection lens system PL2of the second embodiment can also improve the image quality of projection image20when the brightness of image projection device1is increased.

3-4. Third Example

Projection lens system PL3of a third example will be described with reference toFIGS.10to12.

FIG.10is a lens arrangement diagram in various states of projection lens system PL3according to the third example.FIGS.10(a),10(b),10(c)are lens arrangement diagrams at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL3, respectively, similarly toFIGS.2(a) to2(c).

Projection lens system PL3of the third example includes 17 lens elements L1to L17. In projection lens system PL3, first to seventeenth lens elements L1to L17are arranged in order from the magnification side to the reduction side, as in the first example. Projection lens system PL3of the third example includes three lens groups G1to G3to constitute a zoom lens system, as in the first example.FIGS.10(a) to10(c)illustrate back glasses L18to L20as an example of transmission optical system12.

In projection lens system PL3of the third example, first lens group G1includes first to sixth lens elements L1to L6, and has a negative power. First lens element L1has a negative meniscus shape, and its convex surface faces the magnification side. Second lens element L2has a biconvex shape. Third lens element L3has a negative meniscus shape, and its convex surface faces the magnification side. Fourth lens element L4has a biconcave shape. Fifth lens element L5has a biconcave shape. Sixth lens element L6has a biconvex shape.

Second lens group G2includes seventh to ninth lens elements L7to L9, and has a positive power. Seventh lens element L7has a positive meniscus shape, and its convex surface faces the magnification side. Eighth lens element L8has a negative meniscus shape, and its convex surface faces the magnification side. Ninth lens element L9has a biconvex shape.

Third lens group G3includes tenth to seventeenth lens elements L10to L17, and has a positive power. Diaphragm A is disposed on the magnification side of tenth lens element L10. Tenth lens element L10has a biconcave shape. Eleventh lens element L11has a biconvex shape. Twelfth lens element L12has a biconvex shape. Thirteenth lens element L13has a biconvex shape. Fourteenth lens element L14has a biconcave shape. Fifteenth lens element L15has a biconvex shape. Sixteenth lens element L16has a negative meniscus shape, and its convex surface faces the reduction side. Seventeenth lens element L17has a biconvex shape.

FIG.11is an aberration diagram illustrating longitudinal aberrations of projection lens system PL3according to the third example.FIGS.11(a),11(b),11(c)illustrate aberrations at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL3, respectively, similarly toFIGS.3(a) to3(c). The aberrations illustrated inFIGS.11(a) to11(c)are based on a third numerical example to be described later.

FIG.12illustrates sufficiency of conditions (1) to (8) in projection lens system PL3according to the third example. The table illustrated inFIG.12shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L17in projection lens system PL3of the third example, as in the first example. Projection lens system PL3of the third example can also improve the image quality of projection image20when the brightness of image projection device1is increased.

3-5. About First to Third Examples

Projection lens systems PL1to PL3of the first to third examples described above can project image2on the reduction side in image projection device1to the magnification side as projection image20. Projection lens systems PL1to PL3constitute a zoom lens system including diaphragm A and a plurality of lens groups G1to G3. Lens group G1closest to the magnification side in lens groups G1to G3has a negative power. Negative-lead projection lens systems PL1to PL3satisfy following condition (9) in the present exemplary embodiment.

Condition (9) is expressed by the following inequality.
2<fr/fw<4.5  (9)

Here, fr indicates the focal length at the wide-angle end on the reduction side of diaphragm A. Condition (9) defines ratio fr/fw of focal length fr to focal length fw at the wide-angle end of the whole system.

Specifically, fr/fw=3.34 is satisfied in projection lens system PL1of the first example. In projection lens system PL2of the second example, fr/fw=3.73 is satisfied. In projection lens system PL3of the third example, fr/fw=2.74 is satisfied.

According to condition (9), the performance of projection lens systems PL1to PL3constituting the negative-lead type zoom lens system can be successfully achieved. If the ratio exceeds the upper limit value of condition (9), it becomes difficult to maintain telecentricity on the reduction side while keeping a long back focus. If the ratio is less than the lower limit value of condition (9), it becomes difficult to correct the aberration, and the image quality of projection image20projected on the magnification side may be degraded. Ratio fr/fw is preferably larger than 2.5 and less than 4.0.

Second Exemplary Embodiment

A second exemplary embodiment will be described below with reference to the drawings. While the first exemplary embodiment has described an example in which projection lens system PL constitutes a zoom lens system, projection lens system PL is not limited to the zoom lens system. The second exemplary embodiment will describe projection lens system PL configured to form an intermediate image therein.

Hereinafter, description of configurations and operations similar to those of image projection device1and projection lens system PL according to the first exemplary embodiment will be appropriately omitted, and fourth to sixth examples will be described as examples of projection lens system PL according to the present exemplary embodiment.

1. Fourth Example

Projection lens system PL4according to a fourth example of the present disclosure will be described with reference toFIGS.13to16.

FIG.13is a lens arrangement diagram of projection lens system PL4according to the fourth example.FIG.14is an aberration diagram illustrating longitudinal aberrations of projection lens system PL4according to the fourth example. The aberration diagram of the present exemplary embodiment includes a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in this order from the left side of the figure, as in the first exemplary embodiment. In the astigmatism diagram and the distortion aberration diagram according to the present exemplary embodiment, vertical axis “w” indicates a half angle of field.

FIGS.13,14illustrate the arrangement of various lenses and various aberrations, respectively in a focused state where a projection distance of projection lens system PL4according to the fourth example is 4,000 mm. A fourth numerical example corresponding to projection lens system PL4of the fourth example will be described later.

As illustrated inFIG.13, projection lens system PL4of the fourth example includes 22 lens elements L1to L22. In the present exemplary embodiment, first to twenty-second lens elements L1to L22in projection lens system PL4are arranged in order from the magnification side to the reduction side, as in the first exemplary embodiment. Further,FIG.13also illustrates back glasses L23to L25as an example of transmission optical system12.

In the present exemplary embodiment, first to twenty-second lens elements L1to L22in projection lens system PL4constitute magnification optical system51and relay optical system52. Magnification optical system51is located closer to the magnification side than relay optical system52is.

Magnification optical system51includes first to eleventh lens elements L1to L11, and has a positive power. First lens element L1has a negative meniscus shape, and its convex surface faces the magnification side. Second lens element L2has a negative meniscus shape, and its convex surface faces the magnification side. Third lens element L3has a negative meniscus shape, and its convex surface faces the magnification side.

Fourth lens element L4has a positive meniscus shape and its convex surface faces the reduction side. Fifth lens element L5has a biconvex shape. Sixth lens element L6has a biconcave shape. Fifth lens element L5and sixth lens element L6are bonded to each other. Seventh lens element L7has a biconvex shape.

Eighth lens element L8has a biconvex shape. Ninth lens element L9has a biconcave shape. Eighth lens element L8and ninth lens element L9are bonded to each other. Tenth lens element L10has a biconvex shape. Eleventh lens element L11has a positive meniscus shape, and its convex surface faces the magnification side.

Relay optical system52includes twelfth to twenty-second lens elements L12to L22, and has a positive power. Twelfth lens element L12has a positive meniscus shape, and its convex surface faces the reduction side. Thirteenth lens element L13has a biconcave shape. Twelfth lens element L12and thirteenth lens element L13are bonded to each other. Fourteenth lens element L14has a positive meniscus shape, and its convex surface faces the reduction side. Fifteenth lens element L15has a negative meniscus shape, and its convex surface faces the magnification side. Sixteenth lens element L16has a biconvex shape. Diaphragm A is disposed between sixteenth lens element L16and seventeenth lens element L17.

Seventeenth lens element L17has a negative meniscus shape, and its convex surface faces the magnification side. Eighteenth lens element L18has a biconvex shape. Nineteenth lens element L19has a biconcave shape. Twentieth lens element L20has a biconvex shape. Nineteenth lens element L19and twentieth lens element L20are bonded to each other. Twenty-first lens element L21has a negative meniscus shape, and its convex surface faces the reduction side. Twenty-second lens element L22has a biconvex shape.

FIG.15is an optical path diagram illustrating an optical path of a ray in projection lens system PL4according to the fourth example. In the present exemplary embodiment, projection lens system PL4includes intermediate imaging position MI between magnification optical system51and relay optical system52. Projection lens system PL4forms an image at intermediate imaging position MI that is conjugate with a reduction conjugate point on image plane S with relay optical system52on the reduction side interposed between intermediate imaging position MI and the reduction conjugate point. Further, imaging at intermediate imaging position MI of projection lens system PL4is performed such that intermediate imaging position MI is conjugate with a magnification conjugate point located at a projection position of screen4or the like with magnification optical system51on the magnification side interposed between intermediate imaging position MI and the magnification conjugate point.

According to projection optical system PL4of the present exemplary embodiment, as illustrated inFIG.15, an angle between most off-axis principal ray31and axial ray32reaches near a right angle on the magnification side, and thus a wide angle of view of projection image20can be achieved.

FIG.16illustrates sufficiency of conditions (1) to (8) in projection lens system PL4according to the fourth example. The table illustrated inFIG.16shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L22in projection lens system PL4of the fourth example, as in the first exemplary embodiment. Projection lens system PL4of the fourth example can also improve the image quality when the brightness is increased.

2. Fifth Example

Projection lens system PL5of a fifth example will be described with reference toFIGS.17to20.

FIG.17is a lens arrangement diagram of projection lens system PL5according to the fifth example.FIG.18is an aberration diagram illustrating longitudinal aberrations of projection lens system PL5.FIGS.17,18illustrate the arrangement of various lenses and various aberrations, respectively in a focused state where the projection distance of projection lens system PL5according to the fifth example is 4,000 mm. A fifth numerical example corresponding to projection lens system PL5of the fifth example will be described later.

FIG.19illustrates an optical path of a ray in projection lens system PL5according to the fifth example. Projection lens system PL5of the fifth example includes magnification optical system51closer to the magnification side than intermediate imaging position MI is, and relay optical system52closer to the reduction side than intermediate imaging position MI is, as in the fourth example.

In the fifth example, magnification optical system51includes first to eleventh lens elements L1to L11, and has a positive power. First lens element L1has a negative meniscus shape, and its convex surface faces the magnification side. Second lens element L2has a negative meniscus shape, and its convex surface faces the magnification side. First lens element L1and second lens element L2are bonded to each other. Third lens element L3has a negative meniscus shape, and its convex surface faces the magnification side.

Fourth lens element L4has a positive meniscus shape, and its convex surface faces the reduction side. Fifth lens element L5has a biconvex shape. Sixth lens element L6has a biconcave shape. Fifth lens element L5and sixth lens element L6are bonded to each other. Seventh lens element L7has a biconvex shape.

Eighth lens element L8has a biconvex shape. Ninth lens element L9has a biconcave shape. Eighth lens element L8and ninth lens element L9are bonded to each other. Tenth lens element L10has a biconvex shape. Eleventh lens element L11has a positive meniscus shape, and its convex surface faces the magnification side.

Relay optical system52includes twelfth to twenty-second lens elements L12to L22, and has a positive power. Twelfth lens element L12has a positive meniscus shape, and its convex surface faces the reduction side. Thirteenth lens element L13has a biconcave shape. Twelfth lens element L12and thirteenth lens element L13are bonded to each other. Fourteenth lens element L14has a biconvex shape. Fifteenth lens element L15has a negative meniscus shape, and its convex surface faces the magnification side. Sixteenth lens element L16has a biconvex shape. Diaphragm A is disposed between sixteenth lens element L16and seventeenth lens element L17.

Seventeenth lens element L17has a negative meniscus shape, and its convex surface faces the magnification side. Eighteenth lens element L18has a biconvex shape. Nineteenth lens element L19has a biconcave shape. Twentieth lens element L20has a biconvex shape. Nineteenth lens element L19and twentieth lens element L20are bonded to each other. Twenty-first lens element L21has a negative meniscus shape, and its convex surface faces the reduction side. Twenty-second lens element L22has a biconvex shape.

FIG.20illustrates sufficiency of conditions (1) to (8) in projection lens system PL5according to the fifth example. The table illustrated inFIG.20shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L22in projection lens system PL5of the fifth example, as in the first exemplary embodiment. Projection lens system PL5of the fifth example can also improve the image quality when the brightness is increased.

3. Sixth Example

Projection lens system PL6of a sixth example will be described with reference toFIGS.21to24.

FIG.21is a lens arrangement diagram of projection lens system PL6according to the sixth example.FIG.22is an aberration diagram illustrating longitudinal aberrations of projection lens system PL6.FIGS.21,22illustrate the arrangement of various lenses and various aberrations, respectively in a focused state where the projection distance of projection lens system PL6according to the sixth example is 4,000 mm. A sixth numerical example corresponding to projection lens system PL6of the sixth example will be described later.

FIG.23illustrates an optical path of a ray in projection lens system PL6according to the sixth example. Projection lens system PL6of the sixth example includes magnification optical system51closer to the magnification side than intermediate imaging position MI is, and relay optical system52closer to the reduction side than intermediate imaging position MI is, as in the fourth example.

In the sixth example, magnification optical system51includes first to eleventh lens elements L1to L11, and has a positive power. First lens element L1has a negative meniscus shape, and its convex surface faces the magnification side. Second lens element L2has a negative meniscus shape, and its convex surface faces the magnification side. Third lens element L3has a negative meniscus shape, and its convex surface faces the magnification side.

Fourth lens element L4has a biconvex shape. Fifth lens element L5has a biconvex shape. Sixth lens element L6has a biconcave shape. Fifth lens element L5and sixth lens element L6are bonded to each other. Seventh lens element L7has a biconvex shape.

Eighth lens element L8has a biconvex shape. Ninth lens element L9has a biconcave shape. Tenth lens element L10has a biconvex shape. Eleventh lens element L11has a positive meniscus shape, and its convex surface faces the magnification side.

Relay optical system52includes twelfth to twenty-second lens elements L12to L22, and has a positive power. Twelfth lens element L12has a positive meniscus shape, and its convex surface faces the reduction side. Thirteenth lens element L13has a biconcave shape. Twelfth lens element L12and thirteenth lens element L13are bonded to each other. Fourteenth lens element L14has a positive meniscus shape, and its convex surface faces the reduction side. Fifteenth lens element L15has a negative meniscus shape, and its convex surface faces the magnification side. Sixteenth lens element L16has a biconvex shape. Diaphragm A is disposed between sixteenth lens element L16and seventeenth lens element L17.

Seventeenth lens element L17has a negative meniscus shape, and its convex surface faces the magnification side. Eighteenth lens element L18has a biconvex shape. Nineteenth lens element L19has a biconcave shape. Twentieth lens element L20has a biconvex shape. Nineteenth lens element L19, twentieth lens element L20, and twenty-first lens element L21are bonded to each other. Twenty-first lens element L21has a negative meniscus shape, and its convex surface faces the reduction side. Twenty-second lens element L22has a biconvex shape.

FIG.24illustrates sufficiency of conditions (1) to (8) in projection lens system PL6according to the sixth example. The table illustrated inFIG.20shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L22in projection lens system PL6of the sixth example, as in the first exemplary embodiment. Projection lens system PL6of the sixth example can also improve the image quality when the brightness is increased.

4. About Fourth to Sixth Examples

Projection lens systems PL4to PL6of the fourth to sixth examples described above include magnification optical system51and relay optical system52so as to have intermediate imaging position MI where imaging is performed inside the projection lens systems. In the present exemplary embodiment, projection lens systems PL4to PL6satisfy following condition (10).

Condition (10) is expressed by the following inequality.
8<|fr/f|<12  (10)

Here, fr indicates the focal length closer to the reduction side than diaphragm A is. f indicates the focal length of the whole system.

Specifically, fr/f=10.08 is satisfied in projection lens system PL4of the fourth example. In projection lens system PL5of the fifth example, fr/f=9.28 is satisfied. In projection lens system PL6of the sixth example, fr/f=10.23 is satisfied.

According to condition (10), the performance of projection lens systems PL4to PL6each having intermediate imaging position MI can be successfully achieved. If the ratio exceeds the upper limit value of condition (10), it becomes difficult to maintain the telecentricity on the reduction side while keeping a long back focus. If the ratio is less than the lower limit value of condition (10), it becomes difficult to correct the aberration, and the image quality of projection image20may be degraded. Ratio fr/f is preferably larger than 8.5 and less than 11.

Third Exemplary Embodiment

A third exemplary embodiment will be described below with reference to the drawings. While the first exemplary embodiment has described an example in which projection lens system PL is of a negative-lead type, projection lens system PL may be of a positive-lead type. In the positive-lead type, the lens group closest to the magnification side in a zoom lens system has a positive power. The third exemplary embodiment will describe projection lens system PL that constitutes a positive-lead zoom lens system.

Hereinafter, description of configurations and operations similar to those of image projection device1and projection lens system PL according to the first exemplary embodiment will be appropriately omitted, and seventh to ninth examples will be described as examples of projection lens system PL according to the present exemplary embodiment.

1. Seventh Example

Projection lens system PL7according to the seventh example of the present disclosure will be described with reference toFIGS.25to27.

FIG.25is a lens arrangement diagram in various states of projection lens system PL7according to the seventh example.FIGS.25(a),25(b),25(c)are lens arrangement diagrams at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL7, respectively, similarly toFIGS.2(a) to2(c).

Projection lens system PL7of the seventh example includes 16 lens elements L1to L16constituting five lens groups G1to G5. As illustrated inFIG.25(a), first to fifth groups G1to G5are arranged in order from the magnification side to the reduction side of projection lens system PL7. In the present exemplary embodiment, projection lens system PL7functions as a zoom lens system by moving each of first to fifth lens groups G1to G5along an optical axis during zooming, as in the first exemplary embodiment.

In projection lens system PL7, first to sixteenth lens elements L1to L16are arranged in order from the magnification side to the reduction side, as in the first exemplary embodiment.FIGS.25(a) to25(c)illustrate back glasses L17to L19as an example of transmission optical system12.

In the projection lens system PL7of the seventh example, first lens group G1includes first and second lens elements L1, L2, and has a positive power. First lens element L1has a negative meniscus shape, and its convex surface faces the magnification side. Second lens element L2has a biconvex shape. First lens element L1and second lens element L2are bonded to each other.

Second lens group G2includes third to fifth lens elements L3to L5, and has a negative power. Third lens element L3has a negative meniscus shape, and its convex surface faces the magnification side. Fourth lens element L4has a negative meniscus shape, and its convex surface faces the magnification side. Fifth lens element L5has a positive meniscus shape, and its convex surface faces the magnification side. Fourth lens element L4and fifth lens element L5are bonded to each other.

Third lens group G3includes sixth lens element L6, and has a negative power. Sixth lens element L6has a biconcave shape.

Fourth lens group G4includes seventh to fourteenth lens elements L7to L14, and has a positive power. Diaphragm A is disposed on the magnification side of seventh lens element L7. Seventh lens element L7has a biconvex shape. Eighth lens element L8has a negative meniscus shape, and its convex surface faces the reduction side. Ninth lens element L9has a biconvex shape. Tenth lens element L10has a biconvex shape. Eleventh lens element L11has a biconcave shape. Twelfth lens element L12has a biconvex shape. Thirteenth lens element L13has a negative meniscus shape, and its convex surface faces the reduction side. Fourteenth lens element L14has a biconvex shape.

Fifth lens group G5includes fifteenth and sixteenth lens elements L15, L16, and has a positive power. Fifteenth lens element L15has a negative meniscus shape, and its convex surface faces the magnification side. Sixteenth lens element L16has a positive meniscus shape, and its convex surface faces the magnification side.

FIG.26is an aberration diagram illustrating longitudinal aberrations of projection lens system PL7according to the seventh example.FIGS.26(a),26(b),26(c) illustrate aberrations at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL7, respectively, similarly toFIGS.3(a) to3(c). The aberrations illustrated inFIGS.26(a) to26(c)are based on a seventh numerical example to be described later.

FIG.27illustrates sufficiency of conditions (1) to (8) in projection lens system PL7according to the seventh example. The table illustrated inFIG.27shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L16in projection lens system PL7of the seventh example, as in the first exemplary embodiment. Projection lens system PL7of the seventh example can also improve the image quality when the brightness is increased.

2. Eighth Example

Projection lens system PL8of an eighth example will be described with reference toFIGS.28to30.

FIG.28is a lens arrangement diagram in various states of projection lens system PL8according to the eighth example.FIGS.28(a),28(b),28(c)are lens arrangement diagrams at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL8, respectively, similarly toFIGS.2(a) to2(c).

Projection lens system PL8of the eighth example includes four lens groups G1to G4to constitute a zoom lens system, as in the seventh example. Projection lens system PL8of the eighth example includes 17 lens elements L1to L17. In projection lens system PL8, first to fourth lens groups G1to G4and first to seventeenth lens elements L1to L17are arranged in order from the magnification side to the reduction side, as in the seventh example.FIGS.28(a) to28(c)illustrate back glasses L18to L20as an example of transmission optical system12.

In projection lens system PL8of the eighth example, first lens group G1includes first and second lens elements L1, L2, and has a positive power. First lens element L1has a negative meniscus shape, and its convex surface faces the magnification side. Second lens element L2has a positive meniscus shape, and its convex surface faces the magnification side.

Second lens group G2includes third to fifth lens elements L3to L5, and has a negative power. Third lens element L3has a negative meniscus shape, and its convex surface faces the magnification side. Fourth lens element L4has a biconcave shape. Fifth lens element L5has a biconcave shape. Sixth lens element L6has a biconvex shape.

Third lens group G3includes seventh to twelfth lens elements L7to L12, and has a positive power. Seventh lens element L7has a biconcave shape. Eighth lens element L8has a biconvex shape. Diaphragm A is disposed between eighth lens element L8and ninth lens element L9. Ninth lens element L9has a negative meniscus shape, and its convex surface faces the reduction side. Tenth lens element L10has a positive meniscus shape, and its convex surface faces the reduction side. Eleventh lens element L11has a biconvex shape. Twelfth lens element L12has a negative meniscus shape, and its convex surface faces the reduction side.

Fourth lens group G4includes thirteenth to seventeenth lens elements L13to L17, and has a positive power. Thirteenth lens element L13has a biconvex shape. Fourteenth lens element L14has a biconcave shape. Thirteenth lens element L13and fourteenth lens element L14are bonded to each other. Fifteenth lens element L15has a biconvex shape. Sixteenth lens element L16has a negative meniscus shape, and its convex surface faces the reduction side. Seventeenth lens element L17has a biconvex shape.

FIG.29is an aberration diagram illustrating longitudinal aberrations of projection lens system PL8according to the eighth example.FIGS.29(a),29(b),29(c)illustrate aberrations at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL8, respectively, similarly toFIGS.3(a) to3(c). The aberrations illustrated inFIGS.29(a) to29(c)are based on an eighth numerical example to be described later.

FIG.30illustrates sufficiency of conditions (1) to (8) in projection lens system PL8according to the eighth example. The table illustrated inFIG.30shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L17in projection lens system PL8of the eighth example, as in the first exemplary embodiment. Projection lens system PL8of the eighth example can also improve the image quality when the brightness is increased.

3. Ninth Example

Projection lens system PL9of a ninth example will be described with reference toFIGS.31to33.

FIG.31is a lens arrangement diagram in various states of projection lens system PL9according to the ninth example.FIGS.31(a),31(b),31(c)are lens arrangement diagrams at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL9, respectively, similarly toFIGS.2(a) to2(c).

Projection lens system PL9of the ninth example includes three lens groups G1to G3to constitute a zoom lens system, as in the seventh example. Projection lens system PL9of the ninth example includes 19 lens elements L1to L19. In projection lens system PL9, first to third lens groups G1to G3and first to nineteenth lens elements L1to L19are arranged in order from the magnification side to the reduction side, as in the seventh example.FIGS.28(a) to28(c)illustrate back glasses L20to L22as an example of transmission optical system12.

In projection lens system PL9of the ninth example, first lens group G1includes first to fourth lens elements L1to L4, and has a positive power. First lens element L1has a biconvex shape. Second lens element L2has a positive meniscus shape, and its convex surface faces the magnification side. Third lens element L3has a biconcave shape. Fourth lens element L4has a positive meniscus shape, and its convex surface faces the magnification side. Third lens element L3and fourth lens element L4are bonded to each other.

Second lens group G2includes fifth to ninth lens elements L5to L9, and has a negative power. Fifth lens element L5has a positive meniscus shape, and its convex surface faces the magnification side. Sixth lens element L6has a negative meniscus shape, and its convex surface faces the magnification side. Seventh lens element L7has a biconcave shape. Eighth lens element L8has a biconcave shape. Ninth lens element L9has a positive meniscus shape, and its convex surface faces the magnification side.

Third lens group G3includes tenth to nineteenth lens elements L10to L19, and has a positive power. Diaphragm A is disposed on the magnification side of tenth lens element L10. Tenth lens element L10has a biconvex shape. Eleventh lens element L11has a negative meniscus shape, and its convex surface faces the reduction side. Twelfth lens element L12has a biconvex shape. Thirteenth lens element L13has a biconcave shape. Fourteenth lens element L14has a biconvex shape. Thirteenth lens element L13and fourteenth lens element L14are bonded to each other.

Fifteenth lens element L15has a negative meniscus shape, and its convex surface faces the magnification side. Sixteenth lens element L16has a biconcave shape. Seventeenth lens element L17has a positive meniscus shape, and its convex surface faces the reduction side. Eighteenth lens element L18has a biconvex shape. Nineteenth lens element L19has a biconvex shape.

FIG.32is an aberration diagram illustrating longitudinal aberrations of projection lens system PL9according to the ninth example.FIGS.32(a),32(b),32(c)illustrate aberrations at the wide-angle end, the intermediate position, and the telephoto end of projection lens system PL9, respectively, similarly toFIGS.3(a) to3(c). The aberrations illustrated inFIGS.32(a) to32(c)are based on a ninth numerical example to be described later.

FIG.33illustrates sufficiency of conditions (1) to (8) in projection lens system PL9according to the ninth example. The table illustrated inFIG.33shows a correspondence between each of conditions (1) to (8) and each of lens elements L1to L19in projection lens system PL5of the fifth example, as in the first exemplary embodiment. For example, projection lens system PL9of the ninth example includes fourteenth lens element L14that satisfies condition (1) but does not satisfy condition (4). Projection lens system PL9of the ninth example can also improve the image quality when the brightness is increased.

4. About Seventh to Ninth Examples

Projection lens systems PL7to PL9of the seventh to ninth examples described above constitute a positive-lead zoom lens system in which lens group G1closest to the magnification side has a positive power. In the present exemplary embodiment, projection lens systems PL7to PL9satisfy following condition (11).

Condition (11) is expressed by the following inequality.
0.5<fr/ft<2.0  (11)

Here, fr indicates a combined focal length of all lenses closer to the reduction side than diaphragm A is in projection lens system PL9. Focal length fr is measured at the telephoto end, for example. Condition (11) defines ratio fr/ft of focal length fr to focal length ft at the telephoto end of the whole system.

Specifically, fr/ft=0.83 is satisfied in projection lens system PL7of the seventh example. In projection lens system PL8of the eighth example, fr/ft=1.73 is satisfied. In projection lens system PL9of the ninth example, fr/ft=0.63 is satisfied.

According to condition (11), the performance of projection lens systems PL7to PL9constituting the positive-lead type zoom lens system can be successfully achieved. If the ratio exceeds the upper limit value of condition (11), it becomes difficult to maintain the telecentricity on the reduction side while keeping a long back focus. If the ratio is less than the lower limit value of condition (11), it becomes difficult to correct the aberration, and the image quality of projection image20may be degraded. Ratio fr/ft is preferably larger than 0.6 and less than 1.8.

Numerical Example

The first to ninth numerical examples for the first to ninth examples of projection lens systems PL1to PL9described above will be shown below.

1. First Numerical Example

The first numerical example corresponding to projection lens system PL1of the first example will be shown below. In the first numerical example, Table 1-1 shows surface data, Table 1-2 shows various data, Table 1-3 shows single lens data, Table 1-4 shows zoom lens group data, and Table 1-5 shows zoom lens group magnification.

TABLE 1-5GROUPFIRSTWIDE-GROUPSURFACEANGLEINTERMEDIATETELEPHOTO110.022880.022880.02288216−2.28121−3.60026−15.982403220.125330.092420.02444
2. Second Numerical Example

The second numerical example corresponding to projection lens system PL2of the second example will be shown below. In the second numerical example, Table 2-1 shows surface data, Table 2-2 shows various data, Table 2-3 shows single lens data, Table 2-4 shows zoom lens group data, and Table 2-5 shows zoom lens group magnification.

TABLE 2-5GROUPFIRSTWIDE-GROUPSURFACEANGLEINTERMEDIATETELEPHOTO110.025090.025090.02509214−1.76128−2.39032−4.334113180.131650.111770.07111
3. Third Numerical Example

The third numerical example corresponding to projection lens system PL3of the third example will be shown below. In the third numerical example, Table 3-1 shows surface data, Table 3-2 shows various data, Table 3-3 shows single lens data. Table 3-4 shows zoom lens group data, and Table 3-5 shows zoom lens group magnification.

The fourth numerical example corresponding to projection lens system PL4of the fourth example will be shown below. In the fourth numerical example, Table 4-1 shows surface data, Table 4-2 shows various data, and Table 4-3 shows single lens data.

The fifth numerical example corresponding to projection lens system PL5of the fifth example will be shown below. In the fifth numerical example, Table 5-1 shows surface data, Table 5-2 shows various data, and Table 5-3 shows single lens data.

The sixth numerical example corresponding to projection lens system PL6of the sixth example will be shown below. In the sixth numerical example, Table 6-1 shows surface data, Table 6-2 shows various data, and Table 6-3 shows single lens data.

The seventh numerical example corresponding to projection lens system PL7of the seventh example will be shown below. In the seventh numerical example, Table 7-1 shows surface data, Table 7-2 shows various data, Table 7-3 shows single lens data, Table 7-4 shows zoom lens group data, and Table 7-5 shows zoom lens group magnification.

The eighth numerical example corresponding to projection lens system PL8of the eighth example will be shown below. In the eighth numerical example, Table 8-1 shows surface data, Table 8-2 shows various data, Table 8-3 shows single lens data, Table 8-4 shows zoom lens group data, and Table 8-5 shows zoom lens group magnification.

TABLE 8-5GROUPFIRSTWIDE-GROUPSURFACEANGLEINTERMEDIATETELEPHOTO11−0.03991−0.03991−0.0399125−0.41263−0.45265−0.48951313−0.77026−0.87747−1.020954260.442830.433730.42331
9. Ninth Numerical Example

The ninth numerical example corresponding to projection lens system PL9of the ninth example will be shown below. In the ninth numerical example, Table 9-1 shows surface data, Table 9-2 shows various data, Table 9-3 shows single lens data, Table 9-4 shows zoom lens group data, and Table 9-5 shows zoom lens group magnification.

The exemplary embodiments have been described above as examples of the technique in the present disclosure. For that purpose, the accompanying drawings and the detailed description have been provided.

The constituent elements illustrated in the accompanying drawings and described in the detailed description may include constituent elements essential for solving the problems, as well as constituent elements that are not essential for solving the problems but required to exemplify the above technique. Therefore, it should not be immediately assumed that the unessential constituent elements are essential constituent elements due to the fact that the unessential constituent elements are described in the accompanying drawings and the detailed description.

Note that the exemplary embodiments described above are provided to exemplify the technique in the present disclosure. Therefore, it is possible to make various changes, replacements, additions, omissions, and the like within the scope of the claims and equivalents thereof.

Summary of Aspects

Hereinafter, various aspects according to the present disclosure will be exemplified.

A first aspect according to the present disclosure is a projection lens system that projects an image of a reduction side into a magnification side in an image projection device, a back glass being disposed on the reduction side. The projection lens system includes one or more negative lenses that have a surface on the reduction side and a surface on the magnification side and that satisfy following condition (1) in the surface on the reduction side or the surface on the magnification side. All of the one or more negative lenses satisfying condition (1) satisfy following conditions (2) and (3),
|h/H|<2.0  (1)
Tn≥98.5%  (2)
Dn/Db≤0.05  (3)

where

h indicates a height of a most off-axis principal ray,

H indicates a height of an axial ray passing through a highest pupil position,

Tn indicates a transmittance of light having a wavelength of 460 nm when a lens material of the one or more negative lenses has a thickness of 10 mm,

Dn indicates a thickness of the one or more negative lenses on an optical axis, and

Db indicates a total thickness of the back glass.

According to the projection lens system described above, under condition (1), all of the negative lenses that are assumed to be easily affected by heat when the brightness of the image projection device is increased and are assumed to easily affect the performance of the projection lens system satisfy conditions (2) and (3) for reducing the influence of heat. As a result, it is possible to reduce a variation in a projection image due to high brightness of the image projection device and improve the image quality.

According to a second aspect, in the projection lens system of the first aspect, all of the one or more negative lenses satisfying condition (1) further satisfy following condition (4),
|fn/fw|>1.2  (4)

where

fn indicates a focal length of the one or more negative lenses, and

fw indicates a focal length at a wide-angle end of a whole system.

According to the projection lens system described above, by weakening the power of the negative lens that is easily affected by heat in advance under condition (4), it is possible to stabilize the variation in the projection image when the brightness is increased.

According to a third aspect, in the projection lens system of the first aspect, at least one of the one or more negative lenses satisfies following condition (5),
vn<40  (5)

where

vn indicates an Abbe number of a lens material of at least one of the one or more negative lenses.

According to the projection lens system described above, by setting the Abbe number of at least one of all negative lenses to be less than the upper limit value of condition (5), it is possible to successfully correct chromatic aberrations while reducing the influence of heat when the brightness is increased. Consequently, it is possible to improve the image quality of the projection image when the brightness is increased.

According to a fourth aspect, the projection lens system of the first aspect constitutes a substantially telecentric system on the reduction side. Consequently, it is possible to reduce a color shift in the back lens on the reduction side and the like.

According to a fifth aspect, the projection lens system of the first aspect includes a diaphragm and one or more positive lenses disposed closer to the reduction side than the diaphragm is. All of the one or more negative lenses are disposed closer to the reduction side than the diaphragm is, and all of the one or more positive lenses satisfy condition (1). As a result, the projection lens system can be downsized.

According to a sixth aspect, the projection lens system of the first aspect further includes one or more positive lenses that satisfy condition (1). All of the one or more positive lenses satisfying condition (1) satisfy following condition (6),
Tp>98.5%  (6)

where

Tp indicates a transmittance of light having a wavelength of 460 nm when a lens material of the one or more positive lenses has a thickness of 10 mm. As a result, it is possible to reduce the influence of heat on the positive lens and improve the image quality of the projection image.

According to a seventh aspect, the projection lens system of the first aspect includes at least 15 lenses. According to the projection lens system described above, it is possible to successfully correct various aberrations in the projection lens system.

According to an eighth aspect, the projection lens system of the first aspect further includes four positive lenses that satisfy condition (1). The four positive lenses satisfying condition (1) satisfy following condition (7),
dn/dt<−4.5×10−6(7)

where

dn/dt indicates a temperature coefficient of a relative refractive index of a lens material of the four positive lenses at room temperature.

As a result, it is possible to reduce the influence of heat on the positive lens and improve the image quality of the projection image.

According to a ninth aspect, the projection lens system of the first aspect further includes a positive lens that satisfies condition (1). The positive lens satisfying condition (1) satisfies following condition (8),
vp<40  (8)

where

vp indicates an Abbe number of a lens material of the positive lens.

As a result, it is possible to reduce the influence of heat on the positive lens and improve the image quality of the projection image.

According to a tenth aspect, the projection lens system of the first aspect further includes a diaphragm. The projection lens system constitutes a zoom lens system including a plurality of lens groups. In the lens groups, a lens group closest to the magnification side has a negative power. The projection lens system satisfies following condition (9),
2<fr/fw<4.5  (9)

where

fr indicates a focal length at a wide-angle end closer to the reduction side than the diaphragm is, and

fw indicates a focal length at the wide-angle end of a whole system.

The projection lens system described above can improve the image quality of the projection image as a negative-lead zoom lens system.

According to an eleventh aspect, the projection lens system of the first aspect further includes a diaphragm. The projection lens system has an intermediate imaging position where an image is formed inside the projection lens system. In the projection lens system, a magnification optical system constituted by a plurality of lenses disposed closer to the magnification side than the intermediate imaging position is has a positive power. A relay optical system constituted by a plurality of lenses disposed closer to the reduction side than the intermediate imaging position is has a positive power. The projection lens system satisfies following condition (10),
8<|fr/f|<12  (10)

where

fr indicates a focal length closer to the reduction side than the diaphragm is, and

f indicates a focal length of a whole system.

According to the projection lens system described above, it is possible to improve the image quality of the projection image in a lens system using the intermediate imaging position.

According to a twelfth aspect, the projection lens system of the first aspect further includes a diaphragm. The projection lens system constitutes a zoom lens system including a plurality of lens groups. In the lens groups, a lens group closest to the magnification side has a positive power. The projection lens system satisfies following condition (11),
0.5<fr/ft<2.0  (11)

where

fr indicates a focal length closer to the reduction side than the diaphragm is, and

ft indicates a focal length at a telephoto end of a whole system.

The projection lens system described above can improve the image quality of the projection image as a positive-lead zoom lens system.

A thirteenth aspect is an image projection device including the projection lens system of the first aspect and an image forming element that forms an image. The image projection device described above can improve the image quality of an image when the brightness is increased.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, an image projection device having a light output of 20,000 lumens or more, and a projection lens system mounted on the image projection device.

REFERENCE MARKS IN THE DRAWINGS