Multifocal lens, projector, and imaging apparatus

Abstract

To further reduce the size of a multifocal lens.SOLUTION: A multifocal lens 40 is composed of a plurality of lens groups 41, 42, 43, 44, and 45, and has a focal position changed by changing positions of the lens groups 41, 42, 43, 44, and 45. For magnification chromatic aberration characteristics of the multifocal lens 40, a larger one of an aberration amount at a wide angle end and an aberration amount at a telephoto end is smaller than an aberration amount in an intermediate region between the wide angle end and the telephoto end.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a bifocal lens capable of operating at a plurality of focal lengths, a projector equipped with the bifocal lens, and an imaging device equipped with the bifocal lens. [Background technology]

[0002] A known projection-type variable-focus lens for projectors has a first lens group including one or two lenses, a second lens group including two lenses, and a third lens group including three lenses, in which the first lens group is fixed and the second lens group and the third lens group move independently when changing magnification (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-53507 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned projection type variable focus lens achieves relatively good aberration characteristics at the wide-angle end, intermediate position and telephoto end, but the overall lens length is long compared to the image height, and the overall lens length is large compared to the size of the image display surface. [Means for solving the problem]

[0005] A bifocal lens in one aspect of the present invention is a bifocal lens composed of a plurality of lens groups, in which the focal position changes by changing the position of the lens groups, and in which, regarding the lateral chromatic aberration characteristics of the bifocal lens, the larger of the aberration amounts at the wide-angle end and the telephoto end is smaller than the aberration amount in an intermediate region between the wide-angle end and the telephoto end.

[0006] A projector in one aspect of the present invention comprises the above-mentioned bifocal lens and an image forming unit that forms a projected image on the reduction side conjugate plane of the bifocal lens, and the image forming unit has a light source device and a light modulation element that modulates light from the light source device.

[0007] An imaging device according to one aspect of the present invention includes the bifocal lens described above, and an imaging element disposed on a reduction-side conjugate plane of the bifocal lens. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a projector including a bifocal lens according to a first embodiment. [Diagram 2] 1 is a configuration and light ray diagram of a bifocal lens of a first embodiment. [Diagram 3] 1 is a diagram showing the configuration of a bifocal lens according to a first embodiment. [Figure 4] 4A to 4C are diagrams illustrating the magnification changing operation of the bifocal lens of the first embodiment. [Diagram 5] 4 shows the lateral chromatic aberration characteristics of the bifocal lens of Example 1. [Figure 6] 3 shows the longitudinal aberration characteristics of the bifocal lens of Example 1. [Figure 7] FIG. 11 is a diagram showing the configuration of a bifocal lens according to a second embodiment. [Figure 8] 11A to 11C are diagrams illustrating the magnification changing operation of the bifocal lens of the second embodiment. [Figure 9] 4 shows the lateral chromatic aberration characteristics of the bifocal lens of Example 2. [Figure 10] 4 shows the longitudinal aberration characteristics of the bifocal lens of Example 2. [Figure 11] FIG. 11 is a diagram showing the configuration of a bifocal lens according to a third embodiment. [Figure 12] 13A to 13C are diagrams illustrating the magnification changing operation of the bifocal lens of the third embodiment. [Figure 13] 4 shows the lateral chromatic aberration characteristics of the bifocal lens of Example 3. [Figure 14] 13 shows the longitudinal aberration characteristics of the bifocal lens of Example 3. [Figure 15]11A and 11B are diagrams illustrating an imaging device including a bifocal lens according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [First embodiment] A bifocal lens according to a first embodiment of the present invention and a projector incorporating the same will be described below with reference to the drawings.

[0010] As shown in FIG. 1, a projector 2 incorporating a bifocal lens 40 according to the first embodiment includes an optical system portion 50 that projects image light, and a circuit device 80 that controls the operation of the optical system portion 50.

[0011] In the optical system section 50, the light source device 10 emits light including R light, G light, and B light in a homogenized state. The light source device 10 has a light source lamp such as extra-high pressure mercury, a two-stage integrator lens having a plurality of lens elements arranged in an array, a polarization conversion element that converts the light that has passed through the two-stage integrator lens into a predetermined linearly polarized light, and a superimposing lens that superimposes the illumination light emitted from the latter stage integrator lens on the display area of ​​the liquid crystal panels 29R, 29G, and 29B.

[0012] The first dichroic mirror 21 reflects the R light incident from the light source device 10 and transmits the G and B lights. The R light reflected by the first dichroic mirror 21 passes through a reflecting mirror 25 and a field lens 28R and enters a liquid crystal panel 29R, which is a light modulation element OM. The liquid crystal panel 29R forms an R-color image by modulating the R light in accordance with an image signal.

[0013] The second dichroic mirror 22 reflects the G light from the first dichroic mirror 21 and transmits the B light. The G light reflected by the second dichroic mirror 22 passes through a field lens 28G and enters a liquid crystal panel 29G, which is a light modulation element OM. The liquid crystal panel 29G forms a G color image by modulating the G light according to an image signal. The B light transmitted through the second dichroic mirror 22 passes through relay lenses 23 and 24, reflecting mirrors 26 and 27, and a field lens 28B and enters a liquid crystal panel 29B, which is a light modulation element OM. The liquid crystal panel 29B forms a B color image by modulating the B light according to an image signal.

[0014] The cross dichroic prism 31 is a prism for light synthesis, which synthesizes the lights modulated by the liquid crystal panels 29R, 29G, and 29B to form image light, and causes the image light to proceed to the bifocal lens 40.

[0015] The bifocal lens 40 is a projection lens that enlarges and projects the image light modulated by each of the liquid crystal panels 29R, 29G, and 29B and combined by the cross dichroic prism 31 onto a screen (not shown). The liquid crystal panels 29R, 29G, and 29B are an image forming unit 20a that forms a projection image on a reduction-side conjugate plane RC (see FIG. 2, which will be described later) of the bifocal lens 40.

[0016] The circuit device 80 includes an image processing unit 81 to which an external image signal such as a video signal is input, a display driving unit 82 that drives liquid crystal panels 29R, 29G, and 29B provided in the optical system portion 50 based on the output of the image processing unit 81, a lens driving unit 83 that operates a driving mechanism (not shown) provided in the bifocal lens 40 to adjust the state of the bifocal lens 40, and a main control unit 88 that comprehensively controls the operation of these circuit portions 81, 82, 83, etc.

[0017] The image processing unit 81 converts the input external image signal into an image signal including color gradations, etc. The image processing unit 81 can also perform various types of image processing, such as distortion correction and color correction, on the external image signal.

[0018] The display drive unit 82 can operate the liquid crystal panels 29R, 29G, and 29B based on the image signal output from the image processing unit 81, and can form, on the liquid crystal panels 29R, 29G, and 29B, an image corresponding to the image signal or an image obtained by subjecting the image signal to image processing.

[0019] The lens driver 83 operates under the control of the main controller 88, and can change the state of the bifocal lens 40 between the wide-angle end and the telephoto end by appropriately moving some of the optical elements constituting the bifocal lens 40 along the optical axis OA via the actuator AC. At this time, the lens groups to be moved can be moved individually, or they can be linked together using a cam mechanism. In this way, when the magnification is changed electrically using the actuator AC, the bifocal lens 40 can be smoothly switched between the wide-angle end and the telephoto end in a binary manner, reducing the stress on the user.

[0020] The actuator AC and the like may be omitted. In other words, some of the optical elements constituting the bifocal lens 40 may be manually moved using a mechanical mechanism including a cam mechanism or the like to switch the state of the bifocal lens 40 between the wide-angle end and the telephoto end.

[0021] The lens driving unit 83 may automatically adjust the focus state of the bifocal lens 40. The lens driving unit 83 may change the vertical position and projection state of the image projected on the screen by adjusting the tilt that moves the entire bifocal lens 40 in the up and down direction perpendicular to the optical axis OA.

[0022] Hereinafter, the bifocal lens 40 of the embodiment will be specifically described with reference to Fig. 2. The bifocal lens 40 illustrated in Fig. 2 has the same configuration as the bifocal lens 40 of Example 1 described later.

[0023] The bifocal lens 40 of the embodiment projects an image formed on the projection surface of the liquid crystal panel 29G (29R, 29B) onto a screen (not shown). Here, a prism PR corresponding to the cross dichroic prism 31 in FIG. 1 is disposed between the bifocal lens 40 and the liquid crystal panel 29G (29R, 29B).

[0024] The bifocal lens 40 includes, in order from the screen, which is the enlargement side, a first lens group 41 having a negative refractive power, a second lens group 42 having a positive refractive power, a third lens group 43 having a negative refractive power, a fourth lens group 44 having a positive refractive power, and a fifth lens group 45 having a positive refractive power. When the bifocal lens 40 changes magnification, the second lens group 42 to the fourth lens group 44 move from the reduction side to the enlargement side while changing the interval between the adjacent lens groups, when changing magnification to increase the focal length. In other words, the second lens group 42 to the fourth lens group 44 move in a direction away from the liquid crystal panel 29G (29R, 29B) and toward the screen. At that time, the first lens group 41 and the fifth lens group 45 are fixed, and a substantially telecentric state is maintained on the reduction side, that is, on the liquid crystal panel 29G (29R, 29B) side.

[0025] In the bifocal lens 40, the first lens group 41 is made of a plastic negative aspherical lens, and the second lens group 42 is made of a biconvex lens. The third lens group 43 is made of a cemented lens 43u, which is made by cementing a biconcave lens 43a and a positive meniscus lens 43b, from the enlargement side. The fourth lens group 44 is made of a cemented lens 44u and a biconvex lens 44c, which is made by cementing a biconcave lens 44a and a biconvex lens 44b, from the enlargement side. The fifth lens group 45 is made of a plastic positive aspherical lens. The second lens group 42 to the fourth lens group 44 are made of glass.

[0026] The bifocal lens 40 is approximately telecentric on the object side or reduction side where the liquid crystal panels 29G (29R, 29B) are located. This makes it possible to increase the light utilization efficiency and easily absorb variations in assembly when the light modulated by each liquid crystal panel 29G (29R, 29B) is synthesized in the cross dichroic prism 31 to produce image light.

[0027] The bifocal lens 40 has an aperture stop ST between the third lens group 43 and the fourth lens group 44, and moves in accordance with the third lens group 43 or the fourth lens group 44.

[0028] In the multifocal lens 40 of the embodiment, the first lens group 41 has negative refractive power, and the second lens group 42 and subsequent lenses have positive refractive power as a whole, so that it is possible to realize a wide angle and a long back focus while avoiding an increase in the diameter of the first lens group 41. In addition, the second lens group 42 corrects the lateral chromatic aberration caused by the first lens group 41, the negative power of the third lens group 43 corrects the positive lateral chromatic aberration caused by the fourth lens group 44 and the fifth lens group 45, and the fourth lens group 44 and the fifth lens group 45 can ensure that the reduction side is telecentric relative to the fifth lens group 45, thereby realizing good aberration characteristics.

[0029] In the bifocal lens 40 of the embodiment, the first lens group 41 and the fifth lens group 45 are fixed during magnification change, and the second lens group 42, the third lens group 43, and the fourth lens group 44 move from the reduction side to the enlargement side independently of each other during a transition from the wide-angle end to the telephoto end where the focal length is increased, and the second lens group 42, the third lens group 43, and the fourth lens group 44 move in the opposite direction to the above during a transition from the telephoto end to the wide-angle end where the focal length is decreased. During magnification change, the first lens group 41 and the fifth lens group 45 are fixed, and only the second lens group 42 to the fourth lens group 44 move independently of each other, so that the overall length of the bifocal lens 40 does not change, and the structure of the lens barrel that holds the bifocal lens 40 can be simplified.

[0030] In the bifocal lens 40 of the embodiment, the larger of the aberration amounts at the wide-angle end and the telephoto end is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end. In the above, the intermediate region means the state of the bifocal lens 40 in which the focal length becomes the average focal length of the focal length at the wide-angle end and the focal length at the telephoto end when the bifocal lens 40 is changed in magnification. In addition, the aberration amount at the wide-angle end or the telephoto end means the absolute value of the aberration amount is maximum within the range of the target image height. The shortest blue wavelength and the longest red wavelength are considered for the bifocal lens 40. Specifically, the blue wavelength is 470 nm, and the red wavelength is 620 nm. In an optical system that realizes such a bifocal lens 40, the power of each lens group 41, 42, 43, 44, and 45 can be strengthened, so that the movement amount of the lens groups 42, 43, and 44 when realizing multiple foci can be suppressed. As a result, it is possible to maintain performance while suppressing an increase in the overall length of the bifocal lens 40, that is, the lens length, and it is possible to make the bifocal lens 40 more compact.

[0031] In the bifocal lens 40 of the embodiment, the larger of the aberration amounts at the wide-angle end and the telephoto end is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end in terms of the spherical aberration characteristics. In the above, the intermediate region is defined in the same manner as in the case of the magnification chromatic aberration characteristics. Moreover, the aberration amount at the wide-angle end or the telephoto end means the aberration amount whose absolute value is the maximum within the range of the target image height. As in the case of the magnification chromatic aberration characteristics, the shortest blue wavelength and the longest red wavelength are considered for the spherical aberration characteristics. In an optical system that realizes such spherical aberration characteristics, the lens power of each of the lens groups 41, 42, 43, 44, and 45 can be strengthened, so that the bifocal lens 40 can be made more compact. In particular, better aberration characteristics can be obtained at the wide-angle end and the telephoto end. In addition, the bifocal lens 40 of the embodiment has astigmatism characteristics in which the larger of the aberration amounts at the wide-angle end and the telephoto end, for example, the aberration amount at the telephoto end is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end. In an optical system that realizes such astigmatism characteristics, the lens power of each of the lens groups 41, 42, 43, 44, and 45 can be strengthened, so that the bifocal lens 40 can be made more compact. In particular, better aberration characteristics can be obtained at the wide-angle end and the telephoto end.

[0032] In the above, we have focused on the intermediate region between the wide-angle end and the telephoto end, but even in a quasi-intermediate region, such as the wide-angle end side of the intermediate region or the telephoto end side of the intermediate region, it is more desirable that the larger of the aberration amounts at the wide-angle end and the telephoto end, for the magnification chromatic aberration characteristics, spherical aberration characteristics, and astigmatism characteristics, be smaller than the aberration amounts in the quasi-intermediate region.

[0033] In the bifocal lens 40 of the embodiment, the ratio ft / fw of the focal length fw of the entire system at the wide-angle end to the focal length ft of the entire system at the telephoto end is 1.20 or more. Such a bifocal lens 40 is a compact optical system in which the overall length of the bifocal lens 40 is short relative to the image height, while increasing the focal difference between the wide-angle end and the telephoto end.

[0034] The bifocal lens 40 of the embodiment satisfies the following conditional expressions. 1.0≦|fG1 / fG2| … (1) Here, the value fG1 is the focal length of the first lens group 41, and the value fG2 is the focal length of the second lens group 42. In this way, making the power of the second lens group 42 equal to or stronger than that of the first lens group 41, in other words, making the bifocal difference (magnification difference) larger, contributes to shortening the overall length.

[0035] The value |fG1 / fG2| in the above conditional formula (1) is determined from the viewpoint of shortening the overall length. 1.3≦|fG1 / fG2| … (1)' It is preferable that:

[0036] The value |fG1 / fG2| is set to avoid deterioration of various aberrations. 1.0≦|fG1 / fG2|≦1.5 … (1)” It is preferable that:

[0037] The bifocal lens 40 of the embodiment satisfies the following conditional expressions. 0.10≦M4 / LL≦0.35 … (2) Here, the value M4 is the movement amount of the fourth lens group 44 from the wide-angle end to the telephoto end, and the value LL is the lens length. In this way, by relatively increasing the movement amount of the fourth lens group 44, it is possible to contribute to shortening the overall length while increasing the bifocal difference (magnification difference). By setting the value M4 / LL of the above conditional formula to the lower limit or more, it is easy to obtain the bifocal difference (magnification difference). By setting the value M4 / LL of the above conditional formula to the upper limit or less, it is possible to avoid the problem of the overall length becoming large and various aberrations becoming worse. Note that, normally, an aperture stop ST is disposed between the third lens group 43 and the fourth lens group 44, and the large movement amount of the fourth lens group 44 can be considered to be a large movement amount of the part behind the aperture stop ST, that is, the reduction side.

[0038] For the value M4 / LL, 0.20≦M4 / LL≦0.35 … (2)' It is preferable that:

[0039] The bifocal lens 40 of the embodiment satisfies the following conditional expressions. AVνd1 / AVνd2≦0.80 … (3) Here, the value AVνd1 is the average Abbe number for the d-line of the first lens group 41, and the value AVνd2 is the average Abbe number for the d-line of the second lens group 42. In other words, a material with a low Abbe number is used for the second lens group 42. The lateral chromatic aberration (which is relatively large due to a large change in the angle of the light ray) occurring in the first lens group 41 can be effectively corrected by the second lens group 42, which has a large dispersion. This makes it possible to achieve compactness while effectively correcting chromatic aberration. Note that compactness can be achieved more easily if the second lens group 42 is a single lens.

[0040] For the value AVνd1 / AVνd2, AVνd1 / AVνd2≦0.70 … (3)' It is preferable that:

[0041] The bifocal lens 40 of the embodiment satisfies the following conditional expressions. LL / HI≦8.0 … (4) Here, the value LL is the lens length, and the value HI is the image height. By satisfying the above conditional expression (4), it is possible to contribute to making the bifocal lens 40 more compact.

[0042] For the value LL / HI, LL / HI≦6.0 … (4)' It is preferable that:

[0043] As described above, the bifocal lens 40 of the embodiment is composed of multiple lens groups 41, 42, 43, 44, and 45, and is a bifocal lens in which the focal position changes by changing the positions of the lens groups 41, 42, 43, 44, and 45. Regarding the magnification chromatic aberration characteristics of the bifocal lens 40, the larger of the aberration amounts at the wide-angle end and the telephoto end is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end.

[0044] In an optical system that realizes such lateral chromatic aberration characteristics, the lens power of each group can be strengthened, so that the amount of movement of the lens groups 41, 42, 43, 44, and 45 when realizing multiple focal points can be reduced. As a result, the performance can be maintained while suppressing an increase in the overall length of the bifocal lens 40 relative to the image height, i.e., the lens length, and the bifocal lens 40 can be made smaller.

[0045] As described above, the projector 2 of the embodiment includes the bifocal lens 40 and the image forming section 20a that forms a projection image on the reduction-side conjugate plane RC of the bifocal lens 40, and the image forming section 20a includes the light source device 10 and the light modulation element OM that modulates the light from the light source device 10. This makes it possible to reduce the size of the projector 2 that includes the bifocal lens 40.

[0046] [Example] Hereinafter, examples of the bifocal lens 40, which is a projection lens, will be described. The meanings of the specifications common to Examples 1 to 3 described below are summarized below. R radius of curvature D Axis surface spacing (lens thickness or lens spacing) Nd Refractive index of d line Vd Abbe number of d line

[0047] The aspheric surface is specified by the following polynomial (aspheric surface equation): TIFF2025070042000002.tif16166However, c: Curvature (1 / R) h: Height from the optical axis k: conic coefficient of aspheric surface Ai: High-order aspheric coefficients of aspheric surface Note that surface number 0 refers to the image surface (projected surface) on the screen, STO refers to the aperture stop ST, and the final surface number refers to the display surface of the liquid crystal panel 29G, etc. Furthermore, a surface with an "*" after the surface number is an aspheric surface.

[0048] Example 1 The lens surface data for Example 1 is shown in Table 1 below. [Table 1] Surface number RD Nd Vd 0 Infinity 1800.00 1* -22.008 3.8000 1.535038 55.7111 2* -1143.411 15.5639 3 26.549 2.8288 1.834000 37.1611 4 -268.704 1.3578 5 -49.396 1.2000 1.720467 34.7081 6 14.193 2.0000 1.922860 20.8801 7 39.656 3.0000 8(STO) Infinity 8.9987 9 -12.340 1.2000 1.728250 28.4611 10 45.593 5.2020 1.552001 70.6971 11 -14.918 0.1824 12 51.483 4.5087 1.528411 76.4531 13 -28.571 0.5000 14* 46.024 4.6577 1.535038 55.7111 15* -55.733 6.0000 16 Infinity 24.7200 1.516331 64.1421 17 Infinity 5.5034 18 Infinity -0.0300

[0049] Table 2 below shows values ​​of on-axis surface spacing D at variable spacing locations on lens surfaces at the wide-angle end (wide), the middle position (middle), and the telephoto end (tele) for Example 1. [Table 2] Room number wide middle tele 2 15.564 11.993 5.251 4 1.358 4.914 7.450 7 3.000 0.738 1.000 8 8.999 4.237 4.229 13 0.500 8.696 11.490 17 5.503 4.316 5.396

[0050] Table 3 below shows the aspheric coefficients of the lens surfaces in the first embodiment. [Table 3] Aspheric coefficients Surface number RK A4 A6 A8 A10 A12 A14 A16 1 -2.200800E+01 0.000000 3.050208E-04 -2.546031E-06 2.112792E-08 -1.452593E-10 7.436542E-13 -2.353712E-15 3.304510E-18 2 -1.143411E+03 0.000000 2.817394E-04 -2.311550E-06 3.483659E-08 -6.043723E-10 6.986117E-12 -4.227135E-14 1.022278E-16 14 4.602400E+01 -80.000000 9.304468E-05 -1.930132E-06 2.756054E-08 -2.784933E-10 1.682655E-12 -5.554550E-15 7.189776E-18 15 -5.573300E+01 -74.263689 -4.585970E-05 -1.262879E-09 4.270808E-09 -7.120567E-11 5.005330E-13 -1.781539E-15 2.290665E-18 In Table 3 above and the following tables, powers of 10 (e.g., 1.00×10 +18 ) is expressed using E (for example, 1.00E+18).

[0051] Fig. 3 is a cross-sectional view of the bifocal lens 40 of Example 1. The bifocal lens 40 shown in Fig. 3 corresponds to the bifocal lens 40 of the first embodiment. This bifocal lens 40 has a total length, i.e., lens length, of 55 mm, LL / HI ≈ 5.78, and a bifocal difference of 1.50 times.

[0052] The bifocal lens 40 enlarges and projects an image on a display surface such as the liquid crystal panel 29G at a magnification according to the distance to the screen. The bifocal lens 40 includes, in order from the screen on the enlarged side, a first lens group 41 with negative refractive power, a second lens group 42 with positive refractive power, a third lens group 43 with negative refractive power, a fourth lens group 44 with positive refractive power, and a fifth lens group 45 with positive refractive power. A prism PR is disposed between the fifth lens group 45 and the liquid crystal panel 29G.

[0053] As shown in Fig. 4, when the magnification of the bifocal lens 40 is changed, the first lens group 41 and the fifth lens group 45 are fixed, and the second lens group 42 to the fourth lens group 44 move, and the bifocal lens 40 is approximately telecentric on the reduction side. wide The second lens group 42 to the fourth lens group 44 are disposed on the reduction side closer to the liquid crystal panel 29G. tele The second lens group 42 to the fourth lens group 44 move as a whole toward the enlargement side toward the screen while changing the intervals between adjacent lens groups.

[0054] Returning to FIG. 3, the first lens group 41 is made of a plastic negative aspherical lens, and the second lens group 42 is made of a biconvex lens. The third lens group 43 is made of a cemented lens 43u, which is made by cementing a biconcave lens 43a and a positive meniscus lens 43b, from the enlargement side. The fourth lens group 44 is made of a cemented lens 44u and a biconvex lens 44c, which is made by cementing a biconcave lens 44a and a biconvex lens 44b, from the enlargement side. The fifth lens group 45 is made of a plastic positive aspherical lens. The second lens group 42 to the fourth lens group 44 are made of glass.

[0055] Fig. 5 is a diagram showing the lateral chromatic aberration characteristics of the bifocal lens of Example 1. In Fig. 5, region AR1 shows the lateral chromatic aberration characteristics at the wide-angle end (focal length fw = 16.50 mm), region AR2 shows the lateral chromatic aberration characteristics at the intermediate region (focal length fm = 20.63 mm) which is the intermediate position, and region AR3 shows the lateral chromatic aberration characteristics at the telephoto end (focal length ft = 24.75 mm). Regarding the lateral chromatic aberration characteristics of the bifocal lens of Example 1, the larger of the aberration amounts at the wide-angle end and the telephoto end, that is, the aberration amount at the wide-angle end, is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end.

[0056] Fig. 6 is a diagram showing the longitudinal aberration characteristics (i.e., spherical aberration characteristics, astigmatism characteristics, and distortion aberration characteristics) of the bifocal lens of Example 1. In Fig. 6, region BR1 shows the longitudinal aberration at the wide-angle end (focal length fw = 16.50 mm), region BR2 shows the longitudinal aberration in the intermediate region (focal length fm = 20.63 mm) which is the intermediate position, and region BR3 shows the longitudinal aberration at the telephoto end (focal length ft = 24.75 mm). Regarding the spherical aberration characteristics of the bifocal lens of Example 1, the larger of the aberration amount at the wide-angle end and the aberration amount at the telephoto end, that is, the aberration amount at the telephoto end, is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end. Regarding the astigmatism characteristics of the bifocal lens of Example 1, the larger of the aberration amounts at the wide-angle end and the telephoto end, that is, the aberration amount at the telephoto end, is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end.

[0057] Example 2 The lens surface data for Example 2 is shown in Table 4 below. [Table 4] Surface number RD Nd Vd 0 Infinity 1800.00 1* -18.362 3.8000 1.535038 55.7111 2* -102.328 15.0698 3 41.739 2.8288 1.834000 37.1611 4 -87.656 1.7576 5 -44.575 1.2000 1.720467 34.7081 6 16.357 2.0000 1.922860 20.8801 7 96.873 3.0000 8(STO) Infinity 8.5258 9 -11.054 1.2000 1.728250 28.4611 10 49.176 5.2020 1.552001 70.6971 11 -14.688 0.1824 12 100.294 4.5087 1.528411 76.4531 13 -21.488 1.0673 14* 46.045 4.6577 1.535038 55.7111 15* -53.528 6.0000 16 Infinity 24.7200 1.516331 64.1421 17 Infinity 4.5331 18 Infinity -0.0183

[0058] Table 5 below shows values ​​of on-axis surface spacing D at variable spacing locations on lens surfaces at the wide-angle end (wide), the middle position (middle), and the telephoto end (tele) for Example 2. [Table 5] Room number wide middle tele 2 15.070 7.561 6.041 4 1.758 5.103 7.045 7 3.000 5.006 1.000 8 8.526 7.203 4.796 13 1.067 5.922 10.539 17 4.533 4.903 4.435

[0059] Table 6 below lists the aspheric coefficients of the lens surfaces in Example 2. [Table 6] Aspheric coefficients Surface number RK A4 A6 A8 A10 A12 A14 A16 1 -18.362 0.000000 3.167599E-04 -2.595590E-06 2.136227E-08 -1.441726E-10 7.408873E-13 -2.399098E-15 3.486879E-18 2 -102.328 0.000000 2.705639E-04 -2.400840E-06 3.534280E-08 -6.043636E-10 6.953034E-12 -4.216767E-14 1.022953E-16 14 46.045 -86.478980 9.842937E-05 -1.934716E-06 2.774638E-08 -2.771542E-10 1.681430E-12 -5.587980E-15 7.528435E-18 15 46.045 -86.478980 9.842937E-05 -1.934716E-06 2.774638E-08 -2.771542E-10 1.681430E-12 -5.587980E-15 7.528435E-18

[0060] 7 is a cross-sectional view of a bifocal lens 40 of Example 2. This bifocal lens 40 has a total length, i.e., a lens length, of 55 mm, LL / HI≈5.78, and a bifocal difference of 1.25 times.

[0061] The bifocal lens 40 enlarges and projects an image on a display surface such as the liquid crystal panel 29G at a magnification according to the distance to the screen. The bifocal lens 40 includes, in order from the screen on the enlarged side, a first lens group 41 with negative refractive power, a second lens group 42 with positive refractive power, a third lens group 43 with negative refractive power, a fourth lens group 44 with positive refractive power, and a fifth lens group 45 with positive refractive power. A prism PR is disposed between the fifth lens group 45 and the liquid crystal panel 29G.

[0062] As shown in Fig. 8, when the magnification of the bifocal lens 40 is changed, the first lens group 41 and the fifth lens group 45 are fixed, and the second lens group 42 to the fourth lens group 44 move, and the bifocal lens 40 is approximately telecentric on the reduction side. wide The second lens group 42 to the fourth lens group 44 are disposed on the reduction side closer to the liquid crystal panel 29G. tele The second lens group 42 to the fourth lens group 44 move as a whole toward the enlargement side toward the screen while changing the intervals between adjacent lens groups.

[0063] Returning to FIG. 7, the first lens group 41 is made of a plastic negative aspherical lens, and the second lens group 42 is made of a biconvex lens. The third lens group 43 is made of a cemented lens 43u, which is made by cementing a biconcave lens 43a and a positive meniscus lens 43b, from the enlargement side. The fourth lens group 44 is made of a cemented lens 44u and a biconvex lens 44c, which is made by cementing a biconcave lens 44a and a biconvex lens 44b, from the enlargement side. The fifth lens group 45 is made of a plastic positive aspherical lens. The second lens group 42 to the fourth lens group 44 are made of glass.

[0064] Fig. 9 is a diagram showing the lateral chromatic aberration characteristics of the bifocal lens of Example 2. In Fig. 9, region CR1 shows the lateral chromatic aberration characteristics at the wide-angle end (focal length fw = 16.50 mm), region CR2 shows the lateral chromatic aberration characteristics at the intermediate region (focal length fm = 18.56 mm) which is the intermediate position, and region CR3 shows the lateral chromatic aberration characteristics at the telephoto end (focal length ft = 20.63 mm). Regarding the lateral chromatic aberration characteristics of the bifocal lens of Example 2, the larger of the aberration amounts at the wide-angle end and the telephoto end, that is, the aberration amount at the telephoto end, is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end.

[0065] Fig. 10 is a diagram showing the longitudinal aberration characteristics (i.e., spherical aberration characteristics, astigmatism characteristics, and distortion aberration characteristics) of the bifocal lens of Example 2. In Fig. 10, region DR1 indicates the longitudinal aberration at the wide-angle end (focal length fw = 16.50 mm), region DR2 indicates the longitudinal aberration in the intermediate region (focal length fm = 18.56 mm) which is the intermediate position, and region DR3 indicates the longitudinal aberration at the telephoto end (focal length ft = 20.63 mm). Regarding the spherical aberration characteristics and astigmatism characteristics of the bifocal lens of Example 2, the larger of the aberration amounts at the wide-angle end and the telephoto end is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end.

[0066] Example 3 The lens surface data for Example 3 is shown in Table 7 below. [Table 7] Surface number RD Nd Vd 0 Infinity 1800.00 1* -10.133 2.4887 1.535038 55.7111 2* -22.915 29.3539 3 28.145 2.6148 1.834000 37.1611 4 -92.642 4.2838 5 -46.273 1.2000 1.723420 37.9561 6 18.873 2.0000 1.922860 20.8801 7 37.160 1.0000 8(STO) Infinity 9.6047 9 -29.859 1.2000 1.728250 28.4611 10 16.595 4.6015 1.552001 70.6971 11 -174.231 0.1000 12 38.008 6.6002 1.497000 81.5461 13 -25.039 0.5000 14 -638.475 3.0431 1.772499 49.5981 15 -69.320 0.1000 16* 42.824 5.0000 1.535038 55.7111 17* -129.505 6.0000 18 Infinity 24.7200 1.516331 64.1421 19 Infinity 7.5893 20 Infinity 0.0075

[0067] Table 8 below shows the values ​​of on-axis surface spacing D at variable spacing locations on the lens surfaces at the wide-angle end (wide), the middle position (middle), and the telephoto end (tele) for Example 3. [Table 8] Room number wide middle tele 2 29.354 14.684 8.736 4 4.284 7.610 10.712 7 1.000 1.000 1.000 8 9.605 8.108 1.097 15 0.100 12.941 22.797 19 7.589 7.634 7.517

[0068] Table 9 below lists the aspheric coefficients of the lens surfaces of Example 3. [Table 9] Aspheric coefficients Surface number RK A4 A6 A8 A10 A12 A14 A16 A18 1 -10.133 -3.538418 5.475344E+01 -2.539242E+02 9.168549E+02 -2.453128E+03 4.629721E+03 -5.876214E+03 4.704436E+03 -2.112575E+03 2 -22.915 0.000000 3.504498E+01 -6.635079E+01 4.496130E+01 3.478975E+02 -1.640489E+03 3.678785E+03 -4.723227E+03 3.320749E+03 16 42.824 1.156811 -2.050272E+00 -6.937979E+00 3.044472E+01 -1.017974E+02 1.805938E+02 -1.796240E+02 7.532349E+01 1.619822E+01 17 -129.505 28.206231 -1.619746E+00 -6.456633E+00 2.981016E+01 -9.702201E+01 1.700112E+02 -1.625106E+02 6.355576E+01 1.343087E+01

[0069] 11 is a cross-sectional view of a bifocal lens 40 of Example 3. This bifocal lens 40 has a total length, i.e., a lens length, of 73.7 mm, LL / HI≈7.75, and a bifocal difference of 2.00 times.

[0070] The bifocal lens 40 enlarges and projects an image on a display surface such as the liquid crystal panel 29G at a magnification according to the distance to the screen. The bifocal lens 40 includes, in order from the screen on the enlarged side, a first lens group 41 with negative refractive power, a second lens group 42 with positive refractive power, a third lens group 43 with negative refractive power, a fourth lens group 44 with positive refractive power, and a fifth lens group 45 with positive refractive power. A prism PR is disposed between the fifth lens group 45 and the liquid crystal panel 29G.

[0071] As shown in Fig. 12, when the magnification of the bifocal lens 40 is changed, the first lens group 41 and the fifth lens group 45 are fixed, and the second lens group 42 to the fourth lens group 44 move, and the bifocal lens 40 is approximately telecentric on the reduction side. wide The second lens group 42 to the fourth lens group 44 are disposed on the reduction side closer to the liquid crystal panel 29G. tele The second lens group 42 to the fourth lens group 44 move as a whole toward the enlargement side toward the screen while changing the intervals between adjacent lens groups.

[0072] Returning to FIG. 11, the first lens group 41 is made of a plastic negative aspherical lens, and the second lens group 42 is made of a biconvex lens. The third lens group 43 is made of a cemented lens 43u, which is made by cementing a biconcave lens 43a and a positive meniscus lens 43b, from the enlargement side. The fourth lens group 44 is made of a cemented lens 44u, a biconvex lens 44c, and a positive meniscus lens 44d, which is made by cementing a biconcave lens 44a and a biconvex lens 44b, from the enlargement side. The fifth lens group 45 is made of a plastic positive aspherical lens. The second lens group 42 to the fourth lens group 44 are made of glass.

[0073] Fig. 13 is a diagram showing the lateral chromatic aberration characteristics of the bifocal lens of Example 3. In Fig. 13, region ER1 shows the lateral chromatic aberration characteristics at the wide-angle end (focal length fw = 16.51 mm), region ER2 shows the lateral chromatic aberration characteristics at the intermediate region (focal length fm = 24.70 mm) which is the intermediate position, and region ER3 shows the lateral chromatic aberration characteristics at the telephoto end (focal length ft = 32.80 mm). Regarding the lateral chromatic aberration characteristics of the bifocal lens of Example 3, the larger of the aberration amounts at the wide-angle end and the telephoto end, that is, the aberration amount at the wide-angle end, is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end.

[0074] Fig. 14 is a diagram showing the longitudinal aberration characteristics (i.e., spherical aberration characteristics, astigmatism characteristics, and distortion aberration characteristics) of the bifocal lens of Example 3. In Fig. 14, region FR1 shows the longitudinal aberration at the wide-angle end (focal length fw = 16.51 mm), region FR2 shows the longitudinal aberration in the intermediate region (focal length fm = 24.70 mm) which is the intermediate position, and region FR3 shows the longitudinal aberration at the telephoto end (focal length ft = 32.80 mm). Regarding the spherical aberration characteristics of the bifocal lens of Example 3, the larger of the aberration amount at the wide-angle end and the aberration amount at the telephoto end, that is, the aberration amount at the telephoto end, is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end. Regarding the astigmatism characteristics of the bifocal lens of Example 3, the larger of the aberration amounts at the wide-angle end and the telephoto end, that is, the aberration amount at the telephoto end, is smaller than the aberration amount in the intermediate region between the wide-angle end and the telephoto end.

[0075] For reference, the following Table 10 summarizes the values ​​of Examples 1 to 3 corresponding to each of the conditional expressions (1) to (4). [Table 10] TIFF2025070042000003.tif28167

[0076] Second Embodiment A bifocal lens according to a second embodiment of the present invention and an imaging device incorporating the same will be described below.

[0077] As shown in FIG. 15, an imaging device 202 incorporating a bifocal lens 240 according to the second embodiment includes an optical system portion 250 that captures an image of a target, and a circuit device 90 that controls the operation of the optical system portion 250.

[0078] The optical system part 250 includes a bifocal lens 240 and an image sensor 229. Here, the bifocal lens 240 is the same as the bifocal lens 40 according to the first embodiment shown in FIG. 2. The image sensor 229 is, for example, a CMOS type image sensor, and has a photoelectric conversion unit 229a, around which a signal processing circuit (not shown) is formed. In the photoelectric conversion unit 229a, pixels, that is, photoelectric conversion elements, are arranged two-dimensionally. Note that the image sensor 229 is not limited to the above-mentioned CMOS type image sensor, and may incorporate other image sensors such as CCD. The image sensor 229 or the photoelectric conversion unit 229a is arranged on the reduction side conjugate plane RC of the bifocal lens 240.

[0079] The circuit device 90 includes an element driver 91, a lens driver 93, an input unit 95, a storage unit 96, a display unit 97, and a main controller 98. The element driver 91 operates the image sensor 229 by outputting a control signal to a circuit associated with the image sensor 229. The lens driver 93 operates under the control of the main controller 98, and can change the state of the bifocal lens 240 between the wide-angle end and the telephoto end by appropriately moving some optical elements constituting the bifocal lens 240 along the optical axis OA via an actuator AC. The input unit 95 is a unit that accepts user operations, the storage unit 96 is a unit that stores information necessary for the operation of the image sensor 202, image data acquired by the optical system unit 250, and the like, and the display unit 97 is a unit that displays information to be presented to the user, captured images, and the like. The main control unit 98 comprehensively controls the operation of the element driving unit 91, lens driving unit 93, input unit 95, memory unit 96, display unit 97, etc., and can perform various image processing on image data obtained by the optical system part 250.

[0080] [Other matters] The above-described structure is merely an example, and various modifications can be made within the scope of achieving the same function.

[0081] For example, in each embodiment, one or more lenses having substantially no power can be added before or after the lenses constituting each lens group.

[0082] Furthermore, the subject of enlarged projection by the bifocal lens 40 is not limited to images formed by a liquid crystal panel; images formed by a light modulation element such as a digital micromirror device can also be enlarged and projected.

[0083] Summary of the Disclosure The following is a summary of this disclosure.

[0084] (Appendix 1) A bifocal lens is composed of a plurality of lens groups, and the focal position changes by changing the position of the lens groups, and in terms of the lateral chromatic aberration characteristics of the bifocal lens, the larger of the aberration amounts at the wide-angle end and the telephoto end is smaller than the aberration amount in an intermediate region between the wide-angle end and the telephoto end. In an optical system that realizes such lateral chromatic aberration characteristics, the lens power of each lens group can be increased, so the amount of movement of the lens group when realizing multiple focal points can be reduced. As a result, the performance can be maintained while suppressing the increase in the total length of the bifocal lens relative to the image height, i.e., the lens length, and the bifocal lens can be made more compact.

[0085] (Appendix 2) A bifocal lens as described in Appendix 1, which comprises, in order from the enlargement side to the reduction side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, a fourth lens group having positive refractive power, and a fifth lens group having positive refractive power, and the lens group on the reduction side from the fifth lens group is telecentric. In the above compound focal length lenses, the first lens group has negative refractive power, and the second and subsequent lens groups have positive refractive power overall, so that it is possible to realize a wide angle and a long back focus while avoiding an increase in the diameter of the first lens group. Also, the second lens group corrects the lateral chromatic aberration caused by the first lens group, the negative power of the third lens group corrects the positive lateral chromatic aberration caused by the fourth and fifth lens groups, and the fourth and fifth lens groups ensure that the reduction side beyond the fifth lens group is telecentric, thereby realizing good aberration characteristics.

[0086] (Appendix 3) The bifocal lens according to claim 2, wherein, during magnification change, the first lens group and the fifth lens group are fixed, and the second lens group, the third lens group and the fourth lens group move from the reduction side to the enlargement side independently of each other. During magnification change, the first and fifth lens groups remain fixed, and only the second to fourth lens groups move independently of one another, so the overall length of the bifocal lens does not change, and the structure of the lens barrel that holds the bifocal lens can be simplified.

[0087] (Appendix 4) A bifocal lens described in any one of Appendices 1 to 3, wherein, regarding the spherical aberration characteristics of the bifocal lens, the larger of the amount of aberration at the wide-angle end and the amount of aberration at the telephoto end is smaller than the amount of aberration in an intermediate region between the wide-angle end and the telephoto end. In an optical system that realizes such spherical aberration characteristics, the power of the lens group can be increased, so that the bifocal lens can be made more compact. In particular, better aberration characteristics can be obtained at the wide-angle and telephoto ends.

[0088] (Appendix 5) 5. The bifocal lens according to claim 1, wherein the ratio of the focal length of the entire system at the wide-angle end to the focal length of the entire system at the telephoto end is 1.20 or greater. Such a bifocal lens is a compact optical system in which the overall length of the bifocal lens is short relative to the image height, yet has a large focal difference between the wide-angle end and the telephoto end.

[0089] (Appendix 6) A bifocal lens according to any one of Appendices 2 to 5, which satisfies the following conditional formula: 1.0≦|fG1 / fG2| … (1) Where: fG1: focal length of the first lens group fG2: focal length of the second lens group Like the bifocal lens described above, making the power of the second lens group equal to or stronger than that of the first lens group, in other words, making the bifocal difference (magnification difference) larger, contributes to shortening the overall length.

[0090] (Appendix 7) A bifocal lens according to any one of claims 2 to 6, which satisfies the following conditional formula: 0.10≦M4 / LL≦0.35 … (2) Where: M4: Amount of movement of the 4th lens group from the wide-angle end to the telephoto end LL: Lens length As in the above bifocal lens, by relatively increasing the amount of movement of the fourth lens group, it is possible to increase the bifocal difference (magnification difference) while contributing to shortening the overall length. By setting the value M4 / LL of the above conditional expression to the lower limit or higher, it becomes easy to obtain a bifocal difference (magnification difference). By setting the value M4 / LL of the above conditional expression to the upper limit or lower, it is possible to avoid the problem of the overall length becoming large and various aberrations becoming worse. Note that an aperture is usually disposed between the third lens group and the fourth lens group, and a large amount of movement of the fourth lens group can be considered to mean a large amount of movement of the part behind the aperture, i.e., on the reduction side.

[0091] (Appendix 8) A bifocal lens according to any one of Appendices 2 to 7, which satisfies the following conditional formula: AVνd1 / AVνd2≦0.80 … (3) Where: AVνd1: average Abbe number for the d line of the first lens group AVνd2: Average Abbe number for the d line of the second lens group In the bifocal lens described above, it is possible to effectively correct chromatic aberration while achieving compactness. Furthermore, if the second group is a single lens, compactness can be achieved more easily.

[0092] (Appendix 9) A bifocal lens according to any one of claims 1 to 8, which satisfies the following conditional formula: LL / HI≦8.0 … (4) Where: LL: Lens length HI: Image height Satisfying the above conditions can contribute to miniaturization of the bifocal lens.

[0093] (Appendix 10) A bifocal lens according to any one of claims 1 to 9; an image forming unit that forms a projection image on a reduction-side conjugate plane of the bifocal lens; The image forming section is a projector having a light source device and a light modulation element that modulates light from the light source device. This makes it possible to realize a compact projector equipped with a bifocal lens.

[0094] (Appendix 11) A bifocal lens according to any one of claims 1 to 9; and an image sensor disposed on a reduction-side conjugate plane of the bifocal lens. This makes it possible to realize a compact imaging device equipped with a bifocal lens. [Explanation of symbols]

[0095] 2...projector, 10...light source device, 20a...image forming section, 23, 24...relay lens, 25, 26, 27...reflection mirror, 28B, 28G, 28R...field lens, 29B, 29G, 29R...liquid crystal panel, 31...cross dichroic prism, 40...bifocal lens, 41, 42, 43, 44, 45...lens group, 43a...biconcave lens, 43b...meniscus lens, 43u...cemented lens, 44a...biconcave lens, 44b...biconvex lens, 44c...biconvex lens, 44d...meniscus Lens, 44u... cemented lens, 50... optical system portion, 80... circuit device, 81... image processing portion, 82... display drive portion, 83... lens drive portion, 88... main control portion, 90... circuit device, 91... element drive portion, 93... lens drive portion, 95... input portion, 96... memory portion, 97... display portion, 98... main control portion, 202... imaging device, 229... imaging element, 229a... photoelectric conversion portion, 240... bifocal lens, 250... optical system portion, AC... actuator, OA... optical axis, PR... prism, RC... reduction side conjugate surface, ST... aperture stop

Claims

1. A bifocal lens is composed of a plurality of lens groups, and the focal position changes by changing the position of the lens groups, Regarding the lateral chromatic aberration characteristic of the bifocal lens, the larger of the aberration amount at the wide-angle end and the aberration amount at the telephoto end is smaller than the aberration amount in an intermediate region between the wide-angle end and the telephoto end. Bifocal lens.

2. The optical system comprises, in order from the magnification side to the reduction side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, a fourth lens group having positive refractive power, and a fifth lens group having positive refractive power. the reduction side of the fifth lens group is telecentric; 2. The bifocal lens according to claim 1.

3. During magnification change, the first lens group and the fifth lens group are fixed, and the second lens group, the third lens group and the fourth lens group move from the reduction side toward the enlargement side independently of one another.

3. The bifocal lens according to claim 2.

4. Regarding the spherical aberration characteristic of the bifocal lens, the larger of the aberration amount at the wide-angle end and the aberration amount at the telephoto end is smaller than the aberration amount in an intermediate region between the wide-angle end and the telephoto end.

2. The bifocal lens according to claim 1.

5. a ratio of a focal length of the entire system at the wide-angle end to a focal length of the entire system at the telephoto end is 1.20 or more; 2. The bifocal lens according to claim 1.

6. 3. The bifocal lens according to claim 2, which satisfies the following conditional expression: 1.0≦|fG1 / fG2|… (1) Where: fG1: focal length of the first lens group fG2: the focal length of the second lens group

7. 3. The bifocal lens according to claim 2, which satisfies the following conditional expression: 0.10≦M4 / LL≦0.35 … (2) Where: M4: the movement amount of the fourth lens group from the wide-angle end to the telephoto end LL: Lens length

8. 3. The bifocal lens according to claim 2, which satisfies the following conditional expression: AVνd1 / AVνd2≦0.80… (3) Where: AVνd1: average Abbe number for the d line of the first lens group AVνd2: average Abbe number for the d line of the second lens group

9. 2. The bifocal lens according to claim 1, which satisfies the following conditional expression: LL / HI≦8.0… (4) Where: LL: Lens length HI: Image height

10. A bifocal lens according to claim 1; an image forming unit that forms a projection image on a reduction-side conjugate surface of the bifocal lens; The image forming unit includes a light source device and a light modulation element that modulates light from the light source device. projector.

11. A bifocal lens according to claim 1; and an image sensor disposed on a reduction-side conjugate surface of the bifocal lens. Imaging device.

Images