JP2010249946A - Lens system and optical equipment equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens system where aberrations are satisfactorily corrected though an optical system is compact. <P>SOLUTION: In constitution having five lenses being first to fifth lenses L1 to L5 arranged in order from a projection side along an optical axis, the third lens L3 and the fourth lens L4 are stuck to form a cemented lens L34, and the first lens L1 is a biconvex lens. When a focal length of the first lens L1 is defined as f1, and a focal length of the entire lens system is defined as f, the lens system satisfies a condition shown by a following expression: 1.65<f1/f<2.40. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention particularly relates to a lens system suitable for a projector for projecting an image displayed on an image display element or the like onto a screen, and an optical apparatus equipped with the lens system.

  Conventionally, projector apparatuses that use an image display element such as a liquid crystal element and project an image based on the display element on a screen are often used, and there are various projector lenses that can display a high-definition image. It has been proposed (see, for example, Patent Document 1).

JP 2005-31015 A

  In recent years, there has been a demand for miniaturization and miniaturization of projector apparatuses. To that end, a lens system (projection lens) used in the projector apparatus needs to be miniaturized. In order to realize such a compact projector, there is a demand for a lens system configured with a small number of components while correcting various aberrations and maintaining performance.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a lens system in which various aberrations are favorably corrected while the optical system is small, and an optical apparatus on which the lens system is mounted. .

  In order to achieve such an object, the lens system of the first aspect of the present invention has a configuration in which the third lens system includes five lenses of first to fifth lenses arranged in order from the projection side along the optical axis. When the lens and the fourth lens are bonded to form a cemented lens, the first lens is a biconvex lens, the focal length of the first lens is f1, and the focal length of the entire lens system is f. The condition of Expression 1.65 <f1 / f <2.40 is satisfied.

  A lens system according to a second aspect of the present invention has a configuration including five lenses of first to fifth lenses arranged in order from the projection side along the optical axis, and the third lens and the fourth lens, Are combined to form a cemented lens, the focal length of the first lens is f1, and the focal length of the entire lens system is f. The condition of the following formula 1.65 <| f1 / f | <2.05 is satisfied. Satisfied.

  When the radius of curvature of the lens surface on the projection side of the third lens is R3, it is preferable that the condition of the following expression -2.45 <R3 / f <-1.60 is satisfied.

  The distance on the optical axis from the lens surface on the projection side of the third lens to the lens surface on the object side of the fourth lens is T34, and the lens on the most object side from the lens surface on the most projection side in the entire lens system. When the distance on the optical axis to the surface is T, it is preferable to satisfy the following condition: 0.30 <T34 / T <0.52.

  Further, when the refractive index of the second lens with respect to the d-line is nd2, it is preferable that the condition of the following formula 1.56 <nd2 <1.62 is satisfied.

  Further, when the Abbe number of the second lens with respect to the d-line is νd2, it is preferable that the condition of the following expression 25.0 <νd2 <35.0 is satisfied.

  Further, when the refractive index of the fifth lens with respect to the d-line is nd5, it is preferable that the condition of the following formula 1.52 <nd5 <1.55 is satisfied.

  Further, when the Abbe number of the fifth lens with respect to the d-line is νd5, it is preferable that the condition of the following expression 54.0 <νd5 <58.0 is satisfied.

  Moreover, it is preferable that at least one of the second lens and the fifth lens is a plastic lens.

  In addition, it is preferable that at least one of the second lens and the fifth lens is an aspheric lens.

  Moreover, it is preferable that an aperture stop is provided between the second lens and the third lens.

  In the second aspect of the present invention, it is preferable that the first lens has a positive refractive power.

  An optical apparatus according to the present invention includes the lens system having the above-described configuration.

  According to the present invention, it is possible to provide a lens system in which various aberrations are satisfactorily corrected while the number of optical systems is small, and high optical performance is obtained over the entire projection surface, and an optical apparatus including the lens system.

It is a block diagram of the lens system which concerns on 1st Example. FIG. 6 is a diagram illustrating all aberrations of the lens system according to Example 1; It is a block diagram of the lens system which concerns on 2nd Example. FIG. 7 is a diagram illustrating all aberrations of the lens system according to Example 2. It is a block diagram of the lens system which concerns on 3rd Example. FIG. 10 is a diagram illustrating all aberrations of the lens system according to Example 3. It is a block diagram of the lens system which concerns on 4th Example. FIG. 12 is a diagram illustrating all aberrations of the lens system according to Example 4; 1 is a configuration diagram of a projector having a lens system according to the present embodiment.

  Hereinafter, preferred embodiments will be described with reference to the drawings. As shown in FIG. 1, the lens system PL according to the present embodiment is a projection lens, and includes five lenses of first to fifth lenses L1 to L5 arranged in order from the projection side along the optical axis. In the configuration, the third lens L3 and the fourth lens L4 are bonded to form a cemented lens L34.

  As described above, the lens system PL according to the present embodiment includes five lenses as a basic configuration, and has a small and compact configuration with a short overall length of the optical system. It is the structure which can correct | amend to.

  In the present embodiment, when the first lens L1 is a biconvex lens based on the above configuration, the focal length of the first lens L1 is f1, and the focal length of the entire lens system is f, the following formula ( Satisfy the condition of 1).

  1.65 <f1 / f <2.40 (1)

  The conditional expression (1) is a conditional expression for defining the focal length of the first lens L1 with respect to the focal length of the entire lens system. By satisfying this conditional expression (1), the Petzval sum can be adjusted appropriately, and spherical aberration and curvature of field can be corrected well. However, if the upper limit value of the conditional expression (1) is exceeded, the positive power of the first lens L1 becomes too small, and the power must be reduced with a negative lens to correct this refractive power balance. As a result, the Petzval sum increases positively, and the curvature of field cannot be completely corrected, so that the imaging performance is deteriorated. On the other hand, if the lower limit value of the conditional expression (1) is not reached, the positive power of the first lens L1 becomes too large, and the power must be increased with a negative lens in order to correct this refractive power balance. As a result, the Petzval sum increases negatively, and spherical aberration, coma aberration, etc. remain due to overcorrection, and the imaging performance is deteriorated.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 2.39. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 1.70.

  Further, in the present embodiment, based on the above configuration, when the focal length of the first lens L1 is f1 and the focal length of the entire lens system is f, the configuration satisfying the condition of the following expression (2) may be used. Good.

  1.65 <| f1 / f | <2.05 (2)

  The conditional expression (2) is a conditional expression for defining the focal length of the first lens L1 with respect to the focal length of the entire lens system. By satisfying this conditional expression (2), the Petzval sum can be adjusted appropriately and spherical aberration and field curvature can be corrected well. However, if the upper limit value of conditional expression (2) is exceeded, the positive power of the first lens L1 becomes too small, and the power must be reduced with a negative lens in order to correct this refractive power balance. As a result, the Petzval sum increases positively, and the curvature of field cannot be completely corrected, so that the imaging performance is deteriorated. On the other hand, if the lower limit value of the conditional expression (2) is not reached, the positive power of the first lens L1 becomes too large, and the power must be increased by a negative lens in order to correct this refractive power balance. As a result, the Petzval sum increases negatively, and spherical aberration, coma aberration, etc. remain due to overcorrection, and the imaging performance is deteriorated.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 2.04. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 1.68.

  In the present embodiment, it is preferable that the condition of the following expression (3) is satisfied when the curvature radius of the lens surface on the projection side of the third lens L3 is R3.

  -2.45 <R3 / f <-1.60 (3)

  The conditional expression (3) is a conditional expression for defining the radius of curvature of the third lens L3 with respect to the focal length of the entire lens system. By satisfying the conditional expression (3), it is possible to improve the light flux balance between the on-axis and off-axis, and to correct the coma aberration and the field curvature well. Exceeding the upper limit of conditional expression (3) is not preferable because the astigmatic difference increases and it becomes difficult to achieve high optical performance. On the other hand, if the lower limit value of conditional expression (3) is not reached, the balance between the on-axis and off-axis light beams is lost, and it is difficult to correct coma and field curvature, which is not preferable.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to −1.65. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to −2.15.

  In the present embodiment, the distance on the optical axis from the lens surface on the projection side of the third lens L3 to the lens surface on the object side of the fourth lens L4 is T34, and the lens surface on the most projection side in the entire lens system. When the distance on the optical axis from the lens surface closest to the object side is T, it is preferable to satisfy the condition of the following expression (4).

  0.30 <T34 / T <0.52 (4)

  The conditional expression (4) is a conditional expression for defining the distance T34 on the optical axis of the cemented lens including the third and fourth lenses L3 and L4 with respect to the distance T on the optical axis of the entire lens system. By satisfying the conditional expression (4), a substantially telecentric optical system can be realized, and the peripheral light amount, coma aberration, and field curvature can be favorably corrected. On the other hand, if the conditional expression (4) cannot be satisfied, the relationship of the substantially telecentric optical system is broken, and it becomes difficult to correct the peripheral light amount, coma aberration, and field curvature, and it is difficult to realize high optical performance. It is not preferable.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (4) to 0.50. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.45.

  In the present embodiment, it is preferable that the condition of the following expression (5) is satisfied when the refractive index of the second lens L2 with respect to the d-line is nd2.

  1.56 <nd2 <1.62 (5)

  Conditional expression (5) defines an appropriate range of the refractive index nd2 of the second lens L2. By satisfying conditional expression (5), it is possible to secure a sufficient enlargement ratio and angle of view, and to correct field curvature well. Exceeding the upper limit value of conditional expression (5) is not preferable because it is difficult to correct curvature of field and to achieve high optical performance. On the other hand, if the lower limit of conditional expression (5) is not reached, it is difficult to ensure a sufficient enlargement ratio and angle of view, and in this case too, it is difficult to achieve high optical performance, which is not preferable.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (5) to 1.61. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (5) to 1.58.

  In the present embodiment, it is preferable that the condition of the following expression (6) is satisfied when the Abbe number of the second lens L2 with respect to the d-line is νd2.

  25.0 <νd2 <35.0 (6)

  The conditional expression (6) defines an appropriate range of the Abbe number νd2 of the second lens L2. By satisfying this conditional expression (6), it is possible to satisfactorily correct chromatic aberration (axial chromatic aberration and lateral chromatic aberration). On the other hand, when the conditional expression (6) cannot be satisfied, it is not preferable because sufficient chromatic aberration correction cannot be performed and it becomes difficult to realize high optical performance.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (6) to 30.5. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (6) to 26.5.

  In the present embodiment, it is preferable that the condition of the following formula (7) is satisfied when the refractive index of the fifth lens L5 with respect to the d-line is nd5.

  1.52 <nd5 <1.55 (7)

  Conditional expression (7) defines an appropriate range of the refractive index nd5 of the fifth lens L5. By satisfying conditional expression (7), it is possible to secure a sufficient enlargement ratio and angle of view, and to correct field curvature well. Exceeding the upper limit value of conditional expression (7) is not preferable because it is difficult to correct curvature of field and to achieve high optical performance. On the other hand, if the lower limit value of conditional expression (7) is not reached, it becomes difficult to correct curvature of field, and a sufficient enlargement ratio and angle of view cannot be ensured. In this case as well, high optical performance can be realized. Since it becomes difficult, it is not preferable.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (7) to 1.54. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (7) to 1.53.

  In the present embodiment, it is preferable that the condition of the following formula (8) is satisfied when the Abbe number of the fifth lens L5 with respect to the d-line is νd5.

  54.0 <νd5 <58.0 (8)

  The conditional expression (8) defines an appropriate range of the Abbe number νd5 of the fifth lens L5. By satisfying this conditional expression (8), it is possible to satisfactorily correct chromatic aberration (axial chromatic aberration and lateral chromatic aberration). On the other hand, when the conditional expression (8) cannot be satisfied, it is not preferable because sufficient chromatic aberration correction cannot be performed and it is difficult to realize high optical performance.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (8) to 56.5. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (8) to 55.5.

  In the present embodiment, it is preferable that at least one of the second lens L2 and the fifth lens L5 is a plastic lens. Here, since the plastic lens is manufactured by molding such as injection molding, even if the surface shape is an aspherical surface, it is not difficult to manufacture compared to a spherical surface, and the cost is hardly increased. Therefore, for example, by making the second lens L2 and the fifth lens L5 having aspheric surfaces plastic, it is possible to reduce the manufacturing cost and reduce the weight of the entire lens system compared to the case of using a glass mold aspheric lens. Can be achieved.

  In the present embodiment, it is preferable that at least one of the second lens L2 and the fifth lens L5 is an aspheric lens. This configuration is preferable because at least one of spherical aberration and distortion can be corrected satisfactorily.

  In the present embodiment, it is preferable that an aperture stop S is provided between the second lens L2 and the third lens L3. This configuration is preferable because extra light can be limited and coma can be reduced.

  In the present embodiment, it is preferable that the first lens L1 has a positive refractive power. This configuration is preferable because distortion can be corrected satisfactorily.

  FIG. 9 shows a configuration of a single-plate liquid crystal projector as an optical apparatus including the lens system PL having the above configuration. The projector 1 includes an illumination optical system 10, a polarization beam splitter PBS, an image display element (reflection type liquid crystal display element) LCD, and the lens system PL. The illumination optical system 10 includes light sources 11R, 11G, and 11B, a plurality of condenser lenses CL1, CL1,..., A dichroic mirror 12, 13, a quarter wavelength plate 14, and a condenser lens CL2.

  In the illumination optical system 10, the light beams (red light, green light, and blue light) emitted from the light sources 11R, 11G, and 11B are collected by the condenser lenses CL1 and arranged on the optical path. , 13 is transmitted or reflected and enters the quarter-wave plate 14. The light beam that has passed through the quarter-wave plate 14 is converted into a parallel light beam by the condenser lens CL2, and is reflected by changing the direction by approximately 90 ° by the polarization beam splitter PBS to illuminate the image display element LCD.

  Then, the light beam (video light) spatially modulated and reflected by the image display element LCD according to the input image information is transmitted through the polarization beam splitter PBS, enlarged and projected on a screen (not shown) by the lens system PL. An image is displayed.

  In the present embodiment, the projector 1 using the reflective liquid crystal display element as the image display element LCD has been described as an example. However, a transmissive liquid crystal display element or a digital micromirror device (DMD) is used as the image display element. May be configured.

  Hereinafter, each example according to the present embodiment will be described with reference to the drawings. 1, 3, 5, and 7 are cross-sectional views illustrating the configuration of the lens system PL according to each embodiment. As described above, each of the lens systems PL according to each embodiment includes a first lens L1 having a biconvex shape and a positive refractive power, arranged in order from the projection side along the optical axis, and a negative meniscus shape. Joint having positive refractive power obtained by joining the second lens L2 having refractive power, the third lens L3 having negative refractive power with a biconcave shape, and the fourth lens L4 having positive refractive power with biconvex shape. It has a lens L34 and a fifth lens L5 that is biconvex and has positive refractive power.

  Tables 1 to 4 are shown below, but these are tables of specifications in the first to fourth examples. In [Lens Data], the surface number is the order of the lens surfaces from the projection side, r is the radius of curvature of each lens surface, and d is the surface on the optical axis from each optical surface to the next optical surface. Nd represents the refractive index with respect to the d-line (wavelength 587.6 nm), and νd represents the Abbe number with respect to the d-line. When the lens surface is aspherical, an asterisk is attached to the surface number, and the paraxial radius of curvature is indicated in the column of the radius of curvature r. The radius of curvature “0.0000” indicates a plane or an opening. Further, the description of the refractive index “1.00000” of air is omitted.

In [Aspherical Data], the shape of the aspherical surface shown in [Lens Data] is shown by the following equation (a). That is, y is the height in the direction perpendicular to the optical axis, and S (y) is the distance (sag amount) along the optical axis from the tangent plane at the apex of the aspheric surface to the position on the aspheric surface at height y. When the radius of curvature (paraxial radius of curvature) of the reference spherical surface is r, the conic coefficient is K, and the n-th aspherical coefficient is An, the following equation (a) is given. In each embodiment, the secondary aspheric coefficient A2 is 0, and the description thereof is omitted. Further, En represents × 10 ^n. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ .

S (y) = (y ² / r) / {1+ (1−K · y ² / r ² ) ^1/2 }
+ A4 × y ⁴ + A6 × y ⁶ (a)

  In [various data], f is the focal length of the entire lens system, NA is the numerical aperture on the object side, ω is the half angle of view on the projection side, β is the projection magnification of the entire lens system, and f1 is the first lens. The focal length of L1 is shown. In [Conditional Expression], the conditional expressions (1) to (8) and values corresponding thereto are shown.

  In the table, “mm” is generally used as the unit of focal length f, radius of curvature r, surface interval d, and other lengths. However, since the optical system can obtain the same optical performance even when proportionally enlarged or proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used.

  The description of the above table is the same in other examples, and the description thereof is omitted.

(First embodiment)
The lens system according to the first example will be described with reference to FIGS. 1 and 2 and Table 1. FIG. As shown in FIG. 1, the lens system PL1 according to the first example includes a first lens L1 having a positive refractive power and a second lens having a negative refractive power arranged in order from the projection side along the optical axis. It has a lens L2, a third lens L3 having a negative refractive power, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a positive refractive power.

  The first lens L1 is a biconvex positive lens whose projection side has a stronger refractive index than the object side. The second lens L2 is a negative meniscus lens in which an aspherical surface is formed on the lens surface on the projection side, and the projection surface has a convex surface facing the projection side having a weak refractive index compared to the object side. The third lens L3 is a biconcave negative lens whose projection side has a lower refractive index than the object side. The fourth lens L4 is a biconvex positive lens having a lower refractive index on the projection side than on the object side. The fifth lens L5 is a biconvex positive lens in which an aspherical surface is formed on the lens surface on the projection side. The third lens L3 and the fourth lens L4 are bonded to form a cemented lens L34 having a positive refractive power as a whole. An aperture stop S is disposed between the second lens L2 and the third lens L3.

  In addition, on the object side of the fifth lens L5, a parallel flat glass GB corresponding to a color synthesis prism and an image display element LCD such as a liquid crystal panel are arranged.

  Table 1 shows a table of specifications in the first embodiment. The surface numbers 1 to 12 in Table 1 correspond to the surfaces 1 to 12 shown in FIG. In the first embodiment, each of the third and ninth lens surfaces is formed in an aspherical shape.

(Table 1)
[Lens data]
Surface number r d nd νd
1 14.8000 2.7500 1.728250 28.46
2 -136.2000 1.2500
* 3 19.9530 1.9500 1.582760 30.34
4 3.9310 1.6000
5 0.0000 0.5000 (Aperture stop S)
6 -22.6070 5.2000 1.728250 28.46
7 13.5397 6.5000 1.618000 63.37
8 -7.5600 0.7000
* 9 15.7960 5.5000 1.531130 55.73
10 -34.9160 2.0000
11 0.0000 11.0000 1.516800 64.11
12 0.0000 1.0000
[Aspherical data]
3rd surface κ = -5.07580, A4 = -1.20140E-04, A6 = -1.48220E-05
9th surface κ = 0.99161, A4 = -1.13120E-04, A6 = -4.50900E-07
[Various data]
f = 10.695
NA = 0.20
ω = 25.87 °
β = 0.0192
f1 = 18.473
[Conditional expression]
T34 = 11.70
T = 25.95
Conditional expression (1) f1 / f = 1.73
Conditional expression (2) | f1 / f | = 1.73
Conditional expression (3) R3 / f = -2.11
Conditional expression (4) T34 / T = 0.45
Conditional expression (5) nd2 = 1.58
Conditional expression (6) νd2 = 30.3
Conditional expression (7) nd5 = 1.53
Conditional expression (8) νd5 = 55.7

  From the table of specifications shown in Table 1, it can be seen that the lens system PL1 according to the first example satisfies all the conditional expressions (1) to (8).

  FIG. 2 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion aberration diagram, chromatic aberration diagram of magnification, and coma aberration diagram) of the first example. In each aberration diagram, NA represents the numerical aperture on the object side, and H0 represents the object height. D is the d-line (wavelength 587.6 nm), g is the g-line (wavelength 435.8 nm), C is the C-line (wavelength 656.3 nm), and F is the aberrations for the F-line (wavelength 486.1 nm). Indicates various aberrations with respect to the d-line. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the coma aberration diagram, in each incident light, a solid line represents meridional coma aberration with respect to d-line, C-line, g-line, and F-line. The explanation of the above aberration diagrams is the same in the other examples, and the explanation is omitted.

  As is apparent from the respective aberration diagrams, the lens system PL1 according to the first example has a good correction of various aberrations despite the fact that the total length of the optical system is short and the number of lenses is small. It is clear that it has performance.

(Second embodiment)
The lens system according to the second example will be described with reference to FIGS. 3 and 4 and Table 2. FIG. As shown in FIG. 3, the lens system PL2 according to the second example includes a first lens L1 having a positive refractive power and a second lens having a negative refractive power arranged in order from the projection side along the optical axis. It has a lens L2, a third lens L3 having a negative refractive power, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a positive refractive power.

  The first lens L1 is a biconvex positive lens whose projection side has a stronger refractive index than the object side. The second lens L2 is a negative meniscus lens in which an aspherical surface is formed on the lens surface on the projection side, and the projection surface has a convex surface facing the projection side having a weak refractive index compared to the object side. The third lens L3 is a biconcave negative lens whose projection side has a lower refractive index than the object side. The fourth lens L4 is a biconvex positive lens having a lower refractive index on the projection side than on the object side. The fifth lens L5 is a biconvex positive lens in which an aspherical surface is formed on the lens surface on the projection side. The third lens L3 and the fourth lens L4 are bonded to form a cemented lens L34 having a positive refractive power as a whole. An aperture stop S is disposed between the second lens L2 and the third lens L3.

  In addition, on the object side of the fifth lens L5, a parallel flat glass GB corresponding to a color synthesis prism and an image display element LCD such as a liquid crystal panel are arranged.

  Table 2 shows a table of specifications in the second embodiment. The surface numbers 1 to 12 in Table 2 correspond to the surfaces 1 to 12 shown in FIG. In the second embodiment, each of the third and ninth lens surfaces is aspherical.

(Table 2)
[Lens data]
Surface number r d nd νd
1 22.0000 2.2000 1.755199 27.51
2 -65.4700 0.2500
* 3 11.8550 3.9500 1.607100 26.63
4 3.8000 1.2000
5 0.0000 0.2000 (Aperture stop S)
6 -18.0660 5.0000 1.728250 28.46
7 12.2490 6.2500 1.618000 63.37
8 -7.4960 0.2000
* 9 21.1320 4.1000 1.531130 55.73
10 -16.2670 2.5000
11 0.0000 11.0000 1.516800 64.11
12 0.0000 0.7000
[Aspherical data]
3rd surface κ = 1.06821, A4 = -3.01492E-04, A6 = -4.57926E-06
9th surface κ = 2.11701, A4 = -1.05699E-04, A6 = -5.64441E-08
[Various data]
f = 10.844
NA = 0.20
ω = 25.79 °
β = 0.0195
f1 = 22.043
[Conditional expression]
T34 = 11.25
T = 23.35
Conditional expression (1) f1 / f = 2.03
Conditional expression (2) | f1 / f | = 2.03
Conditional expression (3) R3 / f = -1.67
Conditional expression (4) T34 / T = 0.48
Conditional expression (5) nd2 = 1.61
Conditional expression (6) νd2 = 26.6
Conditional expression (7) nd5 = 1.53
Conditional expression (8) νd5 = 55.7

  From the table of specifications shown in Table 2, it can be seen that the lens system PL2 according to the second example satisfies all the conditional expressions (1) to (8).

  FIG. 4 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion aberration diagram, chromatic aberration diagram of magnification, and coma aberration diagram) of the second example. As is apparent from the respective aberration diagrams, the lens system PL2 according to the second example has various aberrations corrected satisfactorily despite the fact that the total length of the optical system is short and the number of lenses is small. It is clear that it has performance.

(Third embodiment)
The lens system according to the third example will be described with reference to FIGS. 5 and 6 and Table 3. FIG. As shown in FIG. 5, the lens system PL3 according to the third example includes a first lens L1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the projection side along the optical axis. It has a lens L2, a third lens L3 having a negative refractive power, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a positive refractive power.

  The first lens L1 is a biconvex positive lens whose projection side has a stronger refractive index than the object side. The second lens L2 is a negative meniscus lens in which an aspherical surface is formed on the lens surface on the projection side, and the projection surface has a convex surface facing the projection side having a weak refractive index compared to the object side. The third lens L3 is a biconcave negative lens whose projection side has a lower refractive index than the object side. The fourth lens L4 is a biconvex positive lens having a lower refractive index on the projection side than on the object side. The fifth lens L5 is a biconvex positive lens in which an aspherical surface is formed on the lens surface on the projection side. The third lens L3 and the fourth lens L4 are bonded to form a cemented lens L34 having a positive refractive power as a whole. An aperture stop S is disposed between the second lens L2 and the third lens L3.

  In addition, on the object side of the fifth lens L5, a parallel flat glass GB corresponding to a color synthesis prism and an image display element LCD such as a liquid crystal panel are arranged.

  Table 3 shows a table of specifications in the third embodiment. In addition, the surface numbers 1-12 in Table 3 respond | correspond to the surfaces 1-12 shown in FIG. In the second embodiment, each of the third and ninth lens surfaces is aspherical.

(Table 3)
[Lens data]
Surface number r d nd νd
1 14.6000 2.7500 1.728250 28.46
2 -135.9000 1.2500
* 3 19.9530 1.9500 1.582760 30.34
4 3.9310 1.6000
5 0.0000 0.5000 (Aperture stop S)
6 -22.6500 5.2000 1.728250 28.46
7 13.6000 6.5000 1.618000 63.37
8 -7.5500 0.7000
* 9 15.7960 5.5000 1.532700 56.19
10 -34.9160 2.5000
11 0.0000 11.0000 1.516800 64.11
12 0.0000 0.7000
[Aspherical data]
3rd surface κ = -5.07580, A4 = -1.20140E-04, A6 = -1.48220E-05
9th surface κ = 0.99160, A4 = -1.13120E-04, A6 = -4.50900E-07
[Various data]
f = 10.716
NA = 0.20
ω = 25.78 °
β = 0.0192
f1 = 18.444
[Conditional expression]
T34 = 11.70
T = 25.95
Conditional expression (1) f1 / f = 1.70
Conditional expression (2) | f1 / f | = 1.70
Conditional expression (3) R3 / f = -2.11
Conditional expression (4) T34 / T = 0.45
Conditional expression (5) nd2 = 1.58
Conditional expression (6) νd2 = 30.3
Conditional expression (7) nd5 = 1.53
Conditional expression (8) νd5 = 56.2

  From the table of specifications shown in Table 3, it can be seen that the lens system PL3 according to the third example satisfies all the conditional expressions (1) to (8).

  FIG. 6 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion aberration diagram, chromatic aberration diagram of magnification, and coma aberration diagram) of the third example. As is apparent from each aberration diagram, although the lens system PL3 according to the third example has a short total length of the optical system and a small number of lenses, various aberrations are well corrected and high optical performance is achieved. It is clear that it has performance.

(Fourth embodiment)
A lens system according to the fourth example will be described with reference to FIGS. 7 and 8 and Table 4. FIG. As shown in FIG. 7, the lens system PL4 according to the fourth example includes a first lens L1 having a positive refractive power and a second lens having a negative refractive power arranged in order from the projection side along the optical axis. It has a lens L2, a third lens L3 having a negative refractive power, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a positive refractive power.

  The first lens L1 is a biconvex positive lens whose projection side has a stronger refractive index than the object side. The second lens L2 is a negative meniscus lens in which an aspherical surface is formed on the lens surface on the projection side, and the projection surface has a convex surface facing the projection side having a weak refractive index compared to the object side. The third lens L3 is a biconcave negative lens whose projection side has a lower refractive index than the object side. The fourth lens L4 is a biconvex positive lens having a lower refractive index on the projection side than on the object side. The fifth lens L5 is a biconvex positive lens in which an aspherical surface is formed on the lens surface on the projection side. The third lens L3 and the fourth lens L4 are bonded to form a cemented lens L34 having a positive refractive power as a whole. An aperture stop S is disposed between the second lens L2 and the third lens L3.

  In addition, on the object side of the fifth lens L5, a parallel flat glass GB corresponding to a color synthesis prism and an image display element LCD such as a liquid crystal panel are arranged.

  Table 4 shows a table of specifications in the fourth embodiment. In addition, the surface numbers 1-12 in Table 4 respond | correspond to the surfaces 1-12 shown in FIG. In the fourth embodiment, each of the third and ninth lens surfaces is aspherical.

(Table 4)
[Lens data]
Surface number r d nd νd
1 23.5000 2.2000 1.755199 27.15
2 -110.0000 0.2500
* 3 10.3300 3.9500 1.607100 26.63
4 3.8000 1.2000
5 0.0000 0.2000 (Aperture stop S)
6 -18.0660 5.0000 1.728250 28.46
7 12.2490 6.2500 1.618000 63.37
8 -7.5200 0.2000
* 9 21.5900 4.1000 1.532700 56.19
10 -15.9500 2.5000
11 0.0000 11.0000 1.516800 64.11
12 0.0000 0.7000
[Aspherical data]
3rd surface κ = 0.88900, A4 = -2.36470E-04, A6 = -2.59200E-06
9th surface κ = 4.45620, A4 = -1.31360E-04, A6 = -7.94810E-07
[Various data]
f = 10.815
NA = 0.20
ω = 25.88 °
β = 0.0194
f1 = 25.823
[Conditional expression]
T34 = 11.25
T = 23.35
Conditional expression (1) f1 / f = 2.39
Conditional expression (3) R3 / f = -1.67
Conditional expression (4) T34 / T = 0.48
Conditional expression (5) nd2 = 1.61
Conditional expression (6) νd2 = 26.6
Conditional expression (7) nd5 = 1.53
Conditional expression (8) νd5 = 56.2

  From the table of specifications shown in Table 4, it can be seen that the lens system PL4 according to the fourth example satisfies all the conditional expressions (1) and (3) to (8).

  FIG. 8 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion aberration diagram, chromatic aberration diagram of magnification, and coma aberration diagram) of the fourth example. As is apparent from the respective aberration diagrams, the lens system PL4 according to the fourth example has various aberrations corrected satisfactorily even though the total length of the optical system is short and the number of lenses is small. It is clear that it has performance.

  In the above-described embodiment, the following description can be appropriately adopted as long as the optical performance is not impaired.

  In the above-described embodiments, the five-lens configuration is shown as the lens system, but the present invention can also be applied to other configurations of the number of lenses such as six or seven. Further, a configuration in which a lens or a lens component is added to the most object side, or a configuration in which a lens or a lens component is added to the most image side may be used.

  Alternatively, a single lens or a plurality of lenses, a partial lens, or an entire lens system may be moved in the optical axis direction so as to focus from an object at infinity to a near object. The focusing lens can be applied to autofocus, and is also suitable for driving a motor for autofocus (such as an ultrasonic motor). In particular, the entire lens system is preferably a focusing lens.

  In addition, the lens or the partial lens is moved so as to have a component in the direction perpendicular to the optical axis, or rotated (swinged) in the in-plane direction including the optical axis to correct image blur caused by camera shake. An anti-vibration lens may be used. In particular, it is preferable to use the third and fourth lenses L3 and L4 (junction lens L34) as vibration-proof lenses.

  The second and fifth lenses L2 and L5 are preferably plastic lenses, but one or both of them may be formed of glass lenses.

  Further, the lens surface may be formed as a spherical surface, a flat surface, or an aspherical surface. It is preferable that the lens surface is a spherical surface or a flat surface because lens processing and assembly adjustment are facilitated, and deterioration of optical performance due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. On the other hand, when the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite type non-spherical surface made of resin on the glass surface. Any aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  Each lens surface may be provided with an antireflection film having a high transmittance in a wide wavelength region in order to reduce flare and ghost and achieve high optical performance with high contrast.

  In addition, in order to make this invention intelligible, although demonstrated with the component requirement of embodiment, it cannot be overemphasized that this invention is not limited to this.

PL lens system 1 Projector (optical equipment)
L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L34 Joint lens S Aperture stop GB Parallel plane glass PBS Polarization beam splitter LCD Image display element

Claims (13)

In the configuration having five lenses of the first to fifth lenses arranged in order from the projection side along the optical axis,
The third lens and the fourth lens are bonded together to form a cemented lens;
The first lens is a biconvex lens;
When the focal length of the first lens is f1, and the focal length of the entire lens system is f, the following expression 1.65 <f1 / f <2.40
A lens system that satisfies the following conditions. In the configuration having five lenses of the first to fifth lenses arranged in order from the projection side along the optical axis,
The third lens and the fourth lens are bonded together to form a cemented lens;
When the focal length of the first lens is f1, and the focal length of the entire lens system is f, the following expression 1.65 <| f1 / f | <2.05
A lens system that satisfies the following conditions. When the curvature radius of the lens surface on the projection side of the third lens is R3, the following formula −2.45 <R3 / f <−1.60
The lens system according to claim 1, wherein the following condition is satisfied. The distance on the optical axis from the lens surface on the projection side of the third lens to the lens surface on the object side of the fourth lens is T34, and from the lens surface on the most projection side to the lens surface on the most object side in the entire lens system. When the distance on the optical axis is T, the following expression 0.30 <T34 / T <0.52
The lens system according to claim 1, wherein the following condition is satisfied. When the refractive index for the d-line of the second lens is nd2, the following formula 1.56 <nd2 <1.62
The lens system according to claim 1, wherein the following condition is satisfied. When the Abbe number with respect to the d-line of the second lens is νd2, the following formula 25.0 <νd2 <35.0
The lens system according to claim 1, wherein the lens system satisfies the following condition. When the refractive index for the d-line of the fifth lens is nd5, the following formula 1.52 <nd5 <1.55
The lens system according to claim 1, wherein the following condition is satisfied. When the Abbe number of the fifth lens with respect to the d-line is νd5, the following expression 54.0 <νd5 <58.0
The lens system according to claim 1, wherein the following condition is satisfied.   The lens system according to any one of claims 1 to 8, wherein at least one of the second lens and the fifth lens is a plastic lens.   The lens system according to any one of claims 1 to 9, wherein at least one of the second lens and the fifth lens is an aspherical lens.   The lens system according to any one of claims 1 to 10, wherein an aperture stop is provided between the second lens and the third lens.   The lens system according to claim 2, wherein the first lens has a positive refractive power.   An optical apparatus comprising the lens system according to any one of claims 1 to 12.

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