JP2007178826A - Attachment lens and optical system having same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an attachment lens constituted of a small number of lenses and capable of reducing the distortion aberration of the entire lens system when it is attachably/detachably attached to the enlargement conjugate side of a main lens system, and to obtain an optical system having the same. <P>SOLUTION: The attachment lens attachably/detachably attached to the enlargement conjugate side of the main lens system comprises a positive lens, a negative lens, a negative lens and a positive lens in order from the enlargement conjugate side to a reduction conjugate side, and satisfies a condition of -0.002(1/mm)<ϕ<0.002(1/mm) when refractive power is defined as ϕ(1/mm). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is detachably mounted on an enlargement conjugate side of a projection optical system used in an imaging optical system used in an imaging device such as a camera and a projector that projects light from an image display element such as a liquid crystal panel onto a screen or the like. The present invention relates to an attachment lens and an optical system having the same.

  2. Description of the Related Art Conventionally, various liquid crystal projectors (image projection apparatuses) for enlarging and projecting image information based on a display surface such as a liquid crystal display element on a screen have been proposed.

  Since this liquid crystal projector can project image information of a personal computer or the like on a large screen, it is widely used for conferences and presentations.

  Projection optical systems used in liquid crystal projectors require optical systems with high zoom magnification that can change the projection angle of view in various ways in order to realize projection in conference rooms with various shapes. ing.

  Conventionally, in a projection optical system, an attachment lens is detachably mounted on the magnification conjugate side of a main lens system (projection lens) (Patent Documents 1 and 2). This shifts the focal length of the entire system and changes the projection angle of view. Such an attachment lens is said to be a wide converter lens or a teleconversion lens.

By using an attachment lens such as a wide converter lens or a teleconverter lens, it is possible to easily change the projection angle of view and enlarge or reduce the image information on the screen for projection.
JP 2001-272600 A JP 2002-107619 A

  In order to change the projection angle of view, when an attachment lens is mounted on the magnification conjugate side of the main lens system (projection lens), it is important not to deteriorate the imaging performance of the main lens system. For example, when the main lens system has distortion among various aberrations, it is important not to deteriorate the distortion so that the projected image is distorted at the contour portion and is not unsightly.

  In addition, it is important that the attachment lens is small in size and light in weight so that it can be easily attached to the main lens system.

  The teleconverter lens disclosed in Patent Document 1 and the wide converter lens disclosed in Patent Document 2 have as many as six or more lenses and are complex, and the entire lens system tends to be large.

  In addition, there is a tendency that a large amount of lateral chromatic aberration and distortion are left even when mounted on a projection main lens system.

  If there is a lot of distortion among the various aberrations in the projection optical system used for image projection devices such as liquid crystal projectors, the contour will be curved (pound or barrel) when image information is projected on the screen. The image will bend and become very unsightly.

  However, many projection optical systems are so-called retrofocus types, which are composed of a negative refractive power lens group, an aperture stop, and a positive refractive power lens group in order from the magnification conjugate side (screen) to the reduction conjugate side (image display element side). Often consists of a lens system.

  A retro-focus type lens system tends to generate a lot of pincushion distortion when projected onto a screen.

  In general, it is very difficult to correct the distortion at this time with a projection lens.

  For this reason, when an attachment lens is mounted on the magnification conjugate side of the main lens system, it is desirable to correct the distortion of the main lens system with this attachment lens.

  However, it is very difficult to correct even the distortion of the main lens system while changing the projection angle of view of the main lens system with an attachment lens having a simple lens configuration.

  An object of the present invention is to provide an attachment lens capable of reducing distortion of the entire lens system and an optical system having the same when it is detachably mounted on the magnification conjugate side of the main lens system with a small number of lenses. To do.

The attachment lens of the present invention is an attachment lens that is detachably attached to the enlargement conjugate side of the main lens system, and comprises a positive lens, a negative lens, a negative lens, and a positive lens in order from the enlargement conjugate side to the reduction conjugate side. When the refractive power is φ (1 / mm) −0.002 (1 / mm) <φ <0.002 (1 / mm)
It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to obtain an attachment lens that can reduce distortion of the entire lens system when it is detachably mounted on the magnification conjugate side of the main lens system.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an attachment lens of the present invention and a projection optical system when the attachment lens is mounted on a main lens system (projection optical system of an image projection apparatus such as a liquid crystal projector) and an image projection apparatus using the projection optical system will be described below. To do.

  FIG. 1 is a lens cross-sectional view when the attachment lens AL of Example 1 of the present invention is mounted on the enlargement conjugate side of the main lens system (master lens) MS. FIG. 2 is an aberration diagram of the main lens system MS.

  3A and 3B are a lens cross-sectional view of the attachment lens AL of Example 1 of the present invention and aberration diagrams when the attachment lens AL of Example 1 is mounted on the magnification conjugate side of the main lens system MS. is there.

  4A and 4B are a lens cross-sectional view of the attachment lens AL of Example 2 of the present invention and when the attachment lens AL of Example 2 is mounted on the magnification conjugate side of the main lens system MS shown in FIG. FIG.

  5A and 5B show a lens cross-sectional view of the attachment lens AL of Example 3 of the present invention and when the attachment lens AL of Example 3 is mounted on the magnification conjugate side of the main lens system MS shown in FIG. FIG.

  6A and 6B show a lens cross-sectional view of the attachment lens AL of Example 4 of the present invention and when the attachment lens AL of Example 4 is mounted on the magnification conjugate side of the main lens system MS shown in FIG. FIG.

  7A and 7B are explanatory diagrams relating to distortion aberration when an image display element is projected onto a projection surface (screen surface) by the image projection apparatus of the present invention.

  FIG. 8 is a schematic view of a main part of an image projection apparatus (color liquid crystal projector) according to the present invention.

  The image projection apparatus in FIG. 1 shows a state where an original image (projected image) of the LCD is enlarged and projected on the screen surface S using the projection optical system PL.

  S is a screen surface (projection surface, projection surface), and LCD is an original image (projection image) such as a liquid crystal panel (liquid crystal display element). The screen surface S and the original image LCD are in a conjugate relationship or a substantially conjugate relationship.

  In general, the screen surface S corresponds to the enlargement side (front) at the conjugate point with the longer distance (enlarged conjugate point), and the original image LCD corresponds to the reduction side (rear) at the conjugate point with the shorter distance (reduced conjugate point). is doing.

  Note that the projection optical system PL can also be used as an imaging optical system that captures an image. At this time, the screen surface S side is the object side, and the original image LCD side is the image side on which the image sensor is arranged.

  GB is a glass block (prism) provided for optical design corresponding to a color synthesis prism, a polarizing filter, a color filter, and the like.

  The projection optical system PL is mounted on a liquid crystal projector main body (not shown) via a connection member (not shown). The liquid crystal display element LCD side after the glass block GB is included in the projector body.

  In the aberration diagrams, F is the F number. IMG HT is the image height of the LCD on the liquid crystal display element side. S is a sagittal image plane, and M is a meridional image plane.

The attachment lens AL of each embodiment is detachably mounted on the enlargement conjugate side of the main lens system MS. The attachment lens AL includes a positive lens, a negative lens, a negative lens, and a positive lens in order from the magnification conjugate side to the reduction conjugate side. When the refractive power of the attachment lens AL is φ (1 / mm) −0.002 (1 / mm) <φ <0.002 (1 / mm) (1)
Is satisfied.

  Conditional expression (1) relates to the refractive power of the attachment lens AL. If the refractive power of the attachment lens AL exceeds the range of the conditional expression (1), the basic lens specifications such as the back focus of the main lens system when attached to the main lens system are changed, which is not preferable.

Conditional expression (1) is more preferably set as follows.
−0.001 (1 / mm) <φ <0.0013 (1 / mm) (1a)
The specific lens configuration of the attachment lens AL is as follows.

  In order from the magnification conjugate side to the reduction conjugate side, both lens surfaces are convex positive lenses, both lens surfaces are concave negative lenses, the magnification conjugate side surfaces are convex and meniscus negative lenses, and the magnification conjugate side surfaces are Consists of a convex meniscus positive lens.

  This reduces the occurrence of various aberrations including distortion of the entire lens system when it is mounted on the main lens system, regardless of the number of four lenses.

  The attachment lens AL of each embodiment is arranged such that the positive lens is located closest to the magnification conjugate side so that it is far from the pupil (aperture position) when attached to the magnification conjugate side of the main lens system MS. As a result, negative distortion occurring in the main lens, which is a retrofocus projection lens, is efficiently corrected.

N _p> N _n and the refractive index N _p of the material of the first positive _lens, the refractive index of the material of the second negative lens and a N _n which is disposed closest to the enlargement conjugate side of the attachment lens AL
It is said.

  The surface on the reduction conjugate side of the first positive lens has a convex shape.

  As a result, distortion of the entire lens system when mounted on the main lens system is efficiently corrected.

  The first positive lens and the second negative lens arranged on the most magnification conjugate side are preferably bonded to each other. According to this, chromatic aberration can be corrected efficiently.

When the focal length of the main lens system MS is F, and the focal length when the attachment lens AL is attached to the main lens system MS is f,
0.9 <f / F <1.2 (2)
Is satisfied.

  According to this, the focal length of the entire lens system can be shifted to the wide side and the tele side. Exceeding the range of conditional expression (2) is not preferable because the lens configuration of the attachment lens becomes complicated to correct various aberrations.

  Conditional expression (2) is more preferably set as follows.

0.95 <f / F <1.15 (2a)
As described above, when the attachment lens of each embodiment is applied to a projection lens such as a projector, an image with little distortion is obtained for an image projected on a screen.

  Next, the features of each embodiment will be described sequentially.

  A main lens system MS shown in FIG. 1 is disposed in a projector and projects light from the liquid crystal display element LCD onto a projection surface S such as a screen. The attachment lens AL of each embodiment shifts the focal length of the main lens system MS, and particularly corrects distortion aberration of the main lens system MS.

  The attachment lens AL of Example 1 is a lens unit that can be attached to and detached from the main lens system MS as shown in FIG. FIG. 3 shows various aberrations of the projection optical system in which the main lens system MS and the attachment lens AL are combined when the attachment lens AL of Example 1 is mounted.

  As can be seen from FIG. 3, only spherical aberration and astigmatism are greatly reduced in spite of the fact that they do not change much compared to various aberrations of only the main lens system MS shown in FIG. I understand.

  FIG. 7 shows a comparison of distortion on the screen S when only the main lens system MS and the attachment lens AL are mounted in the first embodiment. As shown in FIG. 7A, in the case of only the main lens system, an ideal rectangular frame bends due to distortion and looks like a pincushion shape. On the other hand, when the attachment AL of Example 1 is attached to the main lens system MS, it can be seen that a projection pattern close to a substantially ideal rectangular frame can be realized as shown in FIG.

  Here, the attachment lens AL of Example 1 has a four-lens configuration in which positive, negative, negative, and positive lenses are arranged in this order from the magnification conjugate side to the reduction conjugate side. In particular, by making the surface on the reduction conjugate side of the first positive lens convex, the aforementioned distortion is efficiently reduced.

  Specifically, a cemented lens obtained by cementing a positive lens whose convex surfaces are convex and a negative lens whose concave surfaces are concave, a negative meniscus lens whose convex surface is convex, and a convex conjugate surface Is composed of four groups of four meniscus positive lenses having a convex shape.

  The numerical values of conditional expressions (1) and (2) of Example 1 are as follows.

Conditional expression (1) φ = −0.00001
(2) f / F = 1.068

  Example 2 shown in FIG. 4 is different from Example 1 in part of the lens configuration of the attachment lens AL. The attachment lens AL of Example 2 is composed of four lenses of positive, negative, negative, and positive lenses in order from the magnification conjugate side to the reduction conjugate side, and the first positive lens and the second negative lens are mutually connected. It is configured independently. Similarly to the first embodiment, the distortion aberration is efficiently corrected by making the surface on the reduction conjugate side of the first positive lens convex.

  The lens shape of each lens is the same as in the first embodiment.

  The numerical values of conditional expressions (1) and (2) in Example 2 are as follows.

Conditional expression (1) φ = +0.000069
(2) f / F = 1.089

  Example 3 shown in FIG. 5 is different from Example 1 in part of the lens configuration of the attachment lens AL. The attachment lens AL of Example 3 is composed of four positive, negative, negative, and positive lenses in order from the magnification conjugate side to the reduction conjugate side. The first positive lens and the second negative lens are mutually connected. It is configured independently. Similarly to the first embodiment, the distortion aberration is efficiently corrected by making the surface on the reduction conjugate side of the first positive lens convex. The lens shape of each lens is the same as in the first embodiment.

  The numerical values of conditional expressions (1) and (2) in Example 3 are as follows.

Conditional expression (1) φ = +0.000213
(2) f / F = 1.112

  Example 4 shown in FIG. 6 is different from Example 1 in part of the lens configuration of the attachment lens AL. The attachment lens AL of Example 4 is composed of four positive, negative, negative, and positive lenses in order from the magnification conjugate side to the reduction conjugate side. The first positive lens and the second negative lens are mutually connected. It is configured independently.

  Similarly to the first embodiment, the distortion aberration is efficiently corrected by making the surface on the reduction conjugate side of the first positive lens convex.

  The lens shape of each lens is the same as in the first embodiment. The numerical values of conditional expressions (1) and (2) in Example 4 are as follows.

Conditional expression (1) φ = + 0.00115
(2) f / F = 0.975
FIG. 8 is a schematic view of the essential portions of Embodiment 5 in which the projection optical system PL of the present invention is applied to a three-plate color liquid crystal projector (projection apparatus).

  In the figure, 100 is an illumination system, MS is a projection lens, and AL is an attachment lens that can be attached to and detached from the projection lens MS. The illumination system 100 illuminates liquid crystal panels PB, PR, and PG, which will be described later, by separating light from the white light source LS into blue, green, and red color light using dichroic mirrors 102 and 103, respectively.

  Reference numerals 113 and 114 denote first and second field lenses that guide an image based on the liquid crystal panels PB, PR, and PG to the projection lens MS through the dichroic prism DCP.

  Blue light (B light) is transmitted by the dichroic mirror 102, and green light (G light) and red light (R light) are reflected from the light beam from the light source LS.

  Of the G light and R light from the dichroic mirror 102, the R light is reflected by the dichroic mirror 103 and the G light is transmitted. The B light transmitted through the dichroic mirror 102 illuminates the liquid crystal panel PB for B light via the mirror 104 and the condenser lens CB. The R light reflected by the dichroic mirrors 102 and 103 illuminates the liquid crystal panel PR for R light via the condenser lens CR.

  The G light reflected by the dichroic mirror 102 and transmitted through the dichroic mirror 103 illuminates the liquid crystal panel PG for G light via the condenser lens CG.

  The light beam from the liquid crystal panel PB for B light is transmitted through the dichroic mirror 105 that transmits B light and reflects R light. Next, the light is incident on a dichroic prism DCP in which two prisms 121 and 122 each having a dichroic film formed on a joint surface for color synthesis are joined via a first field lens 113.

  The light beam from the R light liquid crystal panel PR is reflected by the dichroic mirror 105 and enters the dichroic prism DCP via the first field lens 113. The light beam from the G light liquid crystal panel PG is reflected by the mirror 106 and enters the dichroic prism DCP via the second field lens 114.

  Images based on the liquid crystal panels PB, PR, and PG are synthesized on the dichroic surface DCPa of the dichroic prism DCP, and the synthesized image is enlarged and projected on the screen S via the projection lens MS and the attachment lens CL.

  Next, Numerical Examples 1 to 4 corresponding to Embodiments 1 to 4 of the attachment lens and Numerical Examples of the main lens system MS to which the attachment lens is attached will be shown.

  In each numerical example, i indicates the order of the optical surfaces from the magnification conjugate side, R is the radius of curvature of the optical surface, d is the distance between the i-th surface and the (i + 1) -th surface, and n and ν are d-lines, respectively. Represents the refractive index and Abbe number of the material of the optical member.

  Further, in the numerical example of the main lens system, the four surfaces on the reduction conjugate side are surfaces constituting a glass block provided in design corresponding to a color synthesis prism or the like.

  In the aspherical shape, the incident height of the incident light beam from the surface vertex of the surface where the Z aspherical surface is set in the optical axis direction to the direction perpendicular to the optical axis of the surface is h.

  Also, the reciprocal of the surface vertex radius of curvature is c, the conic constant is K, the second order aspheric coefficient is A, the fourth order aspheric coefficient is B, the sixth order aspheric coefficient is C, and the eighth order aspheric coefficient is D, E is the 10th-order aspheric coefficient.

  At this time,

It is an axisymmetric aspherical shape represented by Further, the display of “ ^ez ” means “10 ^−Z ”.

(Main lens system)
Ri di ni νi
1 48.955 2.30 1.812 25.4
2 21.197 6.79
3 (Aspherical surface) 3.10 1.532 55.8
4 (Aspherical) 11.30
5 -27.285 1.75 1.489 70.2
6 -1003.608 1.50
7 -230.265 4.45 1.839 37.2
8 -56.002 6.41
9 139.390 4.80 1.839 37.2
10 -108.108 22.55
11 52.141 4.30 1.607 38.0
12 382.739 34.81
13 -39.575 1.50 1.761 27.5
14 -320.549 3.00
15 -319.941 1.50 1.839 37.2
16 34.971 5.70 1.489 70.2
17 -101.852 0.15
18 63.766 7.70 1.489 70.2
19 -43.346 0.17
20 (Aspherical) 4.15 1.532 55.8
21 (Aspherical) 17.17
22 56.204 4.90 1.489 70.2
23 -451.444 1.45
24 ∞ 55.00 1.849 24.6
25 ∞ 0.00
26 ∞ 3.80 1.518 64.1
27 ∞

Aspheric data
3 c (1 / r) = 2.480e-002 k = -8.653e-001 A = -1.692e-005 B = 8.804e-008
C = -3.276e-010 D = 8.716e-013 E = -1.051e-015
4 c (1 / r) = 4.077e-002 k = -4.329e + 000 A = 9.732e-008 B = 1.985e-008
C = -2.454e-010 D = 8.708e-013 E = -1.412e-015
20 c (1 / r) =-8.859e-003 k = -6.587e + 001 A = -1.096e-005 B = 3.458e-008
C = -1.449e-010 D = 4.494e-013 E = -4.341e-016
21 c (1 / r) =-1.814e-002 k = -7.913e + 000 A = -9.268e-006 B = 2.295e-008
C = -9.433e-011 D = 2.938e-013 E = -2.508e-016

Numerical example 1
Ri di ni νi
1 85.656 11.18 1.575 57.7
2 -220.616 3.45 1.518 64.1
3 59.300 4.04
4 66.291 2.80 1.812 25.4
5 44.011 4.76
6 43.123 5.09 1.624 36.3
7 82.312 10.00


Numerical example 2
RI di ni νi
1 103.840 9.11 1.524 59.8
2 -419.339 3.00
3 -395.439 3.30 1.489 70.2
4 87.350 5.00
5 106.854 3.50 1.812 25.4
6 64.989 2.89
7 65.970 4.89 1.839 37.2
8 106.121 8.00


Numerical Example 3
RI di ni νi
1 83.390 13.89 1.520 58.9
2 -255.561 0.56
3 -233.669 4.20 1.489 70.2
4 58.470 4.92
5 197.283 3.74 1.812 25.4
6 72.288 1.52
7 64.423 13.00 1.839 37.2
8 194.548 8.00


Numerical Example 4
Ri di ni νi
1 103.956 8.88 1.520 52.4
2 -957.458 0.19
3 -1449.867 3.30 1.489 70.2
4 49.519 12.22
5 108.371 7.00 1.812 25.4
6 47.264 6.72
7 45.619 7.11 1.839 37.2
8 176.332 8.00

Sectional drawing of the lens of the optical system which has an attachment lens of Example 1 Aberration diagram of the main lens system of FIG. Lens sectional view and aberration diagram of the attachment lens of Example 1 Lens sectional view and aberration diagram of the attachment lens of Example 2 Lens sectional view and aberration diagram of the attachment lens of Example 3 Lens sectional view and aberration diagram of the attachment lens of Example 4 Explanatory drawing of how distortion is reduced Schematic diagram of the projection apparatus of Embodiment 5

Explanation of symbols

LCD Liquid crystal display (image plane)
GB glass block (color synthesis prism)
S Sagittal image plane fall M Meridional image plane fall AL Attachment lens MS Main lens system PL Projection optical system S Screen

Claims (8)

An attachment lens that is detachably attached to the magnification conjugate side of the main lens system, and is composed of a positive lens, a negative lens, a negative lens, and a positive lens in order from the magnification conjugate side to the reduction conjugate side, and has a refractive power of φ (1 / Mm) −0.002 (1 / mm) <φ <0.002 (1 / mm)
An attachment lens characterized by satisfying the following conditions:   2. The attachment lens according to claim 1, wherein the positive lens on the most conjugate side has a convex surface on the reduction conjugate side. When the refractive index of the first positive lens material is N _p and the refractive index of the second negative lens material is N _n in order from the magnification conjugate side to the reduction conjugate side, N _p > N _n
The attachment lens according to claim 1 or 2, wherein:   The attachment lens according to claim 1, 2, or 3, wherein the first positive lens and the second negative lens are bonded in order from the magnification conjugate side to the reduction conjugate side.   The attachment lens is, in order from the magnification conjugate side to the reduction conjugate side, both lens surfaces are convex positive lenses, both lens surfaces are concave negative lenses, the magnification conjugate side surfaces are convex, meniscus negative lenses, and magnification The attachment lens according to any one of claims 1 to 4, wherein the conjugate lens is a positive meniscus lens having a convex surface.   An attachment lens that is detachably attached to the enlargement conjugate side of the main lens system, and consists of a positive lens, a negative lens, a negative lens, and a positive lens in order from the enlargement conjugate side to the reduction conjugate side. An attachment lens having a function of correcting aberration. An optical system in which the attachment lens according to any one of claims 1 to 6 is mounted on a magnification conjugate side of the main lens system, wherein the focal length of the main lens system is F, and the attachment lens is mounted on the main lens system. Where f is the focal length
0.9 <f / F <1.2
An optical system characterized by satisfying the following conditions.   An image projection apparatus, wherein image information formed by an image display element is projected onto a screen by the optical system according to claim 7.