JP5507239B2 - Projection optical system - Google Patents

Description

  The present invention relates to a projection optical system.

  2. Description of the Related Art Conventionally, a so-called retrofocus type optical system that includes a negative first lens group and a positive second lens group in order from the long conjugate side is known. Since this retrofocus type optical system can be easily widened, for example, it is widely used for projection lenses of projectors (see, for example, Patent Documents 1 to 3).

JP 2001-91827 A JP 2003-337283 A JP 2006-113300 A

However, the conventional projection optical system as described above has the following problems.
In the techniques described in Patent Documents 1 to 3, there is a problem that the value of the F number cannot be reduced too much. For example, Patent Document 1 describes a projection lens with an F number of about 3.0 to about 2.8 centering on 3.0. Patent Document 2 describes a projection zoom lens having an F number of 1.7 at the wide-angle end. Patent Document 3 describes a projection zoom lens having an F number of 2.4 at the wide-angle end.
For this reason, there is a strong demand for a projection optical system capable of further increasing the diameter to increase the illuminance on the projection surface.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a projection optical system that has a small F number and a wide projection angle and can obtain good optical performance.

In order to solve the above problems, the projection optical system of the present invention, as the lens group, from a long conjugate side in this order, a second lens group having a first lens group and positive refractive power having a negative refractive power a composed projection optical system, the first lens group includes, in order from a long conjugate side, a positive lens, at least three negative lenses, positive lens refractive index is composed of greater than 1.9 glass material, and the long conjugate side A negative meniscus lens having a concave surface is arranged, and the second lens group includes, in order from the long conjugate side, a long conjugate side lens group having a positive refractive power, a diaphragm , and a short conjugate having a positive refractive power. side lens group is configured by disposing the short conjugate side lens group, the negative lens unit having a negative refractive power and having at least one aspheric surface is adjacent to the short conjugate side to the diaphragm structure which is located To.
According to the present invention, the negative lens unit having at least one aspherical surface on the short conjugate side with respect to the stop and having a negative refractive power is disposed adjacently, thereby suppressing the influence of aberration due to off-axis rays. In addition, positive spherical aberration can be corrected.

  According to the projection optical system of the present invention, positive spherical aberration can be corrected while suppressing the influence of aberration caused by off-axis rays, so that good optical performance can be obtained while having a small F number and a wide projection angle. There is an effect that is.

It is sectional drawing containing the optical axis which shows the structure of the projection optical system which concerns on embodiment of this invention. It is sectional drawing containing the optical axis which shows the structure of the projection optical system which concerns on the modification of embodiment of this invention. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of a numerical example of the projection optical system according to the embodiment of the present invention. FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of a numerical example of the projection optical system according to a modification of the embodiment of the present invention.

Hereinafter, a projection optical system according to an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view including an optical axis showing a configuration of a projection optical system according to an embodiment of the present invention.

  As shown in FIG. 1, the projection optical system 100 of the present embodiment is a color that combines a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a plurality of wavelength lights. A color synthesizing element group PR including the synthesizing prism 13 is arranged in this order, and an image of the element display surface I arranged at a fixed position near the color synthesizing element group PR is separated from the first lens group G1. This is an optical system for enlarging and projecting at a predetermined optical magnification onto a screen (not shown), which is a projection surface disposed on the screen. In the projection optical system 100, the lens optical axes of the lenses constituting the first lens group G1 and the second lens group G2 are aligned on the same axis, and the optical axes of the lens and the optical axis of the projection optical system 100 coincide with each other. Has been.

  In the following, when referring to the positional relationship in the direction along the optical axis of the projection optical system 100, the side closer to the projection surface (the left side in FIG. 1) is the “long conjugate side” and the side closer to the display element surface I (see FIG. The right side of FIG. 1 is referred to as the “short conjugate side”. The position of the lens or lens surface in the lens group is “the longest conjugate side (short conjugate side)” is a longer conjugate side (short conjugate side) than the positions of all other lenses or lens surfaces in the lens group. Means to be located in

As the display element surface I, for example, a display surface of a transmissive or reflective display element in which spatial modulation elements arranged two-dimensionally are driven to be modulated by an appropriate image signal can be employed.
As an example of the transmissive display element, a transmissive liquid crystal modulation element can be given. Examples of reflective display elements include, for example, a digital micromirror device (DMD) in which movable micromirrors are arranged and a reflective liquid crystal panel (LCOS, Liquid Crystal On Silicon). A display element can be mentioned.
The projection optical system 100 includes the color synthesis prism 13 to synthesize light from a plurality of display element surfaces I, for example, three display element surfaces I corresponding to the three primary colors of light, and project the light onto the projection surface. In FIG. 1, only one display element surface I is displayed, and the other display element surfaces I are not shown.

The first lens group G1 includes, in order from the long conjugate side, a lens 1 consisting of a biconvex lens, a lens 2 consisting of a negative meniscus lens having a convex surface facing the long conjugate side, and a lens consisting of a negative meniscus lens having a convex surface facing the long conjugate side. 3, a cemented lens 4 and a lens 5 composed of a negative meniscus lens having a concave surface facing the long conjugate side are disposed, and are configured to have negative refractive power as a whole.
The cemented lens 4 includes a negative lens 4A that is a biconcave lens and a positive lens 4B that is a positive meniscus lens having a convex surface facing the long conjugate side, which are joined in this order from the long conjugate side. Has refractive power.
The positive lens 4B of the present embodiment is made of a glass material having a refractive index larger than 1.9 in order to increase the refractive power of the cemented lens 4.

With such a configuration, the refractive powers of all six lenses of the first lens group G1 of the present embodiment are positive, negative, negative, negative, positive, and negative in order from the long conjugate side. In the present embodiment, the lens 1 is made of a glass material having a refractive index of 1.9 or less.
As described above, the first lens group G1 includes two positive lenses and four negative lenses. The two positive lenses are arranged in such a positional relationship that the positive lens 4B, which is a positive lens made of a glass material having a refractive index greater than 1.9, is on the shorter conjugate side, that is, the side closer to the second lens group G2. ing.

In the first lens group G1 of the present embodiment, the focal length of the entire projection optical system 100 (however, the focal length at a wavelength of 587.56 nm; the same applies to the following focal lengths) is defined as the focal length f. when the composite focal length of the group G1 to the focal length f _1, it is preferable to satisfy the following condition (1).

0.85 <| f ₁ | / f <1.3 (1)

The second lens group G2 includes, in order from the long conjugate side, a lens 6 consisting of a biconvex lens, a lens 7 consisting of a positive meniscus lens having a convex surface facing the long conjugate side, a diaphragm 8, and a concave surface on which the short conjugate side is aspheric. An aspherical lens 9 made of a concave lens, a cemented lens 10, a lens 11 made of a positive meniscus lens having a concave surface facing the long conjugate side, and a lens 12 made of a biconvex lens are arranged so as to have a positive refractive power as a whole. It has been done.
The cemented lens 10 includes a negative lens 10A, which is a biconcave lens, and a positive lens 10B, which is a biconvex lens, which are cemented in this order from the long conjugate side, and has a negative refractive power as a whole.

With such a configuration, the refractive powers of all seven lenses of the second lens group G2 of the present embodiment are positive, positive, negative, negative, positive, positive, and positive in order from the long conjugate side.
In this embodiment, an aspheric lens 9, which is a single lens having one aspheric surface and having negative refractive power, is provided adjacent to the diaphragm 8 on the short conjugate side.
However, the lens disposed adjacent to the short conjugate side with respect to the stop 8 in the second lens group G2 is not limited to a negative single lens, and may be a negative lens unit. Here, the negative lens unit means a single lens or a lens group that realizes a negative refractive power by a plurality of lens configurations. The negative lens unit may be, for example, a cemented lens in which an appropriate number of lenses are cemented and has negative refractive power as a whole.

In the second lens group G2 of the present embodiment, the lenses 6 and 7, which are two positive lenses, are long conjugate side lens groups which are lens groups having positive refractive power disposed on the long conjugate side with respect to the stop. Is configured.
The aspherical lens 9, the cemented lens 10 composed of the negative lens 10A and the positive lens 10B, and the two lenses 11 and 12, which are positive lenses, are arranged at a short conjugate position with respect to the stop. A short conjugate side lens group which is a lens group having a positive refractive power is configured.

In the second lens group G2 of the present embodiment, when the composite focal length of the second lens group G2 to the focal length f _2, it is preferable to satisfy the following condition (2).

1.2 <f ₂ /f<1.9 (2)

Further, when the focal lengths of the long conjugate side lens group and the short conjugate side lens group of the second lens group G2 are the focal lengths f _2a and f _2b , respectively, it is preferable that the following conditional expression (3) is satisfied. .

0.52 <f _2a / f _2b <0.82 (3)

In the second lens group G2 of the present embodiment, it is preferable that the following conditional expression (4) is satisfied when the focal length of the aspherical lens 9 which is a negative lens unit is a focal length _fnl2 .

2.0 <| f _nl2 | / f <4.0 (4)

  In this embodiment, the color synthesis prism 13 of the color synthesis element group PR is composed of a dichroic prism having a rectangular parallelepiped shape, and is made to enter red light, green light, and blue light incident from directions along the normal lines of three different incident side surfaces. By combining the light, the light can be emitted from a direction along the normal line of the emission side surface 13a different from the incident side surface on which the light is incident. FIG. 1 shows only the incident side surface 13b facing the emission side surface 13a. Since the color synthesis prism 13 does not have refractive power, it is equivalent to a parallel plate.

  In the color composition element group PR, parallel plates 14 are arranged between the color composition prism 13 and the display element surfaces I. The parallel plate 14 is a cover glass or a wavelength filter of the display element. Note that the configuration of the parallel plate 14 differs depending on the display element, and may be omitted depending on circumstances.

Next, the operation of the projection optical system 100 of this embodiment will be described.
In general, when designing an optical system having a large aperture, that is, an optical system having a small F-number, correction of spherical aberration becomes a problem. In the case of a wide-angle lens used in the projection optical system, there is a problem that the aberration of off-axis rays such as curvature of field deteriorates in the conventional projection optical system if correction is made so that spherical aberration is good.
The inventor pays attention to the fact that the lens in the vicinity of the aperture hardly affects the aberration of off-axis rays, and in order from the long conjugate side, the first lens group having negative refractive power and the second lens having positive refractive power. A projection optical system having a lens group, wherein the first lens group includes a plurality of negative lenses and a positive lens made of a glass material having a refractive index greater than 1.9, and the second lens group includes: And a negative lens unit having at least one aspherical surface and having negative refractive power, the negative lens unit being disposed adjacent to the short conjugate side with respect to the stop. The invention of the projection optical system is achieved.

  In the projection optical system 100 of the present embodiment, since the aspherical lens 9 that is a negative lens unit is disposed adjacent to the stop 8 on the short conjugate side, the aspherical lens 9 reduces the aberration of off-axis rays. Positive spherical aberration can be corrected without much influence. In such aberration correction, since the aspherical lens 9 has an aspherical surface, the aberration can be corrected more effectively than the spherical lens.

  The negative lens unit of the second lens group G2 may have a plurality of lens configurations. However, when configured with a single negative lens as in the present embodiment, the second lens unit is compared with a configuration with a plurality of lenses. The group G2 can be further downsized.

Further, if the angle of the optical system is increased, it becomes difficult to correct field curvature and distortion.
Therefore, in the present embodiment, the correction of distortion is facilitated by arranging a plurality of negative lenses in the first lens group G1.
However, if a plurality of negative lenses are arranged, the Petzval sum becomes too large, and it becomes difficult to correct field curvature. Therefore, in this embodiment, the positive lens 4B, which is the shortest conjugate positive lens in the first lens group G1, is made of a glass material having a refractive index greater than 1.9. Thereby, since Petzval sum can be suppressed, curvature of field can be corrected well.
If the positive lenses of the first lens group G1 are all made of a glass material having a refractive index of 1.9 or less, the Petzval sum cannot be suppressed and it becomes difficult to correct field curvature.

In the projection optical system 100 of the present embodiment, the first lens group G1 includes, from the long conjugate side, the lens 1 that is a positive lens, the lenses 2 and 3 that are negative lenses, the negative lens 4A, and the refractive index. Is provided with a positive lens 4B made of a glass material larger than 1.9, the distortion can be easily corrected by three negative lenses. Also, the field curvature can be corrected well.
In the first lens group G1, the number of negative lenses between the lens 1 and the positive lens 4B is preferably at least 3, and may be 4 or more.
In the present embodiment, in the first lens group G1, among the negative lenses disposed between the two positive lenses, the negative lens 4A, which is the shortest conjugate side negative lens, and the positive lens 4B are cemented lenses. 4 is configured. For this reason, it is easy to correct lateral chromatic aberration.
In this embodiment, since the lens 5 which is a negative meniscus lens having a concave surface facing the long conjugate side is arranged on the shortest conjugate side of the first lens group G1, correction of coma becomes easy.

  Further, the second lens group G2 of the present embodiment has a long conjugate side lens group and a short conjugate side lens group with the stop 8 interposed therebetween. The long conjugate side lens group is composed of two positive lenses 6 and 7, and the short conjugate side lens group is composed of an aspherical lens 9, a negative lens 10A and a positive lens 10B constituting a negative lens unit. A cemented lens 10 and lenses 12, 13 which are two positive lenses. For this reason, it becomes easy to correct distortion and curvature of field.

  In addition, aberration correction becomes easier as the number of positive lenses in the long conjugate lens group increases. Therefore, at least two sheets are sufficient, and three or more sheets may be used. Similarly, the larger the number of positive lenses that do not constitute the cemented lens of the short conjugate side lens group, the easier the aberration correction. Therefore, at least two sheets are sufficient, and three or more sheets may be used.

Further, in the projection optical system 100 of the present embodiment, when the conditional expressions (1) and (2) are satisfied, the optical performance and the like can be further improved.
Condition (1) shows a preferred size range of the focal length f ₁ of the first lens group G1 to the focal length f of the entire system of the projection optical system 100.
If | f ₁ | / f is 1.3 or more, it is difficult to reduce the diameter of the front lens.
If | f ₁ | / f is 0.85 or less, it becomes difficult to correct distortion.
Therefore, by satisfying the range of conditional expression (1), the front lens diameter can be reduced to reduce the size of the projection optical system 100, and distortion can be corrected more easily.

Condition (2) illustrates a preferred size range of the focal length f ₂ of the second lens group G2 to the focal length f of the entire system of the projection optical system 100.
If f ₂ / f is 1.9 or more, it is difficult to ensure the back focus.
If | f ₁ | / f is 1.2 or less, it becomes difficult to correct curvature of field.
Therefore, by satisfying the range of the conditional expression (2), it becomes easy to secure the back focus, so that the arrangement of the color synthesis prism 13 and the incorporation into the projection apparatus are facilitated, and the field curvature can be made easier. It becomes possible to correct.

It is desirable that the range of values of | f ₁ | / f and f ₂ / f be narrower within the ranges of the conditional expressions (1) and (2), respectively. For example, | f ₁ | / f is preferably in the range indicated by the following conditional expression (1a), and f ₂ / f is preferably set in the range indicated by the following conditional expression (2a).

1.0 <| f ₁ | / f <1.3 (1a)
1.35 <f ₂ /f<1.7 (2a)

In the projection optical system 100 of the present embodiment, when the conditional expression (3) is satisfied, the optical performance can be further improved.
Conditional expression (3) indicates a preferable size range of the focal length f _2a of the long conjugate lens group with respect to the focal length f _2b of the short conjugate side lens group in the second lens group G2.
If f _2a / f _2b is 0.82 or more, it becomes difficult to correct curvature of field.
If f _2a / f _2b is 0.52 or less, it is difficult to correct spherical aberration.
Therefore, by satisfying the range of conditional expression (3), it becomes easier to correct spherical aberration and curvature of field simultaneously.

The range of the value of f _2a / f _2b is preferably in a narrower range within the range of the conditional expression (3). For example, f _2a / f _2b is preferably in the range indicated by the following conditional expression (3a), and f ₂ / f is preferably set in the range indicated by the following conditional expression (3a).

0.60 <f _2a / f _2b <0.70 (3a)

In the projection optical system 100 of the present embodiment, when the conditional expression (4) is satisfied, the optical performance can be further improved.
Conditional expression (4) indicates a range in which the focal length of the negative lens unit with respect to the focal length f of the entire projection optical system 100 is f _nl2 .
When | f _nl2 | / f is 4.0 or more, it is difficult to correct spherical aberration.
If | f _nl2 | / f is 2.0 or less, it is difficult to reduce sagittal flare of off-axis light flux.
Therefore, by satisfying the range of conditional expression (4), spherical aberration can be corrected more easily, and sagittal flare of off-axis light flux can be reduced more easily.

Note that the range of the value of | f _nl2 | / f is preferably in a narrower range within the range of the conditional expression (4). For example, it is desirable that | f _nl2 | / f be in the range indicated by the following conditional expression (4a).

2.2 <| f _nl2 | / f <3.5 (4a)

  As described above, according to the projection optical system 100 of the present embodiment, positive spherical aberration can be corrected while suppressing the influence of aberration due to off-axis rays, so that a small F number and a wide projection angle of view can be obtained. Good optical performance can be obtained while having it.

Next, a modification of this embodiment will be described.
As shown in FIG. 2, the projection optical system 200 of this modification example is replaced with a first lens group G21 and a second lens instead of the first lens group G1 and the second lens group G2 of the projection optical system 100 of the above embodiment. A group G22 is provided. Hereinafter, a description will be given focusing on differences from the above embodiment.

The first lens group G21 includes a first lens group G1 lens of the above embodiments 1, 2, 3, a cemented lens 4, in place of the lens 5, respectively, lenses 21, 22, 23, a cemented lens 24, lens 2 5 Is provided.
Similarly to the lens 1, the lens 21 is made of a glass material having a refractive index of 1.9 or less, but is different in that it is composed of a positive meniscus lens having a convex surface facing the long conjugate side.
The lenses 22 and 22 are each composed of a negative meniscus lens having a convex surface facing the long conjugate side like the lenses 2 and 3.
The cemented lens 24 includes a negative lens 24A and a positive lens 24B instead of the negative lens 4A and the positive lens 4B of the cemented lens 4, respectively. The negative lens 24A is a biconcave lens, and the positive lens 24B is a positive meniscus lens having a convex surface facing the long conjugate side made of a glass material having a refractive index greater than 1.9. As a result, the cemented lens 24 has a positive refractive power as a whole, like the cemented lens 4.

With such a configuration, the refractive powers of all six lenses of the first lens group G21 of this modification are positive, negative, and negative in order from the long conjugate side, like the first lens group G1 of the above embodiment. , Negative, positive, negative.
Therefore, the first lens group G21 includes two positive lenses and four negative lenses, like the first lens group G1. The two positive lenses are arranged in a positional relationship such that the positive lens 4B, which is a positive lens made of a glass material having a refractive index greater than 1.9, is on the shorter conjugate side, that is, the side closer to the second lens group G22. ing.

  In the first lens group G21 of this modification example, it is preferable that the conditional expression (1) is satisfied, and it is more preferable that the conditional expression (1a) is satisfied, as in the first lens group G1 of the above embodiment.

The second lens group G21 is replaced with the cemented lens 26 and the lens 27, respectively, instead of the lenses 6 and 7, the diaphragm 8, the aspherical lens 9, the cemented lens 10, and the lenses 11 and 12 of the second lens group G2 of the above embodiment. A diaphragm 28, an aspherical lens 29, a cemented lens 30, and lenses 31 and 32.
The cemented lens 26 includes a negative lens 26A that is a biconcave lens and a positive lens 26B that is a biconvex lens, which are cemented in this order from the long conjugate side, and has a positive refractive power as a whole.
Similarly to the lens 7, the lens 27 is a positive meniscus lens having a convex surface facing the long conjugate side.
The aspheric lens 29 is a biconcave lens in which two concave surfaces are aspheric surfaces. Therefore, the aspherical lens 29 constitutes a negative lens unit composed of a single lens having two aspherical surfaces.
The cemented lens 30 includes a negative lens 30A and a positive lens 30B instead of the negative lens 10A and the positive lens 10B of the cemented lens 10, respectively, and has a negative refractive power as a whole.
However, the negative lens 30A is a negative meniscus lens having a concave surface facing the long conjugate side, and the positive lens 30B is a positive meniscus lens having a convex surface facing the long conjugate side.
Similarly to the lenses 11 and 12, the lenses 31 and 32 are each composed of a positive meniscus lens and a biconvex lens having a concave surface facing the long conjugate side.

With such a configuration, the refractive powers of all eight lenses of the second lens group G22 of the present modification are, in order from the long conjugate side, negative, positive, positive, negative, negative, positive, positive, and positive. Yes.
In this modification, an aspheric lens 29 which is a single lens having two aspheric surfaces and having negative refractive power is provided adjacent to the diaphragm 28 on the short conjugate side.

In the second lens group G22 of this modification, one negative lens 26A, two positive lenses 26B and a lens 27 are arranged on the long conjugate side with respect to the stop, and are positively refracted as a whole. A long conjugate side lens group which is a lens group having force is configured.
The aspherical lens 29, the cemented lens 30 composed of the negative lens 30A and the positive lens 30B, and the two lenses 31 and 32, which are positive lenses, are arranged at a short conjugate position with respect to the stop. A short conjugate side lens group which is a lens group having a positive refractive power is configured.

In the second lens group G22 of this modification example, it is preferable that the conditional expression (2) is satisfied, and it is more preferable that the conditional expression (2a) is satisfied, as in the second lens group G22 of the above embodiment.
Similarly, it is preferable that the conditional expression (3) is satisfied, and it is more preferable that the conditional expression (3a) is satisfied.
Similarly, it is preferable that the conditional expression (4) is satisfied, and it is more preferable that the conditional expression (4a) is satisfied.

As described above, the projection optical system 200 of the present modification has a configuration substantially the same as that of the first lens group G1 of the above embodiment in the first lens group G21. Further, in the second lens group G22, the negative lens 26A is added to the most conjugate side in the long conjugate side lens group, and two surfaces of the aspheric lens 29 which is a negative lens unit are aspherical. Accordingly, as in the above-described embodiment, positive spherical aberration can be corrected while suppressing the influence of aberration due to off-axis rays, so that it is possible to achieve good optical performance while having a small F number and a wide projection angle (field angle). Performance is obtained.
In addition, spherical aberration, field curvature, and distortion can be corrected more easily than in the above embodiment.
Further, since the added negative lens 26B constitutes the cemented lens 26 with the positive lens 26B and includes a total of three cemented lenses of the projection optical system 200, the chromatic aberration correction is further improved as compared with the above embodiment. It becomes easy.
In the first lens group G21, since the lens 25, which is a negative meniscus lens having a concave surface facing the long conjugate side, is arranged on the shortest conjugate side, it is easy to correct coma.
Moreover, when this modification takes the preferable form demonstrated above or a more desirable form, the effect similar to the above is acquired.

  In the above description, the first lens group G1, 21 has been described as an example in which the lenses 5 and 25, which are negative meniscus lenses with concave surfaces facing the long conjugate side, are provided on the shortest conjugate side, respectively. The shortest conjugate side lens of the first lens group may not be a meniscus lens as long as it is a negative lens.

  In addition, all the components described in the above embodiments and modifications can be implemented by appropriately changing or deleting combinations within the scope of the technical idea of the present invention. For example, the preferred embodiments and the more desirable embodiments of the above-described embodiments and modifications can be implemented in appropriate combination.

Here, a case will be described where the names of the correspondence relationships between the terms of the above embodiments and the terms of the claims are different.
Each of the aspheric lenses 9 and 29 is an embodiment of a negative lens unit.

Next, Example 1, which is a first numerical example of the projection optical system 100 according to the embodiment described above, will be described with reference to FIGS. 1, 3A, 3B, and 3C. .
FIGS. 3A, 3B, and 3C are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion of a numerical example of the projection optical system according to the embodiment of the present invention.

The table below shows the configuration parameters of the projection optical system 100 of the first embodiment. It should be noted that the surface number i (i represents a natural number) increases from the longest conjugate side lens surface of the lenses constituting the projection optical system 100 to the first conjugate side. So that they are numbered.
Further, the curvature radius R _i is the curvature radius of the lens surface corresponding to each surface number i, and the surface interval D _i is the axial upper surface interval between the lens surface with surface number i and the lens surface with surface number i + 1, and the unit is (Mm). Correspondences between the respective curvature radii R _i and the surface distances D _i and the respective lenses are denoted by reference symbols R _i and D _i in FIG.
Refractive indexes N and ν _d indicate the refractive index and Abbe number of each lens, respectively. The refractive index is shown for d-line (wavelength 587.56 nm).

  The aspherical shape is given by the following equation (5) as the sag amount (displacement amount in the optical axis direction) z of the surface parallel to the optical axis when the vertex of the surface is the origin and h is the height from the optical axis. (Example 2 is the same).

  Here, c is the curvature at the top, that is, c = 1 / r, where r is the paraxial radius of curvature. K is a conic coefficient, A, B, C, D, E, F, G, H, and J are 4th, 6th, 8th, 10th, 12th, 14th, 16th, 18th, respectively. , 20th-order deformation coefficient. The deformation coefficients not listed in the table below are zero.

Surface number Curvature radius (R) Surface spacing (D) Refractive index (N) Abbe number (ν _d )
1 R ₁ = 59.09 D ₁ = 4.54 N ₁ = 1.713 ν ₁ = 53.9
2 R ₂ = -3490.92 D ₂ = 0.20
3 R ₃ = 52.16 D ₃ = 1.50 N ₂ = 1.487 ν ₂ = 70.4
4 R ₄ = 17.87 D ₄ = 5.54
5 R ₅ = 316.76 D ₅ = 1.20 N ₃ = 1.487 ν ₃ = 70.4
6 R ₆ = 19.72 D ₆ = 4.92
7 R ₇ = -54.74 D ₇ = 1.00 N ₄ = 1.487 ν ₄ = 70.4
8 R ₈ = 20.65 D ₈ = 4.40 N ₅ = 1.904 ν ₅ = 31.3
9 R ₉ = 1678.02 D ₉ = 2.94
10 R ₁₀ = -21.84 D ₁₀ = 1.65 N ₆ = 1.847 ν ₆ = 23.8
11 R ₁₁ = -81.39 D ₁₁ = 1.83
12 R ₁₂ = 1120.14 D ₁₂ = 3.72 N ₇ = 1.713 ν ₇ = 53.9
13 R ₁₃ = -31.47 D ₁₃ = 0.20
14 R ₁₄ = 21.39 D ₁₄ = 4.50 N ₈ = 1.697 ν ₈ = 55.5
15 R ₁₅ = 303.60 D ₁₅ = 8.48
16 R ₁₆ = ∞ (aperture) D ₁₆ = 1.47
17 R ₁₇ = -52.15 D ₁₇ = 1.22 N ₉ = 1.821 ν ₉ = 24.1
18 Aspherical surface [1] D ₁₈ = 2.79
19 R ₁₉ = -16.41 D ₁₉ = 1.00 N ₁₀ = 1.805 ν ₁₀ = 25.5
20 R ₂₀ = 263.59 D ₂₀ = 4.40 N ₁₁ = 1.713 ν ₁₁ = 53.9
21 R ₂₁ = -20.64 D ₂₁ = 0.20
22 R ₂₂ = -152.71 D ₂₂ = 3.44 N ₁₂ = 1.713 ν ₁₂ = 53.9
23 R ₂₃ = -31.38 D ₂₃ = 0.20
24 R ₂₄ = 51.34 D ₂₄ = 4.55 N ₁₃ = 1.834 ν ₁₃ = 37.3
25 R ₂₅ = -62.17 D ₂₅ = 1.00
26 R ₂₆ = ∞ D ₂₆ = 21.60 N ₁₄ = 1.516 ν ₁₄ = 64.2
27 R ₂₇ = ∞ D ₂₇ = 2.10
28 R ₂₈ = ∞ D ₂₈ = 2.30 N ₁₅ = 1.458 ν ₁₅ = 67.8
29 R ₂₉ = ∞ D ₂₉ = 2.10
30 ∞ (Display element surface) D ₃₀ = 0.00
Aspherical surface [1]:
c 1 / 166.14 (r = 166.14)
k 0
A 0.5100x10 ^-4 B 0.1217x10 ^-6 C -0.7743x10 ^-9
D 0.4752x10 ^-11

With such a configuration, as shown in Table 1, the focal length f of the entire projection optical system 100 of the present embodiment is 19.0 mm, and the focal length f ₁ of the first lens group G1 is −20.7 mm. the focal length _{f 2} of the second lens group G2 is 28.0 mm, the focal length _{f 2a} of the long conjugate side lens group 18.6 mm, the focal length _{f 2b} of the short conjugate side lens group 27.3 mm, of the negative lens unit The focal length f _nl2 is −48.2 mm. The F number Fno is 1.5 and the half angle of view is 26 °.
Therefore, the values corresponding to the conditional expressions (1) to (4) are | f ₁ | /f=1.09, f ₂ /f=1.47, f _2a / f _2b = 0.68, | F _nl2 | /f=2.54.

Also, spherical aberration, astigmatism, and distortion due to the projection optical system 100 of the present embodiment are shown in FIGS. 3A, 3B, and 3C, respectively.
In the spherical aberration diagrams and distortion diagrams (FIGS. 3A and 3C), the wavelength is 638 nm (shown by a solid line), the wavelength is 520 nm (shown by a one-dot chain line), and the wavelength is 455 nm (shown by a two-dot chain line). .) Shows spherical aberration and distortion at each wavelength. However, the distortion aberration of the present embodiment is not distinguishable because the three curves are almost overlapped.
The astigmatism diagram (FIG. 3 (b)) similarly shows astigmatism for sagittal rays at wavelengths of 638 nm, 520 nm, and 455 nm as curves S1, S2, and S3, respectively, and similarly for astigmatism rays for tangential rays. Point aberrations are indicated by curves T1, T2, and T3, respectively.

Thus, as shown in Table 1, the projection optical system 100 of the present example satisfies all the conditional expressions (1) to (4). Furthermore, the above conditional expressions (1a) to (4a) are all satisfied.
In addition, as shown in FIGS. 3A, 3B, and 3C, it can be seen that the projection optical system 100 of the present embodiment is well corrected for spherical aberration, astigmatism, and distortion. .
In addition, the half field angle ω is 26 ° and a wide field angle, and the F number is 1.5 and the optical system is bright.

Next, with reference to FIGS. 2, 4A, 4B, and 2C for Example 2, which is a second numerical example of the projection optical system 200 according to the modification of the embodiment described above. I will explain.
4A, 4B, and 4C are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion of a numerical example of the projection optical system according to the modification of the embodiment of the present invention. .

The table below shows the configuration parameters of the projection optical system 100 of the first embodiment. The way of viewing the table below is the same as in the first embodiment, and the correspondence between each radius of curvature R _i , surface interval D _i and each lens is indicated by reference signs R _i and D _i in FIG.

Surface number Curvature radius (R) Surface spacing (D) Refractive index (N) Abbe number (ν _d )
1 R ₁ = 58.50 D ₁ = 4.30 N ₁ = 1.786 ν ₁ = 43.9
2 R ₂ = 329.16 D ₂ = 0.20
3 R ₃ = 47.28 D ₃ = 1.00 N ₂ = 1.487 ν ₂ = 70.4
4 R ₄ = 15.60 D ₄ = 6.63
5 R ₅ = 96.37 D ₅ = 1.00 N ₃ = 1.487 ν ₃ = 70.4
6 R ₆ = 21.37 D ₆ = 4.48
7 R ₇ = -80.53 D ₇ = 1.00 N ₄ = 1.487 ν ₄ = 70.4
8 R ₈ = 18.71 D ₈ = 4.28 N ₅ = 1.904 ν ₅ = 31.3
9 R ₉ = 85.54 D ₉ = 3.69
10 R ₁₀ = -21.70 D ₁₀ = 1.00 N ₆ = 1.762 ν ₆ = 26.6
11 R ₁₁ = -67.89 D ₁₁ = 2.00
12 R ₁₂ = -243.54 D ₁₂ = 1.00 N ₇ = 1.847 ν ₇ = 23.8
13 R ₁₃ = 38.56 D ₁₃ = 5.30 N ₈ = 1.786 ν ₈ = 43.9
14 R ₁₄ = -33.65 D ₁₄ = 0.20
15 R ₁₅ = 23.62 D ₁₅ = 4.38 N ₉ = 1.786 ν ₉ = 43.9
16 R ₁₆ = 982.39 D ₁₆ = 7.70
17 R ₁₇ = ∞ (aperture) D ₁₇ = 3.97
18 Aspherical surface [1] D ₁₈ = 1.45 N ₁₀ = 1.821 ν ₁₀ = 24.1
19 Aspherical surface [2] D ₁₉ = 2.84
20 R ₂₀ = -19.03 D ₂₀ = 1.00 N ₁₁ = 1.847 ν ₁₁ = 23.8
21 R ₂₁ = -112.36 D ₂₁ = 3.50 N ₁₂ = 1.487 ν ₁₂ = 70.4
22 R ₂₂ = -25.58 D ₂₂ = 0.20
23 R ₂₃ = -326.23 D ₂₃ = 5.18 N ₁₃ = 1.697 ν ₁₃ = 55.5
24 R ₂₄ = -23.65 D ₂₄ = 0.20
25 R ₂₅ = 58.68 D ₂₅ = 4.41 N ₁₄ = 1.834 ν ₁₄ = 37.3
26 R ₂₆ = -84.66 D ₂₆ = 1.00
27 R ₂₇ = ∞ D ₂₇ = 21.60 N ₁₅ = 1.517 ν ₁₅ = 64.2
28 R ₂₈ = ∞ D ₂₈ = 2.10
29 R ₂₉ = ∞ D ₂₉ = 2.30 N ₁₆ = 1.458 ν ₁₆ = 67.8
30 R ₃₀ = ∞ D ₃₀ = 2.10
31 ∞ (Display element surface) D ₃₁ = 0.00
Aspherical surface [1]:
c -1 / 51.84 (r = -51.84)
k 0
A 0.4039x10 ^-4 B -0.5209x10 ^-6 C 0.7317x10 ^-9
D 0.7128x10 ^-11
Aspherical surface [2]:
c -1 / 5616.69 (r = -5616.69)
k 0
A 0.8940x10 ^-4 B -0.3758x10 ^-6 C 0.5783x10 ^-9
D 0.5901x10 ^-11

With such a configuration, as shown in Table 1, the focal length f of the entire projection optical system 200 of the present embodiment is 19.0 mm, and the focal length f ₁ of the first lens group G21 is −22.2 mm. the focal length _{f 2} of the second lens group G22 is 30.0 mm, the focal length _{f 2a} of the long conjugate side lens group 19.4 mm, the focal length _{f 2b} of the short conjugate side lens group 29.8 mm, of the negative lens unit The focal length f _nl2 is −63.7 mm. The F number Fno is 1.6 and the half angle of view is 28 °.
Therefore, the values corresponding to the conditional expressions (1) to (4) are | f ₁ | /f=1.17, f ₂ /f=1.58, f _2a / f _2b = 0.65, | F _nl2 | /f=3.35.

Also, spherical aberration, astigmatism, and distortion due to the projection optical system 200 of this embodiment are shown in FIGS. 4A, 4B, and 4C, respectively.
Note that each aberration diagram is viewed in the same manner as in FIGS. 3A, 3B, and 3C.

Thus, as shown in Table 1, the projection optical system 200 of this embodiment satisfies all the conditional expressions (1) to (4). Furthermore, the above conditional expressions (1a) to (4a) are all satisfied.
Further, as shown in FIGS. 4A, 4B, and 4C, it can be seen that the projection optical system 200 of the present example is well corrected for spherical aberration, astigmatism, and distortion. .
In addition, the half field angle ω is 28 ° and the wide field angle, but the F number is 1.6 and the optical system is bright.

4B, 24B positive lenses (positive lenses made of glass with a refractive index greater than 1.9)
5,25 lens (negative meniscus lens with concave surface facing long conjugate side)
8, 28 Aperture 9, 29 Aspherical lens (negative lens unit)
10, 30 Joint lens 10A, 30A Negative lens 10B, 30B Positive lens 100, 200 Projection optical system G1, G21 First lens group G2, G22 Second lens group I Element display surface

Claims (5)

A projection optical system comprising a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the long conjugate side as a lens group ,
The first lens group includes:
In order from the long conjugate side, a positive lens, at least three negative lenses, a positive lens made of a glass material having a refractive index greater than 1.9, and a negative meniscus lens having a concave surface facing the long conjugate side are arranged.
The second lens group includes:
In order from the long conjugate side, a long conjugate side lens group having a positive refractive power, a stop , and a short conjugate side lens group having a positive refractive power are arranged and configured.
The short conjugate side lens group is:
At least a negative lens unit having a negative refractive power and having aspheric one surface, the projection optical system, characterized in that it is disposed adjacent to the short conjugate side to the diaphragm. When the focal length of the entire system is f, the focal length of the first lens group is f ₁ , and the focal length of the second lens group is f ₂ , the following conditional expressions (1) and (2) are satisfied. The projection optical system according to claim 1.
0.85 <| f ₁ | / f <1.3 (1)
1.2 <f ₂ /f<1.9 (2) The second lens group includes :
The following conditional expression (3) is satisfied, where f _{2a is} a focal length of the long conjugate side lens group and f _2b is a focal length of the short conjugate side lens group. The projection optical system described.
0.52 <f _2a / f _2b <0.82 (3) The negative lens focal length of the unit is taken as f _nl2, projection optical system according to any one of claims 1 to 3, characterized by satisfying the following conditional expression (4).
2.0 <| f _nl2 | / f <4.0 (4)
Here, f is the focal length of the entire system. The long conjugate side lens group includes at least two positive lenses,
The short conjugate side lens group includes, in order from the long conjugate side, the negative lens unit, a cemented lens composed of a negative lens and a positive lens, and at least two positive lenses . The projection optical system according to any one of the above.

Images