JP2021036258A - Projection optical system and image projection device - Google Patents

Abstract

To provide a projection optical system which has an ultra wide view angle and yet offers good optical performance over a wide projection distance range.SOLUTION: A projection optical system provided herein comprises a reduction-side optical system 102 having positive refractive power and a magnification-side optical system comprising a reflective optical element and having positive refractive power, arranged in order from the reduction conjugate side, and is configured to re-image an intermediate image formed by the reduction-side optical system 102 using the magnification-side optical system. The magnification-side optical system is stationary while focusing. The reduction-side optical system 102 comprises multiple lens groups configured to move along an optical axis, of which at least three lens groups have positive, negative, and negative refractive power in order from the magnification conjugate side, and are configured to move in the same direction.SELECTED DRAWING: Figure 2

Description

The present invention relates to a projection optical system, and is particularly suitable for an image projection device such as a projector that magnifies and projects an image displayed on an image display device.

An image projection device (projector, etc.) is a light modulation element in which a light modulation element such as a liquid crystal and a light beam emitted from a light source means such as a lamp or a semiconductor laser are set to a desired state (condensation degree, spectrum, uniformity, etc.). It is composed of an illumination optical system that guides and illuminates the light, and a projection optical system that magnifies and projects the light modulated by the light modulation element onto a projected surface such as a screen.

Depending on the type and configuration of the light modulation element, a prism for color synthesis, a PBS (polarization beam splitter) for polarization separation, a TIR prism, or the like is inserted between the light modulation element and the projection optical system.

Therefore, the projection optical system is required to secure the back focus and have good telecentricity.

Usually, the retrofocus type is often used to satisfy these two conditions.

In addition, higher definition of image display elements is required, and higher performance corresponding to resolutions exceeding full HD is required, and wide-angle lens capable of projecting a large image at a short distance is strongly desired.

However, if the retrofocus type is used to widen the angle, there is a problem that the lens on the projection surface side becomes extremely large.

On the other hand, a projection optical system having an intermediate image formation has been proposed in which a display image of an image display element is once imaged by a refractive optical system and the image is magnified and projected onto a projected surface by a reflection optical system (patented). Documents 1 and 2).

However, in such an ultra-wide-angle projection optical system, changes in curvature of field and distortion due to changes in the projection distance are large, which poses a problem during focusing.

Another problem is the change in chromatic aberration of magnification due to focusing.

In Patent Document 1, a first focus group having a negative refractive power among two or three lens groups performing focus singing and a group having a positive refractive power among the other focus groups are the first focus group. The group with negative refractive power in the same direction as the above discloses a focus method that suppresses the change in distortion by moving in the opposite direction, but there is no disclosure about curvature of field and chromatic aberration of magnification, and aberration correction is performed. It may not be enough.

Further, in Patent Document 2, from the magnifying conjugate side, the first lens group having a positive or negative refractive power, the second lens group having a negative refractive power, and the third lens having a positive refractive power are moved in a predetermined direction. Although we disclose a focus method that suppresses curvature of field, distortion, and changes in chromatic aberration by moving each, the focus range is 100 inches, especially at a distance, compared to 80 inches for the projected screen size at a reference distance. Therefore, there is a possibility that the aberration correction is not sufficient when projecting on a larger screen, which is frequently used by the image projection device.

In addition, the telecentricity is not sufficient, and it cannot be said that the desired characteristics of the projection optical system are sufficiently satisfied.

Japanese Unexamined Patent Publication No. 2014-225041 Japanese Unexamined Patent Publication No. 2017-44914

Therefore, an object of the present invention is to provide a projection optical system having an ultra-wide angle and good optical performance over a wide projection distance range.

In order to achieve the above object, the projection optical system according to the present invention is
It has a reduction side optical system having a positive refractive force in order from the reduction conjugate side, and a magnifying side optical system having a positive refractive power including a reflective optical element, and an intermediate image by the reduction side optical system is displayed on the enlargement side optical system. An optical system to be reimaged, the magnifying side optical system is fixed at the time of focusing, and the reducing side optical system has a plurality of lens groups moving along an optical axis, of which at least three lens groups are , It has a positive refractive force, a negative refractive force, and a negative refractive force in order from the expansion conjugate side, and is characterized by moving in the same direction.

According to the present invention, it is possible to provide a projection optical system having good optical performance over a wide projection distance range while having an ultra-wide angle. In addition, it is possible to secure back focus and achieve good telecentricity at the same time.

Optical path diagram at the wide-angle end of the projection optical system according to the first embodiment Sectional drawing of the reduction side optical system which concerns on 1st Embodiment Aberration diagram of the projection optical system according to the first embodiment Magnification chromatic aberration of the projection optical system according to the first embodiment Optical path diagram at the wide-angle end of the projection optical system according to the second embodiment Optical path diagram at the wide-angle end of the projection optical system according to the third embodiment Sectional drawing of the reduction side optical system which concerns on 3rd Embodiment Aberration diagram of the projection optical system according to the third embodiment Magnification chromatic aberration of the projection optical system according to the third embodiment Optical path diagram at the wide-angle end of the projection optical system according to the fourth embodiment Cross-sectional view of the reduction side optical system according to the fourth embodiment Aberration diagram of the projection optical system according to the fourth embodiment Magnification chromatic aberration of the projection optical system according to the fourth embodiment

Hereinafter, the projection optical system according to the embodiment of the present invention will be described with reference to the drawings.

The drawings shown below may be drawn at a scale different from the actual one in order to make the present invention easy to understand.

[First Embodiment]
FIG. 1 shows an optical path diagram of the projection optical system 100 according to the first embodiment.

Since this projection optical system is a zoom lens having a scaling function, FIG. 1 shows an optical path diagram at a wide-angle end at a projection distance of 775 mm.

The projection optical system 100 is composed of an expansion side optical system 101 and a reduction side optical system 102.

The magnifying side optical system 101 is composed of a convex reflector M11 having a negative power and a positive concave reflector M12 in order from the magnifying conjugate side, and has a positive power as the magnifying side optical system 101.

The reduction side optical system 102 is composed of lens groups B1, B2, B3, B4, B5, and B6 whose powers are negative, positive, positive, negative, positive, and positive, respectively, in order from the expansion conjugate side. ST is an aperture stop.

A color synthesis optical system 200 made of a synthetic prism, PBS, or the like is inserted between the reduction side optical system 102 and the light modulation element 300 which is a reduction side conjugate surface. The color synthesis optical system 200 guides the light modulated by the light modulation element 300 to the projection optical system 100. As the light modulation element, a liquid crystal panel, a micromirror device, or the like is used.

The reduction side optical system 102 forms an intermediate image 301 which is a conjugate image of the light modulation element 300, and the enlargement side optical system 101 reimages the intermediate image 301 on the enlargement side conjugate surface (not shown).

The conjugate image 301 by the reduction side optical system 102 has a large curvature of field, and the conjugate points of each angle of view are curved in the optical axis direction.

The magnifying side optical system 101 generates curvature of field in the opposite direction so as to correct the curvature of field of the intermediate image 301, and the curvature of field is satisfactorily corrected on the magnifying side conjugate surface.

In the projection optical system of the present embodiment, the magnifying side optical system 101 including the convex reflector M11 and the concave reflector M12 mainly has a wide-angle function, and the reduction side optical system 102 ensures back focus and good telecentricity. It is configured to carry.

Further, the residual aberration of the reduction side optical system 102 is corrected by the expansion side optical system 102. With such a configuration, good optical performance is realized while having an ultra-wide angle.

For each lens group constituting the reduction side optical system 102, the lens group B1 has a positive power of moving in the optical axis direction of the reduction side optical system 102 during focusing due to a change in projection distance. It is composed of a negative lens group B1b, a negative power lens group B1c, and a fixed power positive lens group B1d during focusing.

The lens groups B1a, B1b, and B1c are composed of single lenses L11, L12, and L13, respectively, and the lens group B1d is composed of two single lenses L14 and L15.

The powers of the single lenses L11, L12, L13, L14, and L14 are positive, negative, negative, positive, and positive, respectively.

The lens group B2 is composed of only a single lens L16 having a positive power.

The lens group B3 is composed of a bonded lens in which a single lens L17 having a negative power and a single lens L18 having a positive power are bonded together.

The lens group B4 is composed of only a single lens L19 having a negative power.

The lens group B5 is composed of single lenses L20 and L23 having positive and positive powers, respectively, and a bonded lens in which L21 having negative power and L22 having positive power are bonded together.

The lens group B6 is composed of only a single lens L24 having a positive power.

In the present embodiment, the scaling is performed by moving the four lens groups B2, B3, B4, and B5 constituting the reduction side optical system 102 in different trajectories in the optical axis direction of the reduction side optical system 102. It is said. The aperture stop ST moves together with the lens group B4.

Tables 1-1 to 1-3 show various numerical values of the projection optical system according to this embodiment.

(A) shows the lens configuration, from the magnifying conjugate side to the paraxial radius of curvature r (mm) of each surface, the distance d (mm) between each surface and the next surface, and the refractive index n with respect to the d line of each optical member. The Abbe number ν is described. ST indicates the position of the aperture stop. Regarding the reflector, the refractive index n and the Abbe number ν need not be considered as optical actions, and are therefore omitted.

The surface marked with * on the left side has an aspherical shape represented by the equation (1).

y is the radial distance from the optical axis, z is the sag amount of the surface in the optical axis direction, r is the radius of curvature of the near axis, and k is the cornic coefficient. The sign of z is positive in the direction from the expansion conjugate side to the reduction conjugate side.

(B) shows the coefficients of each surface. In Tables 1-1 to 1-3, "E ± x" means "10 ^{± x} ". In addition, all the coefficients not particularly described are 0.

In the present embodiment, not only each single lens but also the convex reflector M11 and the concave reflector M12 have a rotationally symmetric surface shape around the optical axis, and a part thereof is cut out.

By doing so, it is possible to focus and change the magnification simply by changing the distance between each lens group composed of rotationally symmetric lenses.

When both or one of the convex reflector M11 and the concave reflector M12 has a free-form surface shape that is not rotationally symmetric, the imaging magnification is generally different in each cross section including the optical axis and whose rotation angle is changed around the optical axis.

Therefore, it becomes necessary to perform focusing and scaling by combining the movement of a free-form surface-shaped element that is not rotationally symmetric and the movement in the vertical direction of the optical axis as well as the movement in the optical axis direction, which makes it difficult to ensure accuracy.

Further, the convex reflector M11 and the concave reflector M12 whose outer diameter shape is not completely rotationally symmetric are not suitable for movement because the holding method is complicated. Therefore, in the present embodiment, the focusing and scaling are performed by the reduction side optical system 102 composed of only the lenses having a rotationally symmetric shape including the outer shape.

In (C), the values corresponding to each projection distance are shown for each surface spacing (group spacing) that changes during focusing, and the values at the wide-angle end and the telephoto end are shown for each plane spacing (group spacing) that changes during scaling. ,
FIG. 2 shows a cross-sectional view of the reduction side optical system 102 of the projection optical system according to the present embodiment at a wide angle end (projection distance 4650 mm) and close distance (projection distance 543 mm).

In the present embodiment, focusing is performed by moving the lens groups B1a, B1b, and B1c in the same direction. The amount of movement is different.

As indicated by the arrows in FIG. 2, in the present embodiment, the lens groups B1a, B1b, and B1c all move to the magnifying conjugate side during focusing from a distance to a close distance.

In an ultra-wide-angle projection optical system with a half-angle of view of about 70 ° as in the present embodiment, the change in chromatic aberration of magnification is satisfactorily suppressed while correcting the curvature of field and distortion that occur when the projection distance changes during focusing. There is a need to.

Therefore, in the present embodiment, the floating focus method is adopted in which the lens groups B1a, B1b, and B1c move with different movement amounts, and the relationship between the power arrangement and movement of each group is optimally set.

Specifically, first, the lens groups B1a and B1b mainly correct the changes in curvature of field and distortion, and the lens group B1c mainly corrects the focus (focus), so that the aberration can be highly corrected. It has a good structure. ..

The lens groups B1a and B1b are lens groups having a high light passing height among the lens groups B1a, B1b and B1c, and are suitable for correcting off-axis aberrations such as curvature of field and distortion.

In addition, the lens groups B1a and B1b move with different movement amounts so that curvature of field and distortion can be highly corrected.

By the way, as described above, the lenses groups B1a and B1b have positive and negative powers, respectively, and move in the same direction during focusing.

In this way, by configuring the lens groups B1a and B1b having different sign powers to move in the same direction, it is possible to correct curvature of field and distortion while suppressing changes in chromatic aberration of magnification during focusing. It has become.

Furthermore, changes in the angle and height of the incident light beam on the lens group B1c due to the movement of the lens groups B1a and B1b can be suppressed, which is also effective in suppressing fluctuations in off-axis aberration due to the lens group B1c.

When the focal length of the lens group B1a is fa and the focal length of the lens group B1b is fb,

It is desirable to satisfy.

When it is below the lower limit of the equation (2), the absolute value of the power of the lens group B1b becomes too large than the absolute value of the power of the lens group B1a, and when focusing is performed so as to correct curvature of field and distortion. The fluctuation of the chromatic aberration of magnification becomes large.

When the upper limit of the equation (2) is exceeded, on the contrary, the absolute value of the power of the lens group B1a becomes too large than the absolute value of the power of the lens group B1b, and the curvature of field and the distortion are corrected in the same manner. Fluctuations in chromatic aberration of magnification during focusing become large.

More preferably

It is good to be satisfied.

In the present embodiment, fa / fb is −1.047, which is configured to satisfy the formula (3).

The lens group B1c is a lens group having the lowest light ray passing height among the lens groups B1a, B1b, and B1c, and can suppress fluctuations in off-axis aberration due to movement during focusing. I mainly try to focus.

Further, the absolute value of the power of the lens group B1c is set to be the largest among the lens groups B1a, B1b, and B1c.

By doing so, the amount of movement of the lens group B1c can be reduced, and the fluctuation of the light passing height due to the movement of the lens group B1c can be suppressed to be small. This configuration is more desirable in order to suppress fluctuations in off-axis aberrations.

Further, it is more desirable that the lens group B1c includes a lens having an aspherical shape on at least one surface.

Having an aspherical optical surface makes it possible to further reduce fluctuations in off-axis aberrations.

In the present embodiment, the lens group B1c is composed of one single lens L13, but the L13 has an aspherical shape on both sides to further reduce fluctuations in off-axis aberrations.

As described above, the lens group B1c has a negative power and is configured to move in the same direction as the lens groups B1a and B1b during focusing.

With the above configuration, the distance between the lens groups B1b and B1c can be narrowed, which is advantageous for miniaturization.

For example, when the power of the lens group B1c is positive and the lens group B1c is configured to move in the opposite direction to the lens groups B1a and B1b during focusing, in addition to the interval dm when the lens groups B1b and B1c are closest to each other. Therefore, a space of dmin + Db + Dc including the movement amount Db of the lens group B1b and the movement amount Dc of the lens group B1c is required.

On the other hand, when the lens groups B1a and B1b and the lens group B1c are configured to move in the same direction during focusing as in the present embodiment, a space of dmin + Db may be sufficient.

By the way, when the combined focal length fab of the lens groups B1a and B1b and the focal length of the lens group B1c are fc when the absolute value of the combined focal lengths of the lens groups B1a and B1b in the focusingable range is maximized,

It is desirable to satisfy.

If it is below the lower limit of the equation (4), the absolute value of the power of the lens groups B1a and B1b becomes too small, and the curvature of field and distortion due to the lens groups B1a and B1b are insufficiently corrected.

When the upper limit of the equation (4) is exceeded, on the contrary, the absolute value of the power of the lens group B1c becomes too small, the amount of movement of the lens group B1c increases, and the fluctuation of the off-axis aberration due to B1c becomes large.

More preferably

It is good to be satisfied.

In the present embodiment, | fc / fab | is 0.021, which is configured to satisfy the equation (5).

FIG. 3 shows longitudinal aberration diagrams at projection distances of 543 mm, 775 mm, and 4650 mm in the present embodiment. In these figures, spherical aberration, curvature of field / astigmatism, and distortion with respect to the d-line are shown.

Each projection distance is a close, reference, and distant projection distance, and when the aspect ratio of the projected image is 16:10, the size of the projected image is 70 inches, 100 inches, and 600 inches.

The aberration diagram of FIG. 3 is an aberration diagram when the enlarged conjugated side is the object side and the reduced conjugated side is the image side so that the scale is easy to understand.

In this embodiment, the image height 0 is not used, but the spherical aberration is calculated for the image height 0 (axial luminous flux) by definition.

Regarding curvature-of-field curvature / astigmatism and distortion, the image height 0 is usually used as a reference, but since the image height 0 is not used in this embodiment, the image height is calculated based on the minimum image height in the actually usable range. Has been done. Therefore, the value of the image height 0 is not 0. Further, even if the value at the image height 0 deviates greatly from 0, it does not matter.

When used as a projection optical system, the object side and the image side are reversed, but spherical aberration and curvature of field / astigmatism may be converted using the longitudinal magnification. Since distortion is originally calculated as a ratio, it should be noted that the absolute value does not change but the sign is inverted.

It can be seen that all the aberrations are satisfactorily corrected at each projection distance.

FIG. 4 shows chromatic aberration of magnification at projection distances of 543 mm, 775 mm, and 4650 mm in the present embodiment.

It can be seen that the chromatic aberration of magnification is satisfactorily corrected at any projection distance, and the change in chromatic aberration of magnification due to focusing is well suppressed.

As described above, the projection optical system 100 according to the present embodiment has an expansion side optical system 101 including a reflection optical system and a reduction side optical system, which are refraction optical systems, arranged on the expansion conjugate side with the intermediate image 301 interposed therebetween. It is composed of the system 102 and has a focusing and scaling function.

The scaling is realized by moving four lens groups B2, B3, B4, and B5 along the optical axis among the plurality of lens groups constituting the reduction side optical system 102.

Focusing is realized by moving the lens groups B1a, B1b, and B1c arranged from the magnifying conjugate side along the optical axis among the plurality of lens groups constituting the reduction side optical system 102.

At this time, the lenses B1a and B1b having high light passing heights have positive and negative powers, respectively, and have opposite signs. By moving in the same direction during focusing, the projection distance is suppressed while suppressing the change in chromatic aberration of magnification. It satisfactorily corrects curvature of field and distortion due to changes.

The lens group B1c having a low light ray passing height has a negative power and moves in the same direction as the lens groups B1a and B1b during focusing, so that the lens group B1c has an advantageous configuration for miniaturization and changes in off-axis aberration. Focus while suppressing.

With such a configuration, curvature of field and distortion due to changes in the projection distance that occur in the ultra-wide-angle projection optical system are satisfactorily corrected, and fluctuations in chromatic aberration of magnification are suppressed, resulting in an ultra-wide-angle yet wide range. We have achieved a projection optical system with good optical performance in the projection range.

The present invention is not limited to the present embodiment, and changes can be made within the scope of the gist thereof. For example, the reduction side optical system 102 has a magnification-changing function by moving four lens groups, but the present invention is not limited to this, and the number of groups can be changed. Moreover, it is not necessary to have the scaling function itself.

[Second Embodiment]
FIG. 5 shows an optical path diagram of the projection optical system 100 according to the second embodiment.

The projection optical system 100 is the first except that the optical path is folded back by the plane reflectors FM1 and FM2 between the convex reflector M11 and the concave reflector M12 and between the magnifying side optical system 101 and the reducing side optical system 102. It is the same as the embodiment.

In the present embodiment, in order to reduce the installation space when combined with the image projection device, the optical path of the projection optical system 100 is folded back by the plane reflectors FM1 and FM2, and the projection direction of the image is changed from the first embodiment. ..

When the optical path is bent and the projection direction is reversed as in the present embodiment, the image is projected onto the projection optical system 100 on the side where the image projection device is arranged. The installation space can be reduced by the size of the image projection device.

In the present embodiment, the plane mirrors FM1 and FM2 are arranged at an angle of 45 ° so as to bend the optical path by 90 °, respectively.

By doing so, even when the optical path is bent, the convex mirror M12 and the concave mirror M22 can maintain a rotationally symmetric surface shape around the optical axis after bending without forming a free curved surface shape.

Tables 2-1 to 2-3 show various numerical values of the projection optical system according to this embodiment. Tables 2-1 to 2-3 have the same definition of each element as Tables 1-1 to 1-3, but care must be taken regarding the coordinate system due to the bending of the optical path.

As for the surface spacing, the spacing along the optical axis direction in each of the bent sections is described.

The definition of the aspherical shape is given by the equation (1) as in the first embodiment.

However, in the second embodiment, since the expansion conjugate side and the reduction conjugate side exist in the same direction, the sign of the sag amount z of the surface is the direction toward the reduction conjugate side along the direction of the optical axis bent from the expansion conjugate side. Is positive.

In the present embodiment and the first embodiment, the surface shapes and the like of the corresponding elements are the same, the optical action is also the same, and various aberrations are the same.

Therefore, in the present embodiment as well, as in the first embodiment, a projection optical system having an ultra-wide angle and good optical performance in a wide projection distance range is achieved.

The present invention is not limited to the present embodiment, and changes can be made within the scope of the gist thereof. For example, the method of bending the optical path is not limited to the method using two planar reflectors, and for example, the optical path may be bent and the projection direction may be changed by using only one planar reflector. On the contrary, even if the number of plane reflectors is increased and bent, the optical performance is not affected, so it does not matter.

[Third Embodiment]
FIG. 6 shows an optical path diagram of the projection optical system 100 according to the third embodiment.

Since this projection optical system is a zoom lens having a scaling function, FIG. 6 shows an optical path diagram at a wide-angle end at a projection distance of 775 mm.

The projection optical system 100 is composed of an expansion side optical system 101 and a reduction side optical system 102 as in other embodiments.

The magnifying side optical system 101 is composed of a convex reflector M21 having a negative power and a positive concave reflector M22 in order from the magnifying conjugate side, and has a positive power as the magnifying side optical system 101.

Unlike the first and second embodiments, the reduction side optical system 102 has lens groups B1, B2, and B3 whose powers are negative, positive, positive, positive, positive, negative, positive, and positive, respectively, in order from the expansion conjugate side. , B4, B5, B6, B7, B8.

Further, as in the second embodiment, the optical path is folded back by the plane reflectors FM1 and FM2 between the convex reflector M21 and the concave reflector M22, and between the magnifying side optical system 101 and the reducing side optical system 102.

For each lens group constituting the reduction side optical system 102, the lens group B1 has a positive power of moving in the optical axis direction of the reduction side optical system 102 during focusing due to a change in projection distance. It is composed of a negative lens group B1b and a negative power lens group B1c.

The lens groups B1a, B1b, and B1c are composed of single lenses L31, L32, and L33, respectively, and the powers of the single lenses L31, L32, and L33 are positive, negative, and negative, respectively.

The lens group B2 is composed of only a single lens L34 having a positive power.

The lens group B3 is composed of only a single lens L35 having a positive power.

The lens group B4 is composed of only a single lens L36 having a positive power.

The lens group B5 is composed of a bonded lens in which a single lens L37 having a negative power and a single lens L38 having a positive power are bonded together.

The lens group B6 is composed of only a single lens L39 having a negative power.

The lens group B7 is composed of single lenses L40 and L43 having positive and positive powers, respectively, and a bonded lens in which L41 having negative power and L42 having positive power are bonded together.

The lens group B8 is composed of only a single lens L44 having a positive power.

In the present embodiment, the scaling is performed by changing the spacing of each lens group constituting the reduction side optical system 102 as in the other embodiments.

In the present embodiment, the magnification is changed by moving the six lens groups B2, B3, B4, B5, B6, and B7 in different trajectories in the optical axis direction of the reduction side optical system 102. The aperture stop ST moves together with the lens group B6.

Tables 3-1 to 3-3 show various numerical values of the projection optical system according to this embodiment.

In the present embodiment, not only each single lens but also the convex reflector M21 and the concave reflector M22 have a rotationally symmetric surface shape around the optical axis as in the other embodiments, and a part thereof is cut out. It has become.

FIG. 7 shows a cross-sectional view of the reduction side optical system 102 of the projection optical system according to the present embodiment at a wide angle end (projection distance 4650 mm) and close distance (projection distance 543 mm).

In this embodiment, focusing is performed by moving the lens groups B1a, B1b, and B1c in the same direction as in the other embodiments. The amount of movement is different.

As indicated by the arrows in FIG. 7, the lens groups B1a, B1b, and B1c all move to the magnifying conjugate side during focusing from a distance to a close distance.

Similar to the other embodiments, the lens groups B1a and B1b having different sign powers are configured to move in the same direction, so that the change in the chromatic aberration of magnification during focusing is suppressed, and the curvature of field and the distortion are prevented. It enables correction.

Further, the lens group B1c is also configured to move in the same direction, which is advantageous for miniaturization.

The focal length fa of the lens group B1a, the ratio of the focal length fb of the lens group B1b, and fa / fb are −0.944 in the present embodiment, and are configured to satisfy the equation (3).

The absolute value of the power of the lens group B1c is set to be the largest among the lens groups B1a, B1b, and B1c as in the other examples, and the movement amount of the lens group B1c is reduced to suppress the fluctuation of the off-axis aberration. There is.

Further, the lens group B1c is composed of a single lens L33 having an aspherical shape on both sides, and further reduces fluctuations in off-axis aberrations.

In the present embodiment, | fc / fab | is 0.109, which is configured to satisfy the formula (5).

FIG. 8 shows longitudinal aberration diagrams at projection distances of 543 mm, 775 mm, and 4650 mm according to the present embodiment. The points to be noted in the aberration diagram are the same as in other embodiments.

Each projection distance is a close, reference, and distant projection distance, and when the aspect ratio of the projected image is 16:10, the size of the projected image is 70 inches, 100 inches, and 600 inches.

It can be seen that all the aberrations are satisfactorily corrected at each projection distance.

FIG. 9 shows chromatic aberration of magnification at projection distances of 543 mm, 775 mm, and 4650 mm in the present embodiment.

It can be seen that the chromatic aberration of magnification is satisfactorily corrected at any projection distance, and the change in chromatic aberration of magnification due to focusing is well suppressed.

The present embodiment is not limited to this, and like other embodiments, it can be changed within the scope of the gist. For example, the plane reflector for bending the optical path may be eliminated and the projection direction may be set as in the first embodiment.

[Fourth Embodiment]
FIG. 10 shows an optical path diagram of the projection optical system 100 according to the fourth embodiment.

Since this projection optical system is a zoom lens having a scaling function, FIG. 10 shows an optical path diagram at a wide-angle end at a projection distance of 775 mm.

The projection optical system 100 is composed of an expansion side optical system 101 and a reduction side optical system 102 as in other embodiments.

However, in the present embodiment, the convex reflector M31 constituting the magnifying side optical system 101 and the single lens L51 constituting the reducing side optical system 102 are integrated.

Specifically, the lower half of the single lens L51 is used as a lens in which the luminous flux is refracted, and constitutes a part of the reduction side optical system 102.

On the other hand, the upper half of the single lens L51 on the magnifying conjugate side is coated with a reflective film and used as a convex reflector M31, which constitutes a part of the magnifying optical system 101.

The magnifying side optical system 101 is composed of a convex reflector M21 having a negative power and a positive concave reflector M22 in order from the magnifying conjugate side, and has a positive power as the magnifying side optical system 101.

Similar to the third embodiment, the reduction side optical system 102 has lens groups B1, B2, B3, B4, whose powers are negative, positive, positive, positive, positive, negative, positive, and positive, respectively, in order from the expansion conjugate side. It is composed of B5, B6, B7 and B8.

For each lens group constituting the reduction side optical system 102, the lens group B1 has a positive power to move in the optical axis direction of the fixed lens group B1e and the reduction side optical system 102 during focusing due to a change in projection distance. It is composed of a lens group B1a, a lens group B1b having a negative power, and a lens group B1c having a negative power.

The lens groups B1e, B1a, B1b, and B1c are composed of single lenses L51, L52, L53, and L54, respectively, and the powers of the single lenses L51, L52, L53, and L54 are positive, positive, negative, and negative, respectively.

The lens group B2 is composed of only a single lens L55 having a positive power.

The lens group B3 is composed of only a single lens L56 having a positive power.

The lens group B4 is composed of only a single lens L57 having a positive power.

The lens group B5 is composed of a bonded lens in which a single lens L58 having a negative power and a single lens L59 having a positive power are bonded together.

The lens group B6 is composed of only a single lens L60 having a negative power.

The lens group B7 is composed of single lenses L61 and L64 having positive and positive powers, respectively, and a bonded lens in which L62 having negative power and L63 having positive power are bonded together.

The lens group B8 is composed of only a single lens L65 having a positive power.

In the present embodiment, the scaling is performed by changing the spacing of each lens group constituting the reduction side optical system 102 as in the other embodiments.

In the present embodiment, the magnification is changed by moving the six lens groups B2, B3, B4, B5, B6, and B7 in different trajectories in the optical axis direction of the reduction side optical system 102. The aperture stop ST moves together with the lens group B6.

Tables 4-1 to 4-3 show various numerical values of the projection optical system according to this embodiment.

In the present embodiment, not only each single lens but also the convex reflector M31 and the concave reflector M32 have a rotationally symmetric surface shape around the optical axis, and a part of the M32 is cut out. As described above, M31 is formed by coating a part of the surface of the single lens L51 on the enlarged conjugated side with a reflective film.

In Tables 4-1 to 4-3, the aspherical coefficients are described with both M31 and L51 as different surface numbers for convenience, but since the aspherical coefficients are the same, they have the same rotationally symmetric shape. You can see that.

FIG. 11 shows a cross-sectional view of the reduction side optical system 102 of the projection optical system according to the present embodiment at a wide angle end (projection distance 4650 mm) and close distance (projection distance 543 mm).

In this embodiment, focusing is performed by moving the lens groups B1a, B1b, and B1c in the same direction as in the other embodiments. The amount of movement is different.

As indicated by the arrows in FIG. 11, the lens groups B1a, B1b, and B1c all move to the magnifying conjugate side during focusing from a distance to a close distance.

Similar to the other embodiments, the lens groups B1a and B1b having different sign powers are configured to move in the same direction, so that the change in the chromatic aberration of magnification during focusing is suppressed, and the curvature of field and the distortion are prevented. It enables correction.

Further, the lens group B1c is also configured to move in the same direction, which is advantageous for miniaturization.

The focal length fa of the lens group B1a, the ratio of the focal length fb of the lens group B1b, and fa / fb are −1.042 in this embodiment, and are configured to satisfy the equation (3).

The absolute value of the power of the lens group B1c is set to be the largest among the lens groups B1a, B1b, and B1c as in the other examples, and the movement amount of the lens group B1c is reduced to suppress the fluctuation of the off-axis aberration. There is.

Further, the lens group B1c is composed of a single lens L33 having an aspherical shape on both sides, and further reduces fluctuations in off-axis aberrations.

In the present embodiment, | fc / fab | is 0.057, which is configured to satisfy the formula (5).

FIG. 12 shows longitudinal aberration diagrams at projection distances of 543 mm, 775 mm, and 4650 mm according to the present embodiment. The points to be noted in the aberration diagram are the same as in other embodiments.

Each projection distance is a close, reference, and distant projection distance, and when the aspect ratio of the projected image is 16:10, the size of the projected image is 70 inches, 100 inches, and 600 inches.

It can be seen that all the aberrations are satisfactorily corrected at each projection distance.

FIG. 13 shows chromatic aberration of magnification at projection distances of 543 mm, 775 mm, and 4650 mm in the present embodiment.

It can be seen that the chromatic aberration of magnification is satisfactorily corrected at any projection distance, and the change in chromatic aberration of magnification due to focusing is well suppressed.

The present embodiment is not limited to this, and like other embodiments, it can be changed within the scope of the gist.

For example, although the projection optical system has been described in all the embodiments including the present embodiment, the color synthesis optical system 200 can be changed and the light modulation element 300 can be replaced with a CCD sensor, a CMOS sensor, or the like to provide an imaging optical system. Can be used.

In addition, the back focus value and the like can be changed according to each intended use.

100 projection optical system, 101 magnifying side optical system, 102 reducing side optical system,
200 color composite optics, 300 light modulation elements, 301 intermediate image,
ST Aperture Aperture, B1 1st Lens Group, B2 2nd Lens Group,
B3 3rd lens group, B4 4th lens group, B5 5th lens group,
B6 6th lens group, B7 7th lens group, B8 8th lens group,
B1a 1st focus lens group, B1b 2nd focus lens group,
B1c 3rd focus lens group

Claims (11)

It has a reduction side optical system having a positive refractive force in order from the reduction conjugate side, and a magnifying side optical system having a positive refractive power including a reflective optical element, and an intermediate image by the reduction side optical system is displayed on the enlargement side optical system. An optical system to be reimaged, the magnifying side optical system is fixed at the time of focusing, and the reducing side optical system has at least three lens groups moving along an optical axis, and the three lens groups of the three lens groups. An optical system characterized in that the power of the lens group on the most magnifying side and the lens group on the next magnifying side have opposite signs, and the power of the lens group on the most reducing side is negative, and they move in the same direction. The optical system according to claim 1, wherein the three lens groups move to the magnifying conjugate side when focusing from a distance to a close distance. The optical system according to claim 1 or 2, wherein the lens group having the largest absolute value of power among the three lens groups is the lens group on the reduction side. The optical system according to any one of claims 1 to 3, wherein the lens group on the reduction side among the three lens groups includes at least one aspherical surface. When the focal lengths of the lens group on the most magnifying side and the next lens group among the three lens groups are set to fa and fb, respectively.
The optical system according to any one of claims 1 to 4, wherein the optical system is characterized in that. When the focal lengths of the lens group on the most magnifying side and the next lens group among the three lens groups are set to fa and fb, respectively.
The optical system according to any one of claims 1 to 4, wherein the optical system is characterized in that. When the combined focal length of the lens group on the most magnifying side and the next lens group among the three lens groups is Fab, and the focal length of the lens group on the most reducing side is fc,
The optical system according to any one of claims 1 to 6, wherein the optical system is characterized in that. When the combined focal length of the lens group on the most magnifying side and the next lens group among the three lens groups is Fab, and the focal length of the lens group on the most reducing side is fc,
The optical system according to any one of claims 1 to 6, wherein the optical system is characterized in that. The optical system according to any one of claims 1 to 8, wherein the three lens groups have positive, negative, and negative powers from the magnifying side. The optical system according to any one of claims 1 to 9, wherein the optical system has a scaling function. The optical system according to any one of claims 1 to 10, wherein the magnifying side optical system includes at least concave and convex mirrors.