Patent Grant
12007539
The present disclosure relates to a projection lens system in which an image on a reduction side is projected on a magnification side, and an image projection device including the projection lens system.
JP 2011-053663 A discloses an optical system for satisfactorily correcting chromatic aberration in an image projection device and an imaging device and suppressing a shift in focus position due to a temperature change. In the optical system of JP 2011-053663 A, at least two positive lenses in which the Abbe number, the anomalous dispersion, the rate of change in refractive index with respect to temperature changes, etc. are set in appropriate ranges are provided closer to the reduction side than a diaphragm. As a result, while the width of the axial luminous flux is increased to favorably correct the axial chromatic aberration, the shift of the focus position caused by the change in the refractive index due to the temperature change is suppressed. JP 2011-053663 A cites a lamp used as a light source as a cause of high temperature in an image projection device.
The present disclosure provides a projection lens system and an image projection device that can reduce axial chromatic aberration and improve the image quality of an image when the brightness of the image projection device is increased, particularly with a long focus lens.
A projection lens system of the present disclosure is a projection optical system including a plurality of lens groups, the plurality of lens groups each including one or more lenses and moving such that an interval between the lens groups changes during a zooming action,
the projection lens system including a first lens group disposed closest to a magnification side, the first lens group having positive power,
wherein the first lens group includes one negative lens satisfying following conditions (1) and (2):
0.0005<Δpgfn<0.01 (1)
32<vdn<45 (2)
where
Δpgfn=(ngn−nfn)/(nfn−ncn)−(−2.20599×10−3×vdn+6.69612×10−1),
vdn is Abbe number of negative lens,
ngn is a refractive index of the negative lens to g-line,
nfn is a refractive index of the negative lens to F-line, and
ncn is a refractive index of the negative lens to C-line.
According to the projection lens system and the image projection device of the present disclosure, it is possible to reduce axial chromatic aberration and improve an image quality of an image when brightness of the image projection device is increased.
Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed descriptions of already well-known matters or duplicate descriptions of substantially the same configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art.
It should be noted that the applicant provides the accompanying drawings and the following description so that those skilled in the art can sufficiently understand the present disclosure, and they are not intended to limit the subject matter set forth in the claims.
fm=√{square root over ((fW*fT))} [Equation 1]
In addition, in
In each longitudinal aberration diagram, a spherical aberration diagram, an astigmatism diagram, and a distortion diagram are shown in order from the left side. In the spherical aberration diagram, the lateral axis represents spherical aberration (SA (mm)), and the vertical axis represents F-number (marked with F in the drawing). In the spherical aberration diagram, the solid line, short-dash line, and long-dash line represent the characteristics of d-line, F-line, and C-line, respectively. In the astigmatism diagram, the lateral axis represents the astigmatism (AST mm), and the vertical axis represents an image height (marked with H in the drawing). In the astigmatism diagram, the solid line shows the characteristics of sagittal plane (marked with s in the drawing), and the broken line shows the characteristics of meridional plane (marked with m in the drawing). In the distortion diagram, the lateral axis represents a distortion (DIS (%)), and the vertical axis represents an image height (marked with H in the drawing).
In the following embodiments, as illustrated in
The projection lens system of the present disclosure includes first lens group G1 having positive power, second lens group G2 having negative power, and third lens group G3 having positive power in this order from the magnification side to the reduction side.
First lens group G1 includes, in order from the magnification side to the reduction side, first lens L1 which is negative meniscus with a convex surface placed toward the magnification side, second lens L2 which is positive meniscus with a convex surface placed toward the magnification side, and third lens L3 which is biconvex.
Second lens group G2 includes, in order from the magnification side to the reduction side, fourth lens L4 which is positive meniscus with a convex surface placed toward the magnification side, fifth lens L5 which is negative meniscus with a convex surface placed toward the magnification side, sixth lens L6 which is biconcave, seventh lens L7 which is biconcave, and eighth lens L8 which is positive meniscus with a convex surface placed toward the magnification side.
Third lens group G3 is composed of aperture diaphragm A and lenses from ninth lens L9 to sixteenth lens L16. Third lens group G3 includes, in order from the magnification side to the reduction side, ninth lens L9 which is biconvex, tenth lens L10 which is negative meniscus with a convex surface placed toward the reduction side, eleventh lens L11 which is biconvex, twelfth lens L12 which is biconcave, thirteenth lens L13 which is biconvex, fourteenth lens L14 which is biconcave, fifteenth lens L15 which is biconvex, and sixteenth lens L16 which is biconvex.
Optical element P is disposed between third lens group G3 and original image S.
When the imaging optical system zooms from the wide angle end to the telephoto end, first lens group G1 is relatively fixed with respect to an image plane of original image S. Second lens group G2 simply moves toward the reduction side with respect to the image plane of original image S. Third lens group G3 moves toward the magnification side with respect to the image plane of original image S.
All lens groups move to the magnification side along the optical axis during an action of focusing from an infinite focus state to a proximate focus state.
The projection lens system of the present embodiment is a projection lens system having a plurality of lens groups that include one or more lenses and that move such that the interval between the lens groups changes during a zooming action. The projection lens system includes first lens group G1 with positive power disposed closest to the magnification side, and has one negative lens in first lens group G1. The conditions satisfied by the projection lens system are shown below.
The negative lens of the projection lens system of the present disclosure satisfies following condition (1):
0.0005<Δpgfn<0.01 (1)
where
Δpgfn=(ngn−nfn)/(nfn−ncn)−(−2.20599×10−3×vdn+6.69612×10−1),
vdn is Abbe number of negative lens,
ngn is a refractive index of negative lens for g-line,
nfn is a refractive index of negative lens for F-line, and
ncn is a refractive index of negative lens for C-line.
Condition (1) prescribes the partial dispersion ratio between the g-line and the F-line of the negative lens in first lens group G1. At high brightness, performance degradation occurs due to the influence of lens shape change. In order to suppress the performance degradation, a positive lens is provided with a glass material having a negative temperature coefficient, which has an effect opposite to the effect of the shape change. However, the negative temperature coefficient glass material is a so-called anomalous dispersion glass. In the long focus lens in particular, the width of the light ray with respect to the effective diameter is wide, and thus many lenses affect the performance degradation due to the lens shape change. Then, the number of positive anomalous dispersion glasses to be used increases. Then, it becomes difficult to correct the axial chromatic aberration of each wavelength. Therefore, satisfying condition (1) makes it possible to suppress axial chromatic aberration at each wavelength adequately. Falling below a lower limit of condition (1) causes increase in axial chromatic aberration at wide angle end. On the other hand, excess over an upper limit of condition (1) causes increase in axial chromatic aberration at telephoto end.
The imaging optical system of the present disclosure satisfies following condition (2).
32<vdn<45 (2)
Condition (2) prescribes the Abbe number of the negative lens in first lens group G1. By satisfying condition (2), axial chromatic aberration can be suppressed. Falling below a lower limit of condition (2) causes axial chromatic aberration on the short wavelength side over, so that the axial chromatic aberration increases. On the other hand, excess over an upper limit causes axial chromatic aberration on the short wavelength side under, so that the axial chromatic aberration increases.
The projection lens system of the present disclosure satisfies following condition (3):
0.8<|fn/f1|<1.5 (3)
where
fn is a focal length of the negative lens in first lens group G1, and
f1 is a focal length of first lens group G1.
Condition (3) prescribes the focal length of the negative lens in first lens group G1. Satisfaction of condition (3) can achieve this advantage: correcting spherical aberration. Falling below a lower limit of condition (3) causes spherical aberration under, so that it becomes impossible to sufficiently correct the spherical aberration. On the other hand, excess over an upper limit causes spherical aberration over, so that it becomes impossible to sufficiently correct the spherical aberration.
Satisfaction of the following condition (3a) can more positively achieve the foregoing advantage.
1.0<|fn/f1|<1.3 (3a)
The projection lens system of the present disclosure satisfies following condition (4):
1.0<f1/ft<2.0 (4)
where ft is a focal length at telephoto end when projection distance is infinity.
Condition (4) prescribes the focal length of first lens group G1. Satisfaction of condition (4) can achieve this advantage: reducing the total length and suppressing spherical aberration. Excess over an upper limit of condition (4) causes increase in the total length. On the other hand, falling below a lower limit causes generation of spherical aberration.
Satisfaction of the following condition (4a) can more positively achieve the foregoing advantage.
1.2<f1/ft<1.6 (4a)
In the projection lens system of the present disclosure, first lens group G1 has at least one positive lens and satisfies following condition (5):
dn1/dt<−4.5×10−6 (5)
where dn1/dt is a refractive index-temperature coefficient of a material of the positive lens of first lens group G1 at normal temperature. The normal temperature is 20° C. to 30° C., for example.
Condition (5) prescribes the refractive index-temperature coefficient. Excess over an upper limit of condition (5) causes difficulty in cancelling out the influence of shape change and the influence of changes in the refractive index, for example in a case of the focus position shift due to local temperature change arising at high brightness, so that focusing sensitivity shifts during high brightness.
The projection lens system of the present disclosure has second lens group G2 disposed closer to the reduction side of first lens group G1, and second lens group G2 has positive power and satisfies following condition (6):
0.2<|f2/ft|<0.7 (6)
where f2 is a focal length of second lens group G2.
Condition (6) prescribes the focal length of second lens group G2. Satisfaction of condition (6) can achieve this advantage: shortening the total length and reducing the sensitivity to eccentricity. Excess over an upper limit of condition (6) causes increase in the total length. On the other hand, falling below a lower limit of condition (6) causes increase in the sensitivity of second lens group G2 to eccentricity.
Satisfaction of the following condition (6a) can more positively achieve the foregoing advantage.
0.3<|f2/ft|<0.6 (6a)
The projection lens system of the present disclosure has third lens group G3 disposed closer to the reduction side of second lens group G2, and third lens group G3 has positive power and satisfies following condition (7):
0.3<f3/ft<1.0 (7)
where f3 is a focal length of third lens group G3.
Condition (7) prescribes the focal length of third lens group G3. Satisfaction of condition (7) can achieve this advantage: reducing the total length and reducing the sensitivity to eccentricity. Falling below a lower limit of condition (7) causes increase in the sensitivity to eccentricity. On the other hand, excess over an upper limit causes increase in the total length.
Satisfaction of the following condition (7a) can more positively achieve the foregoing advantage.
0.5<f3/ft<0.8 (7a)
In the projection lens system of the present disclosure, the positive lens is disposed closest to the magnification side of second lens group G2 and satisfies following condition (8):
0.0005<Δpgfp<0.01 (8)
where
Δpgfp=(ngp−nfp)/(nfp−ncp)−(−2.20599×10−3×vdp+6.69612×10−1),
vdp is Abbe number of negative lens,
ngp is a refractive index of negative lens for g-line,
nfp is a refractive index of negative lens for F-line, and
ncp is a refractive index of negative lens for C-line.
Condition (8) prescribes a partial dispersion ratio between the g-line and the F-line of the positive lens disposed closest to the magnification in second lens group G2. Satisfaction of condition (8) can achieve this advantage: suppressing axial chromatic aberration. Falling below a lower limit of condition (8) causes invite increase in axial chromatic aberration at telephoto end. On the other hand, excess over an upper limit of condition (8) causes increase in the axial chromatic aberration at wide angle end.
The projection lens system of the present disclosure satisfies following condition (9).
32<vdp<45 (9)
Condition (9) prescribes the Abbe number of the positive lens disposed closest to the magnification side in second lens group G2. Satisfaction of condition (9) can achieve this advantage: suppressing axial chromatic aberration. Falling below a lower limit of condition (9) causes generation of axial chromatic aberration on the short wavelength side under, so that the axial chromatic aberration increases. On the other hand, excess over an upper limit causes excess generation of axial chromatic aberration on the short wavelength side, so that the axial chromatic aberration increases.
In the projection lens system of the present disclosure, at least five positive lenses are included in third lens group G3, and at least five positive lenses satisfy following condition (10):
dn3/dt<−4.5×10−6 (10)
where dn3/dt is a refractive index-temperature coefficient of a material of the positive lens of third lens group G3 at normal temperature. The normal temperature is 20° C. to 30° C., for example.
Condition (10) prescribes the temperature coefficient of refractive index. Excess over an upper limit of condition (10) causes difficulty in cancelling out the influence of shape change and the influence of changes in the refractive index, for example in a case of the focus position shift due to local temperature changes arising at high brightness, so that focusing sensitivity shifts during high brightness.
As described above, the embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments in which changes, substitutions, additions, omissions, and the like have been made as appropriate.
Embodiments with numerical simulation of imaging optical systems of the first to third embodiments will be described below. In each embodiment with numerical simulation, all units of length in the table are “mm” and all units of angle of view are “°”. In each embodiment with numerical simulation, r is curvature radius, d is spacing between adjacent surfaces, nd is a refractive index with respect to d line, and vd is Abbe number with respect to d line.
The lens data of the first embodiment are shown in Tables 1 to 3. Table 1 shows surface data. Table 2 shows various data. Table 3 shows zoom group data and single lens data.
Lens data of the second embodiment are shown in Tables 4 to 6. Table 4 shows surface data. Table 5 shows various data. Table 6 shows zoom group data and single lens data.
Lens data of the third embodiment are shown in Tables 7 to 9. Table 7 shows surface data. Table 8 shows various data. Table 9 shows zoom group data and single lens data.
The following Table 10 shows corresponding values for each condition in the lens system of each embodiment with numerical simulation.
The present disclosure can be applied to an image projection device such as a projector, a digital still camera, a digital video camera, a surveillance camera in a surveillance system, a web camera, and a vehicle-mounted camera. The present disclosure is applicable particularly to an imaging optical system that requires high image quality such as a projector, a digital still camera system, and a digital video camera system.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-183756 | Sep 2018 | JP | national |
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| Number | Date | Country |
|---|---|---|
| 2011-53663 | Mar 2011 | JP |
| 2014-106391 | Jun 2014 | JP |
| 2014-126766 | Jul 2014 | JP |
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| Entry |
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| Extended European Search Report dated Oct. 25, 2021 in corresponding European Patent Application No. 19864149.0. |
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| Number | Date | Country | |
|---|---|---|---|
| 20210116688 A1 | Apr 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2019/035494 | Sep 2019 | WO |
| Child | 17113376 | US |
