JP2013003297A - Projection lens and projection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact projection lens whose various aberrations are excellently corrected, in which when an image is obliquely projected in a projection device, a one-sided blur is generated by the eccentricity of the lens group of an optical system, to correct a focus and to provide the projection device.SOLUTION: When detection means TS detects the inclination of a projection device PJ, a signal corresponding to the detected inclination is outputted to a controller CONT. The controller CONT decides a lens shift amount to properly correct the blur of the image, according to the inclination of the projection device PJ and relatively shifts (decenters) a first lens group G1 and a second lens group in a direction orthogonal to an optical axis through a lens drive device DR. Thus, even when the projection device PJ is inclined, the blur of the image projected onto a screen SC can be suppressed.

Description

  The present invention relates to a small-sized projection lens and a projection apparatus that can correct a focus shift that occurs during oblique projection and have high optical performance.

  When a projection device such as a projector is installed on a table such as a desk, if the projection device and the screen are directly facing each other, depending on the arrangement, the projection image may be blocked by the table such as the desk or the observation may be obstructed. Will approach the grounding surface, causing problems such as poor visibility from a plurality of observers. One means for avoiding this is to tilt the optical axis of the projection device upward to shift the projected image from the ground plane to a higher direction. However, if the optical axis of the projection apparatus is tilted, problems arise such that the focus position of the projected image is shifted from the screen, or the image is distorted due to the occurrence of trapezoidal distortion. Among these, an example of means for avoiding / correcting the focus position deviation is disclosed in Patent Document 1 below.

Japanese Patent Laid-Open No. 5-241096

Yoshinori Hayami, “Optics I of Optical Equipment”, Japan Opto-Mechatronics Association, pages 64 to 69

  However, in the technique of Patent Document 1, it is necessary to move the second lens group and the liquid crystal panel (light valve) separately, which complicates the mechanism. Further, when trying to satisfy the Scheimpflug condition as described in Non-Patent Document 1, the screen (enlarged side) is non-inclined to cross the object plane, image plane, and lens main surface on the same straight line. In the case of fixing, it is necessary to tilt the lens system and the light valve (reduction side) separately, which complicates the mechanism and enlarges the apparatus.

  The present invention has been made in view of such problems, and realizes focus correction by generating one-sided blur due to the eccentricity of the lens group of the optical system when an image is projected obliquely in the projection apparatus. The present invention provides a projection lens and a projection apparatus that are small and have various aberrations corrected satisfactorily.

  The projection lens according to claim 1 is a projection lens for a projection device that magnifies an image and projects it on a screen, in order from the magnification side, a negative first lens group, a positive second lens group, The first lens group and the second lens group are relatively deviated from the out-of-focus on the screen, which is generated when the optical axis is inclined with respect to the screen. It is characterized by correcting by making the core.

  According to the present invention, since it is possible to focus by decentering only the first lens group and the second lens group without moving the entire optical system or the light valve, a high-quality image can be projected. Nevertheless, the apparatus and mechanism can be simplified with a small number of moving parts.

  According to a second aspect of the present invention, there is provided the projection lens according to the first aspect, wherein each of the first lens group and the second lens group includes at least one positive lens and one negative lens. And

  As a result, the intra-group aberration is corrected better than when the first lens group and the second lens group are each composed of a single lens. It can be suppressed.

  According to a third aspect of the present invention, there is provided the projection lens according to the first or second aspect, wherein the first lens group includes, in order from the enlargement side, a first lens having a negative refractive power and a first lens having a positive refractive power. The second lens group consists of a second lens, a fourth lens having a negative refractive power, a fifth lens having a positive refractive power, and a sixth lens having a positive refractive power. An aperture stop is provided between the first lens group and the second lens group, and the third lens group is composed of one positive lens.

  By using a negative lens for the first lens, a long back focus can be secured, and a polarizing beam splitter (PBS) or wire grid is installed, which is necessary when using a liquid crystal member such as LCOS for the light valve. Space can be secured. Further, by arranging the second lens to the fifth lens in a positive / negative / negative manner with an aperture stop interposed therebetween, symmetry can be improved and good aberration correction can be performed. In addition, the positive lens of the fifth lens has an effect of converging the light beam and suppressing the optical total length and the effective diameter to be small. Further, by arranging the third lens group as one positive lens and being arranged in the vicinity of the light valve, it is possible to secure good telecentricity on the reduction side with a minimum number of condenser lenses, and from the first lens group, It becomes possible to reduce the lens diameter of the second lens group.

  According to a fourth aspect of the present invention, in the invention according to the third aspect, the second lens and the third lens are cemented with each other.

  The chromatic aberration and spherical aberration in the first lens group are corrected well, and the number of component elements when the lens is incorporated into the holding mechanism is reduced, so that the assemblability is improved.

  According to a fifth aspect of the present invention, in the invention according to the third or fourth aspect, the fourth lens and the fifth lens are cemented with each other.

  The chromatic aberration and spherical aberration in the second lens group are corrected well, and the number of component elements when the lens is incorporated into the holding mechanism is reduced, so that the assemblability is improved.

A projection lens according to a sixth aspect of the present invention is the projection lens according to any one of the first to fifth aspects, wherein the first lens group satisfies the following conditional expression.
-3.0 <f1 / f <-1.0 (1)
However,
f1: Composite focal length of the first lens group
f: Focal length of the entire projection lens system

  If the value of conditional expression (1) does not exceed the lower limit, the optical system can be kept downsized. On the other hand, if the upper limit is not exceeded, reduction in contrast when the first lens unit is decentered can be suppressed. Various aberrations occurring in the lens group can be suppressed.

A projection lens according to a seventh aspect is characterized in that, in the invention according to any one of the first to sixth aspects, the second lens group satisfies the following conditional expression.
1.0 <f2 / f <2.0 (2)
However,
f2: Composite focal length of the second lens group
f: Focal length of the entire projection lens system

  If the value of conditional expression (2) does not exceed the lower limit, the optical system can be kept downsized. On the other hand, if the upper limit is not exceeded, the decrease in contrast when the second lens group is decentered can be suppressed, or the second lens group can be reduced. Can suppress various aberrations.

According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the first lens group and the second lens group satisfy the following conditional expression.
-2.0 <f1 / f2 <-0.5 (3)
However,
f1: Composite focal length of the first lens group f2: Composite focal length of the second lens group

  If the value of conditional expression (2) does not exceed the lower limit, the back focus necessary for arranging the polarizing beam splitter and the wire grid can be secured, and on the other hand, the upper limit is not incurred without exceeding the upper limit. It will end.

Here, the decentration aberration coefficient will be described.
《Derivation of decentration aberration by aberration coefficient》
When a part of the optical system (for example, a surface, a lens, or a lens group) is displaced or tilted in a direction perpendicular to the optical axis (that is, when an eccentric error such as parallel eccentricity or tilt eccentricity occurs) The optical performance deteriorates due to the eccentricity. This is because decentration aberrations occur in the optical system due to decentration. The error sensitivity of this decentration aberration is one factor that makes it difficult to manufacture an optical system. The main decentration aberrations are the one-sided blur aberration and the axial coma aberration.

  The “single blur aberration” is a phenomenon in which the image plane becomes asymmetric with respect to the optical axis. That is, a phenomenon in which the image plane position differs between a positive field angle and a negative field angle due to occurrence of eccentricity. The half-blurring aberration is usually evaluated by an average value of the difference in the paraxial image plane position of the principal ray having a field angle of about 70% of the screen diagonal. On the other hand, “axial coma” is a phenomenon in which an axial light beam becomes asymmetric with respect to the principal ray. According to an optical system that should be rotationally symmetric, the point image on the axis is also usually rotationally symmetric. However, if eccentricity occurs in a part of the optical system, the symmetry is lost and the image performance is greatly deteriorated. Axial coma is usually the difference between the average ray position of the upper zonal ray (Upper) and the lower zonal ray (Lower) on the axis whose diameter is about 70% of the effective diameter on the axis and the axial principal ray position. Be evaluated. In the following, aberrations of an optical system with decentration are studied, and the above two decentration aberrations are derived using an aberration coefficient.

<Third-order aberration expansion formula for optical systems with decentration>
FIG. 1 shows the relationship between the basic optical system and coordinates. 1 (a) and 1 (b), OS is the object plane, IS is the image plane, PS1 is the entrance pupil plane, PS2 is the exit pupil plane, HS1 is the object side principal plane (H: object side principal point), and HS2 is Image-side principal plane (H ′: image-side principal point), SF is the front surface of the optical system, SR is the rear surface of the optical system, N is the refractive index in object space, and N ′ is the refractive index in image space.

The optical axis of the optical system when there is no eccentricity is taken as a reference axis AX, which is taken as the X axis, and the Y axis and Z axis are taken perpendicularly thereto. Then, the coordinates of the object point OP are (Y, Z), the coordinates of the incident point of the light ray on the entrance pupil plane PS1 are (Y *, Z *), and the coordinates of the image space corresponding to these are “'”. Represent it. However, when the lateral aberration of the light beam on the image plane IS is expanded to a third-order power series, the following polar coordinates are defined as the coordinates of the object point OP and the incident point of the light beam on the entrance pupil plane PS1.
tanω · cosφω≡Y / g $ (1A)
tanω · sinφω≡Z / g $ (1B)
R · cosφR≡ (g $ / g) · Y * (2A)
R · sinφR≡ (g $ / g) · Z * (2B)

  As can be seen from FIG. 1, g and g $ are the entrance pupil plane PS1, the distance from the object-side principal plane HS1 to the object plane OS, and ω is the straight line connecting the object point OP and the object-side principal point H is the reference axis AX Is the azimuth angle (azimuth), R is the entrance pupil radius converted on the object-side main plane HS1, and φR is the azimuth angle. "'" Represents the image space, and "#" represents the off-axis principal ray, so α is the conversion angle of the paraxial off-axis marginal ray in the object space, and α # is the conversion of the paraxial off-axis principal ray in the object space. The tilt angle, α ′, is a converted tilt angle in the image space of the paraxial off-axis marginal ray, and α ′ # is a converted tilt angle in the image space of the paraxial off-axis principal ray.

  Assuming that the optical system is composed of k elements, the lateral aberrations ΔY ′ and ΔZ ′ are expressed in the following equations (3A) and (3B) when the lateral aberration when decentration exists is expanded to a power series. (Β: lateral magnification). The third-order aberration coefficients corresponding to spherical aberration, coma aberration, astigmatism, Petzval sum and distortion aberration are I, II, III, P and V, respectively, and the index μ is an element number, and α ′ = α ′ k, α ′ # = α ′ # k. The display using the summation symbol Σ is performed as shown in the following example (the same applies hereinafter).

ΔY′≡Y′−β · Y = − [1 / (2 · α ′)] · {(N · tan ω) ³ · cos φω · (μ = 1 → k) ΣVμ + R · (N · tan ω) ² · [ 2 · cos (φR-φω) · cosφω · (μ = 1 → k) ΣIIIμ + cosφR · (μ = 1 → k) Σ (IIIμ + Pμ)] + R 2 · (N · tanω) · [2 · cosφR · cos (φR −φω) + cos φω] · (μ = 1 → k) ΣIIμ + R ³ · cosφR · (μ = 1 → k) ΣIμ} + {additional term due to eccentricity (Y component)} (3A) ΔZ′≡Z′−β Z = − [1 / (2 · α ′)] · {(N · tan ω) ³ · sin φω · (μ = 1 → k) ΣVμ + R · (N · tan ω) ² · [2 · cos (φR−φω ) · sinφω · (μ = 1 → k) ΣIIIμ + sinφR · (μ = 1 → k) Σ (IIIμ + Pμ)] + R 2 · (N · tanω) · [2 · sinφR · c s (φR-φω) + sinφω ] · (μ = 1 → k) ΣIIμ + R 3 · sinφR · (μ = 1 → k) ΣIμ} + { added by an eccentric section (Z component)} ... (3B)

  In these formulas (3A) and (3B), the first {} in the right side is a term representing the original aberration of the optical system when there is no decentration. If decentration exists, the aberration term generated by decentration is It becomes a form to join. When an arbitrary element in the optical system (which may be a single surface or a composite system composed of a plurality of surfaces) is decentered, the decentering is in a direction perpendicular to the reference axis AX of the optical system. There are "parallel eccentricity" that translates and "tilt eccentricity" that tilts with respect to the reference axis AX. Both of these effects are expressed as an additional term on the right side of the above formulas (3A) and (3B).

<Derivation of parallel decentration aberration coefficient>
FIG. 2A shows an arbitrary ν-th element in the optical system (hereinafter referred to as “the ν-element”, the optical axis of the ν-element is represented by AXν) Dν with respect to the reference axis AX of the optical system. In the vertical Y direction, a state of being decentered by a minute amount Eν is shown. Additional terms ΔY (Eν) and ΔZ (Eν) of the aberration coefficient due to the parallel decentering are expressed by the following equations (4A) and (4B).

ΔY (Eν) = − [Eν / (2 · α′k)] · {(ΔE) ν + (N · tanω) ² · [(2 + cos2φω) · (VE1) ν− (VE2) ν] + 2 · R · (N · tanω) · [(2 · cos (φR−φω) + cos (φR + φω)) · (IIIE) ν + cosφR · cosφω · (PE) ν] + R ² · (2 + cos2φR) · (IIE) ν} (4A )
ΔZ (Eν) = − [Eν / (2 · α′k)] · {(N · tan ω) ² · sin 2φω · (VE1) ν + 2 · R · (N · tan ω) · [sin (φR + φω) · (IIIE ) Ν + sinφR · cosφω · (PE) ν] + R ² · sin2φR · (IIE) ν} (4B)

However, the decentration aberration coefficient is defined by the following equations (4C) to (4H).
(ΔE) ν = −2 · (α′ν−αν) (4C)
(VE1) ν = {[α′ν · (μ = ν + 1 → k) ΣVμ] − [αν · (μ = ν → k) ΣVμ]} − {[α ′ # ν · (μ = ν + 1 → k) ΣIIIμ ]-[Α # ν · (μ = ν → k) ΣIIIμ]} (4D)
(VE2) ν = [α ′ # ν · (μ = ν + 1 → k) ΣPμ] − [α # ν · (μ = ν → k) ΣPμ] (4E)
(IIIE) ν = {[α′ν · (μ = ν + 1 → k) ΣIIIμ] − [αν · (μ = ν → k) ΣIIIμ]} − {[α ′ # ν · (μ = ν + 1 → k) ΣIIμ ]-[Α # ν · (μ = ν → k) ΣIIμ]} (4F)
(PE) ν = [α′ν · (μ = ν + 1 → k) ΣPμ] − [αν · (μ = ν → k) ΣPμ] (4G)
(IIE) ν = {[α′ν · (μ = ν + 1 → k) ΣIIμ] − [αν · (μ = ν → k) ΣIIμ]} − {[α ′ # ν · (μ = ν + 1 → k) ΣIμ ]-[Α # ν · (μ = ν → k) ΣIμ]} (4H)

The decentration aberration coefficients of the above formulas (4C) to (4H) represent the influence of decentration, and each serves to represent an imaging defect having the following contents. Further, as can be seen from the equations (4A) and (4B), the amount of eccentricity Eν is applied to the entire right side, so the amount of aberration caused by the eccentricity is proportional to Eν.
(ΔE) ν: Prism action (image lateral shift).
(VE1) ν, (VE2) ν: rotationally asymmetric distortion.
(IIIE) ν, (PE) ν: rotationally asymmetric astigmatism, image plane tilt.
(IIE) ν: rotationally asymmetric coma that also appears on the axis.

  Equations (4A) to (4H) show the case where only the ν-th element Dν is decentered in parallel, but if this ν-th element Dν is composed of a single plane, a plurality of planes i to j are decentered in parallel. In this case (that is, when the decentered lens group is composed of the i-th surface to the j-th surface), the decentering amounts Ei to Ej of the decentered surfaces i to j are equal, and therefore the equation: (ΔE) i to j = ( As shown by ν = i → j) Σ [−2 · (α′ν−αν)], the aberration coefficient can be treated as a sum. Then, from α′ν = αν + 1, the equation: (ΔE) i to j = −2 · (α′j−αi) is obtained.

  Similarly, the term in the middle of Σ disappears for other aberration coefficients. For example, in PE, (PE) i to j = (ν = i → j) Σ [α′ν · (μ = ν + 1 → k) ΣPμ−αν · (μ = ν → k) ΣPμ] = α′j · ( μ = j + 1 → k) ΣPμ−αi (μ = i → k) ΣPμ = (α′j−αi) (μ = j + 1 → k) ΣPμ−αi (μ = i → j) ΣPμ = (α ′ j−αi) · (P) R−αi · (P) D where (P) R = (μ = j + 1 → k) ΣPμ: image side from a decentered lens group (hereinafter also referred to as “decentered group”). (P) D = (μ = i → j) ΣPμ: sum of aberration coefficients P of the decentered group, a group of all lens surfaces located at (hereinafter also referred to as “image side group”) It is. Accordingly, Σ of the decentration aberration coefficient is expressed by the sum {() R of the aberration coefficients of the image side group. } And the sum of the aberration coefficients of the decentration group {() D. }.

[Single-bokeh aberration]
Next, the one-sided blur will be described. From the equations (4A) and (4B), the meridional of astigmatism is [ΔY ′ (first-order term of R) φR = 0] × g ′ $ k, and the sagittal is [ΔZ ′ (first-order term of R ) ΦR = π / 2] × g ′ $ k. Therefore, the meridional piece blur ΔMν is expressed by the following equation (5A). Here, Equation (5B) is obtained from α′k = N′k / g ′ $ k and φω = 0.

ΔMν = − [Eν · g ′ $ k / (2 · α′k)] · 2 · (N · tanω) · [(2 · cos (φω) + cos (φω)) · (IIIE) ν + cos (φω) · (PE) v] (5A)
ΔMν = −Eν · (g ′ $ k ² / N′k) · (N · tan ω) · [3 · (IIIE) ν + (PE) ν] (5B)

Assuming that the object point OP is at infinity, g '$ k → FL (FL: focal length of the entire system) and N · tanω = Y ′ / FL (Y ′: image height), so the meridional one-sided blur ΔM ”ν is represented. Equation (5C) is obtained. Similarly, equation (5D) representing sagittal piece blur ΔS ″ ν is obtained.
ΔM ″ ν = −Eν · FL · Y ′ · [3 · (IIIE) ν + (PE) ν] (5C)
ΔS ″ ν = −Eν · FL · Y ′ · [(IIIE) ν + (PE) ν] (5D)

The above is the case where the ν-th surface is decentered, but when the lens group (comprising the i-th surface to the j-th surface) is decentered, Σ is taken to obtain a meridional one-sided blur (ΔM ") i to j, Expressions (5E) and (5F) representing sagittal blur (ΔS ″) i to j are obtained. Here, E is the amount of eccentricity.
(ΔM ″) i˜j = −E · FL · Y ′ · [3 · (IIIE) i˜j + (PE) i˜j] (5E)
(ΔS ″) i˜j = −E · FL · Y ′ · [(IIIE) i˜j + (PE) i˜j] (5F)

However, the decentration aberration coefficient of the block (lens group) is expressed for each of the meridional and sagittal by the following equations (5G) and (5H).
[3 · (IIIE) i˜j + (PE) i˜j] = (α′j−αi) · [3 · (III) R + (P) R] −αi · [3 · (III) D + (P) D] − (α ′ # j−α # i) · [3 · (II) R] + α # i · [3 · (II) D] (5G)
[(IIIE) i˜j + (PE) i˜j] = (α′j−αi) · [(III) R + (P) R] −αi · [(III) D + (P) D] − (α ′ # J−α # i) · [(II) R] + α # i · [(II) D] (5H)

[Axial coma]
Next, axial coma will be described. As described above, the on-axis coma aberration is an average value of the difference between the upper and lower principal ray positions of the on-axis light. Therefore, the axial coma (AXCM) ν shown in {(6A), (6B)} and Equation (6C) is derived from the Upper coma (ΔYU) ν and the Lower coma (ΔYL) ν due to the eccentricity.
(ΔYU) ν = (ΔY) (ω = 0, φR = 0) − (ΔY) (ω = 0, R = 0) = − [Eν / (2 · α′k)] · R ² · 3 · ( IIE) v (6A)
(ΔYL) ν = (ΔY) (ω = 0, φR = π) − (ΔY) (ω = 0, R = 0) = − [Eν / (2 · α′k)] · R ² · 3 · ( IIE) v (6B)
(AXCM) ν = [(ΔYU ) ν + (ΔYL) ν] / 2 = - [Eν / (2 · α'k)] · R 2 · 3 · (IIE) ν ... (6C)

If the object point is at infinity, 1 / α'k → -FL. Further, the relationship between R and FNO (the F number of the entire system) is an expression: R = [FL / (2 · FNO)] × κ (where κ is the pupil division ratio, which is usually 0.7). expressed. Therefore, the axial coma aberration (AXCM ") ν is expressed by Expression (6D).
(AXCM ″) ν = Eν · (3 · κ ² · FL ³ ) / (8 · FNO ² ) · (IIE) ν (6D)

The above is the case where the ν-th surface is decentered. However, when the lens group (comprising the i-th surface to the j-th surface) is decentered, Σ is taken to obtain equation (6E). However, the decentration aberration coefficient of the block is expressed by Expression (6F).
(AXCM ″) i˜j = E · [(3 · κ ² · FL ³ ) / (8 · FNO ² )] · (IIE) i to j (6E)
(IIE) i to j = (α′j−αi) · (II) R−αi · (II) D− (α ′ # j−α # i) · (I) R + α # i · (I) D (6F)

<Derivation of tilt decentration aberration coefficient>
FIG. 2B shows a state in which the ν-th element Dν is inclined by an angle εν around the point C with respect to the reference axis AX of the optical system. The additional terms ΔY (εν) and ΔZ (εν) of the aberration coefficient due to the tilt decentering are expressed by the following equations (7A) and (7B). The distances from the point C to the entrance pupil plane PS1 and object plane OS of the νth element Dν; the corresponding exit pupil plane PS2 and image plane IS are pν, qν; p′ν, q′ν, respectively. .

ΔY (εν) = − [εν / (2 · α′k)] · {(Δε) ν + (N · tanω) ² · [(2 + cos2φω) · (Vε1) ν− (Vε2) ν] + 2 · R · (N · tanω) · [(2 · cos (φR−φω) + cos (φR + φω)) · (IIIε) ν + cosφR · cosφω · (Pε) ν] + R ² · (2 + cos2φR) · (IIε) ν} (7A )
ΔZ (εν) = − [εν / (2 · α′k)] · {(N · tanω) ² · sin2φω · (Vε1) ν + 2 · R · (N · tanω) · [sin (φR + φω) · (IIIε ) Ν + sinφR · cosφω · (Pε) ν] + R ² · sin2φR · (IIε) ν} (7B)

However, the decentration aberration coefficient is defined by the following equations (7C) to (7H).
(Δε) ν = −2 · (α′ν · q′ν−αν · qν) (7C)
(Vε1) ν = {[α′ν · q′ν · (μ = ν + 1 → k) ΣVμ] − [αν · qν · (μ = ν → k) ΣVμ]} − {[α ′ # ν · p ′ ν · (μ = ν + 1 → k) ΣIIIμ] − [α # ν · pν · (μ = ν → k) ΣIIIμ]} + [(α ′ # ν / N′ν) − (α # ν / Nν)] ... (7D)
(Vε2) ν = {[α ′ # ν · p′ν · (μ = ν + 1 → k) ΣPμ] − [α # ν · pν · (μ = ν → k) ΣPμ]} + [(α ′ # ν / N′ν) − (α # ν / Nν)] (7E)
(IIIε) ν = {[α′ν · q′ν · (μ = ν + 1 → k) ΣIIIμ] − [αν · qν · (μ = ν → k) ΣIIIμ]} − {[α ′ # ν · p ′ ν · (μ = ν + 1 → k) ΣIIμ] − [α # ν · pν · (μ = ν → k) ΣIIμ]} (7F)
(Pε) ν = {[α′ν · q′ν · (μ = ν + 1 → k) ΣPμ] − [αν · qν · (μ = ν → k) ΣPμ]} + [(α′ν / N′ν )-(Αν / Nν)] (7G)
(IIε) ν = {[α′ν · q′ν · (μ = ν + 1 → k) ΣIIμ] − [αν · qν · (μ = ν → k) ΣIIμ]} − {[α ′ # ν · p ′ ν · (μ = ν + 1 → k) ΣIμ] − [α # ν · pν · (μ = ν → k) ΣIμ]} (7H)

In the case of tilt eccentricity, the case of taking Σ is considered as in the case of parallel eccentricity. When the decentered lens group is changed from the i-th surface to the j-th surface, for example, in Pε, (Pε) i to j = (ν = i → j) Σ {α′ν · q′ν · (μ = ν + 1 → k) ) ΣPμ−αν · qν · (μ = ν → k) ΣPμ] + [(α′ν / N′ν) − (αν / Nν)]} = α′j · q′j · (μ = j + 1 → k) ) ΣPμ−αi · qi · (μ = i → k) ΣPμ + (ν = i → j) Σ [(α′ν / N′ν) − (αν / Nν)] = (α′j · q′j− αi · qi) · (μ = j + 1 → k) ΣPμ−αi · qi · (μ = i → j) ΣPμ + [(α′j / N′j) − (αi / Ni)] = (α′j · q 'j-αi · qi) · (P) R-αi · qi · (P) D + [(α'j / N'j)-(αi / Ni)]
Where (P) R = (μ = j + 1 → k) ΣPμ: sum of aberration coefficients P of the image side group, (P) D = (μ = i → j) ΣPμ: sum of aberration coefficients P of the eccentric group is there. Therefore, Σ of the decentration aberration coefficient can be expressed by the sum of the aberration coefficients of the image side group, the sum of the aberration coefficients of the decentering group, and a constant term.

[Single-bokeh aberration]
The half-blurring aberration is expressed by equations (8A) and (8B) representing meridional one-sided blur (ΔM ″) i to j and sagittal one-sided blur (ΔS ″) i to j when performed in the same manner as in the case of parallel decentering. . Here, the amount of eccentricity is ε.
(ΔM ″) i˜j = −ε · FL · Y ′ · [3 · (IIIε) i to j + (Pε) i to j] (8A)
(ΔS ″) i˜j = −ε · FL · Y ′ · [(IIIε) i˜j + (Pε) i˜j] (8B)
However, the decentration aberration coefficient of the block is expressed for each of the meridional and sagittal by the following equations (8C) and (8D).
[3 · (IIIε) i˜j + (Pε) i˜j] = (α′j · q′j−αi · qi) · [3 · (III) R + (P) R] −αi · qi [3 · (III) D + (P) D] − (α ′ # j · p′j−α # i · pi) · [3 · (II) R] + α # i · pi [3 · (II) D] + [ (Α′j / N′j) − (αi / Ni)] (8C)
[(IIIε) i˜j + (Pε) i˜j] = (α′j · q′j−αi · qi) · [(III) R + (P) R] −αi · qi [(III) D + (P ) D] − (α ′ # j · p′j−α # i · pi) · [(II) R] + α # i · pi [(II) D] + [(α′j / N′j) − (Αi / Ni)] (8D)

[Axial coma]
If the axial coma is also performed in the same manner as in the case of parallel eccentricity, it will be expressed by equation (9A). However, the decentration aberration coefficient of the block is expressed by Expression (9B).
(AXCM ″) i˜j = ε · [(3 · κ ² · FL ³ ) / (8 · FNO ² )] · (IIE) i to j (9A)
(IIε) i˜j = (α′j · q′j−αi · qi) · (II) R−αi · qi · (II) D- (α ′ # j · p′j−α # i · pi ) · (I) R + α # i · pi · (I) D (9B)

  From the formulas (5E), (6E), (8A), and (9A), in the optical system with the same decentering amount, focal length, image height, and F number, the larger the decentering aberration coefficient, the more It can be seen that the aberration change is large. That is, in a lens group with a large decentration aberration coefficient of axial coma, the contrast decrease at the time of decentration is large, and in a lens group with a large decentration aberration coefficient of one-side blur aberration, the one-side blur at the time of decentration is large. I understand. In the present invention, the focus shift at the time of oblique projection is to be corrected by generating the one-sided blur aberration. However, due to the correction principle, it is desired to generate a certain amount of one-sided blur aberration due to decentering of the lens group. I want to keep the axial coma as small as possible. Therefore, as described in any one of claims 9 to 12, if the decentering aberration coefficient of the axial coma aberration is made smaller than the decentering aberration coefficient of the single blur aberration, the contrast at the time of focus correction The focus correction by the one-sided blur aberration can be performed without avoiding the decrease.

A projection lens according to a ninth aspect is characterized in that, in the invention according to any one of the first to eighth aspects, the projection lens satisfies the following conditional expression.
0.5 <| CMS1 / CAS1 | (4)
However,
CMS1 is a parallel decentration aberration coefficient related to the meridional image plane of the first lens group,
CMS1 = (α′j1−αi1) · [3 · (III) R1 + (P) R1] −αi1 · [3 · (III) D1 + (P) D1] − (α ′ # j1−α # i1) · [ 3 · (II) R1] + α # i1 · [3 · (II) D1].
α′j1: The converted inclination angle of the paraxial axial marginal ray on the final surface of the first lens group in the image space αi1: The converted inclination angle of the paraxial axial marginal ray on the starting surface of the first lens group in the object space (III) R1 : Sum of third-order aberration coefficient corresponding to astigmatism of second lens group and third lens group (P) R1: Third-order aberration corresponding to Petzval sum of second lens group and third lens group Sum of coefficients (III) D1: Sum of third-order aberration coefficients corresponding to astigmatism of the first lens group (P) D1: Sum of third-order aberration coefficients α ′ corresponding to Petzval sum of the first lens group # j1: The converted tilt angle in the image space of the paraxial off-axis chief ray on the final surface of the first lens group α # i1: The converted tilt angle in the object space of the paraxial off-axis chief ray on the starting surface of the first lens group (II) R1: Sum of third-order aberration coefficients corresponding to coma aberration of the second lens group and the third lens group (I I) D1: Sum of third-order aberration coefficients corresponding to coma in the first lens group
CAS1 is a parallel decentration aberration coefficient regarding the on-axis coma of the first lens group,
CAS1 = (α'j1-αi1) · (II) R1-αi1 · (II) D1- (α '# j1-α # i1) · (I) R1 + α # i1 · (I) D1
(I) R1: Sum of third-order aberration coefficients corresponding to spherical aberration of the second lens group and third lens group (I) D1: Sum of third-order aberration coefficients corresponding to spherical aberration of the first lens group

  According to the present invention, when the first lens group is shifted, one-sided blur can be generated while suppressing a decrease in contrast.

According to a tenth aspect of the present invention, in the invention according to any one of the first to ninth aspects, the projection lens satisfies the following conditional expression.
0.2 <| CMS2 / CAS2 | (5)
However,
CMS2 is a parallel decentration aberration coefficient related to the meridional image plane of the second lens group,
CMS2 = (α′j2−αi2) · [3 · (III) R2 + (P) R2] −αi2 · [3 · (III) D2 + (P) D2] − (α ′ # j2−α # i2) · [ 3 · (II) R2] + α # i2 · [3 · (II) D2].
α′j2: converted tilt angle in the image space of the paraxial axial marginal ray on the final surface of the second lens group αi2: converted tilt angle in the object space of the paraxial axial marginal ray on the starting surface of the second lens group (III) R2 : Sum of third-order aberration coefficient corresponding to astigmatism of third lens group (P) R2: Sum of third-order aberration coefficient corresponding to Petzval sum of third lens group (III) D2: Second lens Sum of third-order aberration coefficients corresponding to astigmatism of group (P) D2: Sum of third-order aberration coefficients corresponding to Petzval sum of second lens group α ′ # j2: Near at the final surface of second lens group Converted tilt angle α # i2 in the image space of the off-axis chief ray: Conversion tilt angle in the object space of the paraxial off-axis chief ray at the start surface of the second lens group (II) R2: Corresponding to the coma aberration of the third lens group Sum of third-order aberration coefficients (II) D2: third-order aberration relationship corresponding to coma aberration of the second lens group The sum of
CAS2 is a parallel decentration aberration coefficient related to the on-axis coma of the second lens group,
CAS2 = (α'j2-αi2) · (II) R2-αi2 · (II) D2- (α '# j2-α # i2) · (I) R2 + α # i2 · (I) D2
(I) R2: Sum of third-order aberration coefficients corresponding to spherical aberration of the third lens group (I) D2: Sum of third-order aberration coefficients corresponding to spherical aberration of the second lens group

  According to the present invention, when the second lens group is shifted, one-sided blur can be generated while suppressing a decrease in contrast.

The projection lens according to claim 11 is characterized in that, in the invention according to any one of claims 1 to 10, the projection lens satisfies the following conditional expression.
0.04 <| CMT1 / CAT1 | (6)
However,
CMT1 is a tilt decentration aberration coefficient related to the meridional image plane of the first lens group,
CMT1 = (α′j1 · q′j1−αi1 · qi1) · [3 · (III) R1 + (P) R1] −αi1 · qi1 [3 · (III) D1
+ (P) D1] − (α ′ # j1 · p′j1−α # i1 · pi1) · [3 · (II) R1] + α # i1 · pi1 [3 · (II) D1] + [(α ′ j1 / N′j1) − (αi1 / Ni1)].
q'j1: Distance from the rotation center when the first lens group is tilted to the reduction-side object plane of the first lens group
qi1: Distance from the rotation center when the first lens group is tilted to the magnification side image surface of the first lens group
p'j1: Distance between the rotation center when the first lens group is tilted and the exit pupil plane when light is incident on the first lens group from the magnification side
pi1: Distance between the rotation center when the first lens group is tilted and the entrance pupil plane when light is incident on the first lens group from the magnification side
N'j1: Refractive index of the reduction side space of the first lens unit
Ni1: Refractive index of the expansion side space of the first lens group
CAT1 is a tilt decentering aberration coefficient related to the on-axis coma of the first lens group,
CAT1 = (α′j1 · q′j1−αi1 · qi1) · (II) R1−αi1 · qi1 · (II) D1- (α ′ # j1 · p′j1−α # i1 · pi1) · (I) R1 + α # i1 · pi1 · (I) D1

  According to the present invention, when the first lens group is tilted, one-sided blur can be generated while suppressing a decrease in contrast.

According to a twelfth aspect of the present invention, in the invention according to any one of the first to eleventh aspects, the projection lens satisfies the following conditional expression.
5.0 <| CMT2 / CAT2 | (7)
However,
CMT2 is a tilt decentration aberration coefficient with respect to the meridional image plane of the second lens group,
CMT2 = (α'j2, q'j2-αi2, qi2), [3, (III) R2 + (P) R2] -αi2, qi2 [3, (III) D2
+ (P) D2]-(α '# j2 ・ p'j2-α # i2 ・ pi2) ・ [3 ・ (II) R2] + α # i2 ・ pi2 [3 ・ (II) D2] + [(α 'j2 / N'j2)-(αi2 / Ni2)].
q'j2: Distance from the rotation center when the second lens group is tilted to the reduction-side object plane of the second lens group
qi2: Distance from the center of rotation when the second lens group is tilted to the magnification side image surface of the second lens group
p'j2: Distance between the rotation center when the second lens group is tilted and the exit pupil plane when light is incident on the second lens group from the magnification side
pi2: Distance between the rotation center when the second lens group is tilted and the entrance pupil plane when light is incident on the second lens group from the magnification side
N'j2: Refractive index of the reduction side space of the second lens group
Ni2: Refractive index of the expansion side space of the second lens group
CAT2 is a tilt decentration aberration coefficient related to the on-axis coma of the second lens group,
CAT2 = (α'j2, q'j2-αi2, qi2), (II) R2-αi2, qi2, (II) D2- (α '# j2, p'j2-α # i2, pi2), (I) R2 + α # i2 · pi2 · (I) D2

  According to the present invention, when the second lens group is tilted, one-sided blur can be generated while suppressing a decrease in contrast.

  The various decentration aberration coefficients can be controlled in optical design. That is, as described in paragraphs [0078] and [0079] of the specification of Japanese Patent Application Laid-Open No. 11-30746, the third-order aberration coefficient dominant to the decentration aberration coefficient is the main factor that increases the decentration error sensitivity. Therefore, investigate which term of the decentration aberration coefficient is most affected by the decentration aberration coefficient of a specific group, and determine the most of the decentration aberration coefficient from the value of each term of the decentration aberration coefficient (or decentration aberration for each term) To identify specific terms. If the term can be specified, it is possible to specify which third-order aberration coefficient is dominant, and it is sufficient to design to reduce the third-order aberration coefficient specified here.

  An imaging lens according to a thirteenth aspect is characterized in that in the invention according to any one of the first to twelfth aspects, the imaging lens further includes a lens having substantially no power. That is, even when a dummy lens having substantially no power is added to the configuration of claim 1, it is within the scope of application of the present invention.

  A projection apparatus according to a fourteenth aspect is the projection lens according to any one of the first to thirteenth aspects, a detection unit that detects an inclination angle of the optical axis of the projection apparatus with respect to a screen, and the first unit according to the inclination angle. And changing means for changing the relative decentering amount of the first lens group and the second lens group.

  According to the present invention, even if the optical axis of the projection apparatus is installed at an arbitrary angle with respect to the screen, it is possible to correct the focus accordingly.

  According to the present invention, when an image is projected obliquely in a projection device, focus correction is realized by generating one-sided blur due to the eccentricity of the lens group of the optical system. A projection lens and a projection apparatus can be provided.

It is a figure for demonstrating the relationship between an optical system and a coordinate, and an aberration coefficient. It is a figure for demonstrating derivation | leading-out of a decentration aberration coefficient. It is a perspective view of the imaging device concerning this embodiment. It is sectional drawing of the projection lens of Example 1 in object distance 500mm. FIG. 4A is a spherical aberration diagram (a), an astigmatism diagram (b), and a distortion aberration diagram (c) of Example 1 at an object distance of 1020 mm. FIG. 5A is a spherical aberration diagram of the first example at an object distance of 500 mm, FIG. 6B is an astigmatism diagram, and FIG. FIG. 5A is a spherical aberration diagram of the first example at the object distance of 160 mm, FIG. 6B is an astigmatism diagram, and FIG. It is sectional drawing of the projection lens of Example 2 in object distance 500mm. FIG. 6 is a spherical aberration diagram (a), an astigmatism diagram (b), and a distortion aberration diagram (c) of Example 2 at an object distance of 1020 mm. FIG. 5A is a spherical aberration diagram (a), an astigmatism diagram (b), and a distortion aberration diagram (c) of Example 2 at an object distance of 500 mm. FIG. 6A is a spherical aberration diagram of the second example at the object distance of 160 mm, FIG. 6B is an astigmatism diagram, and FIG. It is sectional drawing of the projection lens of Example 3 in object distance 500mm. FIG. 6A is a spherical aberration diagram (a), an astigmatism diagram (b), and a distortion aberration diagram (c) of Example 3 at an object distance of 1020 mm. FIG. 6A is a spherical aberration diagram of the third embodiment at an object distance of 500 mm, FIG. 6B is an astigmatism diagram, and FIG. FIG. 7A is a spherical aberration diagram of the third example at an object distance of 160 mm, FIG. 6B is an astigmatism diagram, and FIG. It is sectional drawing of the projection lens of Example 4 in object distance 500mm. FIG. 6A is a spherical aberration diagram (a), an astigmatism diagram (b), and a distortion aberration diagram (c) of Example 4 at an object distance of 1020 mm. FIG. 6A is a spherical aberration diagram of the fourth embodiment at an object distance of 500 mm, FIG. 6B is an astigmatism diagram, and FIG. FIG. 10A is a spherical aberration diagram of the fourth example at the object distance of 160 mm, FIG. 6B is an astigmatism diagram, and FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing the projection apparatus PJ according to the present embodiment. The projection apparatus PJ is a light valve LB composed of a projection lens PL, a wire grid WG as a polarization separation element, and a reflective display element such as a digital micromirror device or LCOS (liquid crystal on silicon). And an illumination lens IL, a light source OS, a lens driving device DR, a control device CONT, and detection means TS for detecting an inclination angle of the optical axis X of the projection device PJ with respect to the normal line of the screen SC. The detection means TS may be a level or the like. The lens driving device DR and the control device CONT constitute changing means.

  The projection lens PL includes, in order from the enlargement side (screen side), a negative first lens group G1, a positive second lens group G2, and a positive third lens group G3, and includes a first lens group G1, a second lens group G2, and a second lens group G2. Each of the lens groups G2 preferably has at least one positive lens and one negative lens.

  More preferably, the first lens group G1 includes, in order from the magnification side, a first lens having a negative refractive power, a second lens having a positive refractive power, and a third lens having a negative refractive power. The lens group G2 includes a fourth lens having a negative refractive power, a fifth lens having a positive refractive power, and a sixth lens having a positive refractive power, and is disposed between the first lens group G1 and the second lens group G2. An aperture stop is provided, and the third lens group G3 is composed of one positive lens. At this time, it is preferable that the second lens and the third lens are cemented with each other. In addition, it is preferable that the fourth lens and the fifth lens are cemented with each other.

  The operation of the projection device PJ will be described. The light emitted from the light source OS passes through the illumination lens IL, becomes a parallel light beam, is reflected by the wire grid WG, passes through the third lens group G3, and enters the light valve LB. The light valve LB modulates and reflects the incident light based on image data or the like. The modulated light again passes through the third lens group G3 and the wire grid WG, is enlarged through the second lens group G2 and the first lens group G1, and projects an image on the screen SC. .

  Here, when the detection means TS detects the inclination of the projection device PJ, a signal corresponding to the detection device TS is output to the control device CONT. The control device CONT determines a lens shift amount so that the image blur is appropriately corrected according to the inclination of the projection device PJ, and the first lens group G1 and the second lens group via the lens driving device DR. Are relatively shifted (eccentric) in the direction perpendicular to the optical axis. Thereby, even when the projection device PJ is tilted, blurring of an image projected on the screen SC can be suppressed. In the present embodiment, both the first lens group G1 and the second lens group G2 are relatively decentered to perform focus correction. However, only the first lens group G1 is decentered and only the second lens group G2 is decentered. Focus correction by eccentricity of

(Example)
Next, examples suitable for the above-described embodiment will be described. However, the present invention is not limited to the following examples. Symbols used in each example are as follows.
f: Focal length of the entire system (mm)
R: radius of curvature (mm)
d: Shaft upper surface distance (mm)
nd: refractive index with respect to d-line νd: Abbe number

  In each embodiment, the surface described with “*” after each surface number is a surface having an aspheric shape, and the shape of the aspheric surface has the vertex of the surface as the origin and the X axis in the optical axis direction. The height in the direction perpendicular to the optical axis is h and is expressed by the following “Equation 2”.

However,
Ai: i-order aspheric coefficient R: radius of curvature K: conic constant

Example 1
Lens data is shown in Table 1. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed using E (for example, 2.5E-02). FIG. 4 is a sectional view of the projection lens of Example 1 at an object distance of 500 mm. In the figure, G1 is a first lens L1 having a negative refractive power, a second lens L2 having a positive refractive power, and a third lens L3 having a negative refractive power in order from the magnification side (L2 and L3 are cemented lenses). G2 is a fourth lens L4 having negative refracting power, a fifth lens L5 having positive refracting power (L4 and L5 are cemented lenses), positive refracting in order from the enlargement side. G3 is a third lens group including only a seventh lens L7 having a positive refractive power. An aperture stop S is provided between the first lens group G1 and the second lens group G2. CG is a cover glass, and LB is a light valve.

  FIG. 5 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 1 at an object distance of 1020 mm. FIG. 6 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 1 at an object distance of 500 mm. FIG. 7 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 1 at an object distance of 160 mm. Here, in the spherical aberration diagram, g represents the amount of spherical aberration with respect to the g line, and d represents the amount of spherical aberration with respect to the d line. In the graph showing astigmatism, a solid line ΔS represents a sagittal plane, and a dotted line ΔM represents a meridional plane (the same applies hereinafter).

(Table 1)
Example 1

Surface number (aspherical surface) R (mm) d (mm) nd νd
1 9.197 0.50 1.63626 58.5
2 3.333 1.30
3 7.553 1.50 1.84666 24.0
4 -26.199 0.60 1.48749 70.2
5 3.580 1.50
6 (Aperture) ∞ 1.00
7 -7.008 0.50 1.63200 23.0
8 5.946 1.95 1.72916 54.7
9 -4.724 0.50
10 * 4.536 1.50 1.49 140 59.9
11 * 29.720 d (variable)
12 * 5.897 1.46 1.49 140 59.9
13 * -15.526 1.10
14 ∞ 0.70 1.51680 64.2
15 ∞

Aspheric coefficient 10th surface
K = 0
A4 = -3.16996E-04
A6 = -5.66583E-05
A8 = 1.20989E-05
A10 = -1.56971E-06

11th page
K = 0
A4 = 4.78675E-04
A6 = -1.78229E-05
A8 = 6.19464E-06
A10 = -1.35783E-06

12th page
K = 0
A4 = -6.38238E-03
A6 = 2.05265E-03
A8 = -5.08031E-04
A10 = 2.84688E-05

Side 13
K = 0
A4 = 3.38826E-03
A6 = 1.48815E-03
A8 = -3.81096E-04
A10 = 8.64102E-07
A12 = 2.74701E-06

1st lens object side-object distance (mm) 1020 500 160
Focal length (mm) 3.60 3.61 3.64
F number 1.33 1.33 1.34
Half angle of view (°) 34.3 34.2 34.0
Image height (mm) 2.40 2.40 2.40
Total lens length (mm) 18.13 18.16 18.25
Back focus 1.56 1.56 1.56
d (variable) (mm) 4.020 4.043 4.136

  In this embodiment, focusing is performed by moving the first lens group G1 and the second lens group G2 together on the optical axis. In the present embodiment, it is assumed that the wire grid is inserted with an inclination of 45 degrees with respect to the optical axis between the sixth lens L6 and the seventh lens L7. As a result, the illumination light is incident vertically from the optical axis, reflected by the wire grid in the direction of the light valve LB, illuminates the light valve LB, and this time, the light beam reflected by the reflective light valve LB becomes projection light. Head to the screen side. However, the illumination light may be incident from the back side of the light valve using the transmission type light valve LB without using the wire grid (or the polarization beam splitter).

(Example 2)
Lens data is shown in Table 1. FIG. 8 is a sectional view of the projection lens of Example 2 at an object distance of 500 mm. In the figure, G1 is a first lens L1 having a negative refractive power, a second lens L2 having a positive refractive power, and a third lens L3 having a negative refractive power in order from the magnification side (L2 and L3 are cemented lenses). G2 is a fourth lens L4 having negative refracting power, a fifth lens L5 having positive refracting power (L4 and L5 are cemented lenses), positive refracting in order from the enlargement side. G3 is a third lens group including only a seventh lens L7 having a positive refractive power. An aperture stop S is provided between the first lens group G1 and the second lens group G2. CG is a cover glass, and LB is a light valve.

  FIG. 9 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 2 at an object distance of 1020 mm. FIG. 10 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 2 at an object distance of 500 mm. FIG. 11 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 2 at an object distance of 160 mm.

(Table 2)
Example 2

Surface number (aspherical surface) R (mm) d (mm) nd νd
1 15.154 0.40 1.72916 54.7
2 2.987 1.03
3 6.868 1.02 1.92286 20.9
4 -43.779 0.50 1.48749 70.2
5 * 2.839 2.59
6 (Aperture) ∞ 0.50
7 -19.294 0.40 1.92286 20.9
8 6.010 1.29 1.88300 40.8
9 -11.323 0.20
10 * 13.423 1.38 1.72916 54.7
11 * -5.652 d (variable)
12 * 4.832 1.00 1.72916 54.7
13 * 267.288 0.70
14 ∞ 0.70 1.51680 64.2
15 ∞

Aspheric coefficient Fifth surface
K = 0
A4 = -2.42461E-03
A6 = 1.47929E-04
A8 = -1.45728E-04
A10 = -6.41158E-06

10th page
K = 0
A4 = -9.59673E-05
A6 = 1.89607E-05
A8 = -5.90206E-06
A10 = 2.60797E-06

11th page
K = 0
A4 = 9.85420E-04
A6 = 5.02904E-05
A8 = -1.98530E-05
A10 = 3.88919E-06

12th page
K = 0
A4 = 5.38523E-03
A6 = -1.23116E-03

Side 13
K = 0
A4 = 1.87828E-02
A6 = -3.70456E-03
A8 = 2.21292E-04

1st lens object side-object distance (mm) 1020 500 160
Focal length (mm) 2.89 2.90 2.92
F number 1.46 1.47 1.48
Half angle of view (°) 39.7 39.7 39.6
Image height (mm) 2.29 2.30 2.31
Total lens length (mm) 18.31 18.33 18.39
Back focus (mm) 1.19 1.19 1.19
d (variable) (mm) 6.570 6.585 6.649

  In this embodiment, focusing is performed by moving the first lens group G1 and the second lens group G2 together on the optical axis. In the present embodiment, it is assumed that the wire grid is inserted with an inclination of 45 degrees with respect to the optical axis between the sixth lens L6 and the seventh lens L7. As a result, the illumination light is incident vertically from the optical axis, reflected by the wire grid in the direction of the light valve LB, illuminates the light valve LB, and this time, the light beam reflected by the reflective light valve LB becomes projection light. Head to the screen side. However, the illumination light may be incident from the back side of the light valve using the transmission type light valve LB without using the wire grid or the polarization beam splitter.

(Example 3)
Table 3 shows lens data. FIG. 12 is a cross-sectional view of the projection lens of Example 3 at an object distance of 500 mm. In the figure, G1 is a first lens L1 having a negative refractive power, a second lens L2 having a positive refractive power, and a third lens L3 having a negative refractive power in order from the magnification side (L2 and L3 are cemented lenses). G2 is a fourth lens L4 having negative refracting power, a fifth lens L5 having positive refracting power (L4 and L5 are cemented lenses), positive refracting in order from the enlargement side. G3 is a third lens group including only a seventh lens L7 having a positive refractive power. An aperture stop S is provided between the first lens group G1 and the second lens group G2. CG is a cover glass, and LB is a light valve.

  FIG. 13 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 3 at an object distance of 1020 mm. FIG. 14 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 3 at an object distance of 500 mm. FIG. 15 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 3 at an object distance of 160 mm.

(Table 3)
Example 3

Surface number (aspherical surface) R (mm) d (mm) nd νd
1 1476.353 0.40 1.72916 54.7
2 2.877 0.88
3 7.797 1.33 1.92286 20.9
4 -8.506 0.40 1.48749 70.2
5 * 4.799 1.44
6 (Aperture) ∞ 0.42
7 -7.902 0.50 1.92286 20.9
8 4.985 1.85 1.88300 40.8
9 -7.196 0.20
10 * 16.461 1.50 1.72916 54.7
11 * -6.130 d (variable)
12 * 5.558 1.00 1.72916 54.7
13 * 40.031 0.70
14 ∞ 0.70 1.51680 64.2
15 ∞

Aspheric coefficient Fifth surface
K = 0
A4 = -7.66064E-05
A6 = 1.84545E-04
A8 = -1.47297E-04
A10 = 3.98153E-06

10th page
K = 0
A4 = -5.09234E-04
A6 = -5.76204E-05
A8 = 8.79418E-06
A10 = -1.72176E-06

11th page
K = 0
A4 = 2.18754E-04
A6 = -8.41402E-05
A8 = 1.40068E-05
A10 = -1.79911E-06

12th page
K = 0
A4 = 1.93527E-03
A6 = -2.98705E-04

Side 13
K = 0
A4 = 7.70509E-03
A6 = -1.14136E-03
A8 = 7.12592E-05

1st lens object side-object distance (mm) 1020 500 160
Focal length (mm) 3.47 3.47 3.50
F number 1.69 1.69 1.70
Half angle of view (°) 34.7 34.7 34.6
Image height (mm) 2.16 2.16 2.16
Total lens length (mm) 18.53 18.55 18.63
Back focus (mm) 1.18 1.18 1.18
d (variable) (mm) 7.197 7.216 7.297

  In this embodiment, focusing is performed by moving the first lens group G1 and the second lens group G2 together on the optical axis. In the present embodiment, it is assumed that the wire grid is inserted with an inclination of 45 degrees with respect to the optical axis between the sixth lens L6 and the seventh lens L7. As a result, the illumination light is incident vertically from the optical axis, reflected by the wire grid in the direction of the light valve LB, illuminates the light valve LB, and this time, the light beam reflected by the reflective light valve LB becomes projection light. Head to the screen side. However, the illumination light may be incident from the back side of the light valve using the transmission type light valve LB without using the wire grid or the polarization beam splitter.

Example 4
Table 4 shows the lens data. FIG. 16 is a sectional view of the projection lens of Example 4 at an object distance of 500 mm. In the figure, G1 is a first lens L1 having a negative refractive power, a second lens L2 having a positive refractive power, and a third lens L3 having a negative refractive power in order from the magnification side (L2 and L3 are cemented lenses). G2 is a fourth lens L4 having negative refracting power, a fifth lens L5 having positive refracting power (L4 and L5 are cemented lenses), positive refracting in order from the enlargement side. G3 is a third lens group including only a seventh lens L7 having a positive refractive power. An aperture stop S is provided between the first lens group G1 and the second lens group G2. CG is a cover glass, and LB is a light valve.

  FIG. 15 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 4 at an object distance of 1020 mm. FIG. 16 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 4 at an object distance of 500 mm. FIG. 17 is a spherical aberration diagram (a), astigmatism diagram (b), and distortion diagram (c) of Example 4 at an object distance of 160 mm.

(Table 4)
Example 4

Surface number (aspherical surface) R (mm) d (mm) nd νd
1 -16.269 0.40 1.72916 54.7
2 2.960 1.23
3 31.159 1.26 1.92286 20.9
4 -5.832 0.40 1.49710 81.6
5 * -93.457 d1 (variable)
6 (Aperture) ∞ 0.41
7 -10.162 0.40 1.92286 20.9
8 5.792 1.96 1.80420 46.5
9 -5.880 0.20
10 * 11.088 1.08 1.80139 45.4
11 * -22.475 d2 (variable)
12 * 5.070 1.00 1.72903 54.0
13 * 77.844 0.70
14 ∞ 0.70 1.51680 64.2
15 ∞

Aspheric coefficient Fifth surface
K = 0
A4 = -2.22777E-03
A6 = -1.43779E-04
A8 = -2.74206E-05
A10 = -1.55305E-06

10th page
K = 0
A4 = -6.64175E-04
A6 = -2.08289E-04
A8 = 1.97456E-05
A10 = -3.90539E-06

11th page
K = 0
A4 = -7.70784E-04
A6 = -1.96056E-04
A8 = 1.20762E-05
A10 = -2.59126E-06

12th page
K = 0
A4 = 1.38370E-03
A6 = 1.92668E-04
A8 = -1.30428E-04
A10 = 2.20810E-06

Side 13
K = 0
A4 = 9.66722E-03
A6 = -1.70381E-04
A8 = -2.82686E-04
A10 = 2.14306E-05

Distance between first lens object side surface and object (mm) 1020 500 160
Focal length (mm) 3.34 3.36 3.43
F number 1.68 1.69 1.71
Half angle of view (°) 35.7 35.6 35.1
Image height (mm) 2.18 2.18 2.20
Total lens length (mm) 19.62 19.62 19.62
Back focus (mm) 1.19 1.19 1.19
d1 (variable) (mm) 2.163 2.133 2.000
d2 (variable) (mm) 7.698 7.728 7.862

  In this embodiment, focusing is performed by moving only the second lens group G2 on the optical axis. In the present embodiment, it is assumed that the wire grid is inserted with an inclination of 45 degrees with respect to the optical axis between the sixth lens L6 and the seventh lens L7. As a result, the illumination light is incident vertically from the optical axis, reflected by the wire grid in the direction of the light valve LB, illuminates the light valve LB, and this time, the light beam reflected by the reflective light valve LB becomes projection light. Head to the screen side. However, the illumination light may be incident from the back side of the light valve using the transmission type light valve LB without using the wire grid or the polarization beam splitter.

(MTF calculation result during oblique projection and focus correction)
For each example, the performance change of the optical system at the time of oblique projection and when the focus was corrected by decentering the lens group was evaluated by MTF. Here, for the convenience of simulation, the MTF calculation is performed not on the screen side (enlargement side) but on the light valve side (reduction side). That is, the screen is the object point and the light valve is the image point. Note that the focus position change on the enlargement side can be expressed as (focus change amount on the reduction side) / ((horizontal magnification) ^ 2).

  The optical system rotation reference at the time of oblique projection is the center of the light valve (reduction side), and at the same time, the screen center defocus that occurs at this time is corrected by moving the light valve in the optical axis direction. The focus deviation on the center of the screen is corrected with the focus group on the actual machine, but this correction changes the aberration balance and makes it difficult to grasp the effect of the net oblique projection. The focus is adjusted again.

  The wavelength weight of MTF is C line (656.27 nm): e line (546.07 nm): F line (486.13 nm) = 1: 1: 1, and the spatial frequency is 100 lines / mm. The one-sided blur amount represents a difference in peak position between the plus image height and the minus image height. For example, in Example 1, the amount of one-side blur at an image height of 1.125 mm during oblique projection is | 8.5−2.9 | = 5.6 μm. Of course, in an optical system in which no eccentricity occurs, the amount of one-sided blur is zero.

  The MTF absolute value is the value at the screen center focus position, and the peak position is the value when the screen center focus position is set to zero. In this embodiment, the simulation is performed by decentering only the first lens group or the second lens group. However, the first lens group and the second lens group may be decentered simultaneously. The examination result of each Example is shown to Tables 5-8.

  Table 9 shows the numerical values of the respective examples corresponding to the formulas in the claims.

  From the above results, it was confirmed that by taking the focus correction means according to the present invention, the amount of one-sided blur generated during oblique projection can be reduced, and the amount of change in MTF can also be reduced to a small extent.

CONT control device G1 to G3 lens group IL illumination lens L1 to L7 lens LB light valve DR lens driving device OS light source PJ projection device PL projection lens SC screen TS detection means WG wire grid

Claims (14)

  A projection lens for a projection apparatus that magnifies and projects an image onto a screen, which is composed of a negative first lens group, a positive second lens group, and a positive third lens group in order from the magnification side. The focus deviation on the screen that occurs when projecting so that the optical axis is inclined with respect to the lens is corrected by relatively decentering the first lens group and the second lens group, Projection lens.   2. The projection lens according to claim 1, wherein each of the first lens group and the second lens group includes at least one positive lens and one negative lens.   The first lens group includes, in order from the magnification side, a first lens having a negative refractive power, a second lens having a positive refractive power, and a third lens having a negative refractive power, and the second lens group includes It consists of a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power, and an aperture stop is provided between the first lens group and the second lens group 3. The projection lens according to claim 1, wherein the third lens group includes a single positive lens.   4. The projection lens according to claim 3, wherein the second lens and the third lens are cemented with each other.   5. The projection lens according to claim 3, wherein the fourth lens and the fifth lens are cemented with each other. 6. The projection lens according to claim 1, wherein the first lens group satisfies the following conditional expression.
-3.0 <f1 / f <-1.0 (1)
However,
f1: Composite focal length of the first lens group
f: Focal length of the entire projection lens system 7. The projection lens according to claim 1, wherein the second lens group satisfies the following conditional expression.
1.0 <f2 / f <2.0 (2)
However,
f2: Composite focal length of the second lens group
f: Focal length of the entire projection lens system 8. The projection lens according to claim 1, wherein the first lens group and the second lens group satisfy the following conditional expression.
-2.0 <f1 / f2 <-0.5 (3)
However,
f1: Composite focal length of the first lens group f2: Composite focal length of the second lens group 9. The projection lens according to claim 1, wherein the projection lens satisfies the following conditional expression.
0.5 <| CMS1 / CAS1 | (4)
However,
CMS1 is a parallel decentration aberration coefficient related to the meridional image plane of the first lens group,
CMS1 = (α'j1-αi1) ・ [3 ・ (III) R1 + (P) R1] -αi1 ・ [3 ・ (III) D1 + (P) D1]-(α '# j1-α # i1) ・ [ 3 · (II) R1] + α # i1 · [3 · (II) D1].
α′j1: Conversion tilt angle in the image space of the paraxial axial marginal ray on the final surface of the first lens group αi1: Conversion tilt angle in the object space of the paraxial axial marginal ray on the first lens group starting surface
(III) R1: Sum of third-order aberration coefficients corresponding to astigmatism of the second lens group and the third lens group
(P) R1: Sum of third-order aberration coefficients corresponding to Petzval sum of the second lens group and the third lens group
(III) D1: Sum of third-order aberration coefficients corresponding to astigmatism of the first lens group
(P) D1: Sum of third-order aberration coefficients corresponding to the Petzval sum of the first lens group α ′ # j1: Equivalent inclination α # i1 in the image space of the paraxial off-axis principal ray on the final surface of the first lens group : Paraxial off-axis principal ray at the starting surface of the first lens group, converted inclination angle in object space
(II) R1: Sum of third-order aberration coefficients corresponding to coma aberration of the second lens group and the third lens group
(II) D1: Sum of third-order aberration coefficients corresponding to coma in the first lens group
CAS1 is a parallel decentration aberration coefficient regarding the on-axis coma of the first lens group,
CAS1 = (α'j1-αi1) · (II) R1-αi1 · (II) D1- (α '# j1-α # i1) · (I) R1 + α # i1 · (I) D1
(I) R1: Sum of third-order aberration coefficients corresponding to spherical aberration of the second lens group and the third lens group
(I) D1: Sum of third-order aberration coefficients corresponding to the spherical aberration of the first lens group 10. The projection lens according to claim 1, wherein the projection lens satisfies the following conditional expression.
0.2 <| CMS2 / CAS2 | (5)
However,
CMS2 is a parallel decentration aberration coefficient related to the meridional image plane of the second lens group,
CMS2 = (α'j2-αi2) ・ [3 ・ (III) R2 + (P) R2] -αi2 ・ [3 ・ (III) D2 + (P) D2]-(α '# j2-α # i2) ・ [ 3 · (II) R2] + α # i2 · [3 · (II) D2].
α′j2: converted inclination angle of the paraxial axial marginal ray on the final surface of the second lens group in the image space αi2: converted inclination angle of the paraxial axial marginal ray on the starting surface of the second lens group in the object space
(III) R2: Sum of third-order aberration coefficients corresponding to astigmatism of the third lens group
(P) R2: Sum of third-order aberration coefficients corresponding to Petzval sum of the third lens group
(III) D2: Sum of third-order aberration coefficients corresponding to astigmatism of the second lens group
(P) D2: sum of third-order aberration coefficients corresponding to Petzval sum of the second lens group α ′ # j2: converted inclination angle α # i2 in the image space of the paraxial off-axis principal ray on the final surface of the second lens group : Paraxial off-axis principal ray on the starting surface of the second lens group, converted inclination angle in object space
(II) R2: Sum of third-order aberration coefficients corresponding to coma in the third lens group
(II) D2: Sum of third-order aberration coefficients corresponding to coma in the second lens group
CAS2 is a parallel decentration aberration coefficient related to the on-axis coma of the second lens group,
CAS2 = (α'j2-αi2) · (II) R2-αi2 · (II) D2- (α '# j2-α # i2) · (I) R2 + α # i2 · (I) D2
(I) R2: Sum of third-order aberration coefficients corresponding to the spherical aberration of the third lens group
(I) D2: Sum of third-order aberration coefficients corresponding to the spherical aberration of the second lens group 11. The projection lens according to claim 1, wherein the projection lens satisfies the following conditional expression.
0.04 <| CMT1 / CAT1 | (6)
However,
CMT1 is a tilt decentration aberration coefficient related to the meridional image plane of the first lens group,
CMT1 = (α'j1 ・ q'j1-αi1 ・ qi1) ・ [3 ・ (III) R1 + (P) R1] -αi1 ・ qi1 [3 ・ (III) D1
+ (P) D1]-(α '# j1 ・ p'j1-α # i1 ・ pi1) ・ [3 ・ (II) R1] + α # i1 ・ pi1 [3 ・ (II) D1] + [(α 'j1 / N'j1)-(αi1 / Ni1)].
q'j1: Distance from the rotation center when the first lens group is tilted to the reduction-side object plane of the first lens group
qi1: Distance from the rotation center when the first lens group is tilted to the magnification side image surface of the first lens group
p'j1: Distance between the rotation center when the first lens group is tilted and the exit pupil plane when light is incident on the first lens group from the magnification side
pi1: Distance between the rotation center when the first lens group is tilted and the entrance pupil plane when light is incident on the first lens group from the magnification side
N'j1: Refractive index of the reduction side space of the first lens unit
Ni1: Refractive index of the expansion side space of the first lens group
CAT1 is a tilt decentering aberration coefficient related to the on-axis coma of the first lens group,
CAT1 = (α'j1, q'j1-αi1, qi1), (II) R1-αi1, qi1, (II) D1- (α '# j1, p'j1-α # i1, pi1), (I) R1 + α # i1 · pi1 · (I) D1 12. The projection lens according to claim 1, wherein the projection lens satisfies the following conditional expression.
5.0 <| CMT2 / CAT2 | (7)
However,
CMT2 is a tilt decentration aberration coefficient with respect to the meridional image plane of the second lens group,
CMT2 = (α'j2, q'j2-αi2, qi2), [3, (III) R2 + (P) R2] -αi2, qi2 [3, (III) D2
+ (P) D2]-(α '# j2 ・ p'j2-α # i2 ・ pi2) ・ [3 ・ (II) R2] + α # i2 ・ pi2 [3 ・ (II) D2] + [(α 'j2 / N'j2)-(αi2 / Ni2)]
q'j2: Distance from the rotation center when the second lens group is tilted to the reduction-side object plane of the second lens group
qi2: Distance from the center of rotation when the second lens group is tilted to the magnification side image surface of the second lens group
p'j2: Distance between the rotation center when the second lens group is tilted and the exit pupil plane when light is incident on the second lens group from the magnification side
pi2: Distance between the rotation center when the second lens group is tilted and the entrance pupil plane when light is incident on the second lens group from the magnification side
N'j2: Refractive index of the reduction side space of the second lens group
Ni2: Refractive index of the expansion side space of the second lens group
CAT2 is a tilt decentration aberration coefficient related to the on-axis coma of the second lens group,
CAT2 = (α'j2, q'j2-αi2, qi2), (II) R2-αi2, qi2, (II) D2- (α '# j2, p'j2-α # i2, pi2), (I) R2 + α # i2 · pi2 · (I) D2   The imaging lens according to claim 1, further comprising a lens having substantially no power.   The projection lens according to any one of claims 1 to 13, detection means for detecting an inclination angle of the optical axis of the projection apparatus with respect to the screen, and the first lens group and the second lens group according to the inclination angle. A projection device comprising: a changing unit that changes a relative eccentricity amount.