JP2006243019A - Projection lens and projection type picture display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection lens which realizes such a wide viewing angle that a half viewing angle is ≥40°, which has a long back focus and high telecentricity on a reduction side, and whose lateral chromatic aberration is corrected to be reduced sufficiently. <P>SOLUTION: The projection lens is constituted by arranging a 1st negative lens group I, an aperture stop ST, and a 2nd positive lens group II in order from an enlargement side, and is telecentric on the reduction side. The 2nd lens group II is constituted of: a doublet comprising a 1st negative lens having a large curvature on the reduction side and a 1st positive lens having a large curvature on the enlargement side; and a 2nd positive lens having a large curvature on the enlargement side; and further one or two negative lenses having small Abbe number arranged singly or as a doublet constituted with a positive lens having larger Abbe number nearer to the reduction side than the 2nd positive lens in order from the enlargement side. The refractive index of the 1st negative lens: N<SB>1</SB>, the refractive index of the 1st positive lens: N<SB>2</SB>and the Abbe number of the 2nd positive lens: ν<SB>II3</SB>satisfy conditions: (1) 0.13<N<SB>1</SB>-N<SB>2</SB><0.20, (2) 15<ν<SB>II3</SB><30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a projection lens and a projection type image display device.

  "Rear projector" that displays each color image of red, green, and blue individually on three panels (liquid crystal light valve, etc.), and synthesizes each color image and displays it at a wide angle of view from the back of the transmissive screen. Since the apparatus is thin and the display image on the large screen is high definition, it is widely used as a general TV broadcast, video playback image, and computer display device. Among them, those using a reflective panel are expected to become more popular because of their structure, because pixels can be made smaller and more precise than those using a transmissive panel.

  "Rear projectors that use reflective panels" generally separate light from a white light source into red, green, and blue colors using a color separation optical system, guide each reflected panel, and reflect the reflected light from each reflective panel Light (two-dimensionally modulated by images displayed on each panel) is combined by a color combining optical system and is incident on a projection lens.

  For this reason, a PBS (polarizing beam splitter) that guides each color of red, green, and blue to the reflection type panel and “an optical component such as a prism as a color synthesis optical system” are arranged between the projection lens and the reflection type panel. Therefore, a “long back focus” is required for the projection lens.

  In addition, when the angle of light incident on the color synthesis optical system from the reflective panel changes, the spectral transmittance of the color synthesis optical system changes accordingly, so the brightness of each color in the projected color image depends on the angle of view. Since the image changes and becomes difficult to see, it is preferable that the projection lens has “a telecentric property that the angle of the principal ray is substantially parallel to the optical axis on the reduction side”.

  As a “projection lens having a long back focus and a telecentric reduction side”, a so-called “lens group having a negative refractive power” and a “lens group having a positive refractive power” are arranged in order from the enlargement side. "Retro focus type" is known (Patent Documents 1 to 4).

  In this type of projection lens, the refractive power distribution on the enlargement side and the reduction side is asymmetric with respect to the aperture stop, so that distortion and lateral chromatic aberration are likely to occur.

JP2003-5069 JP 2003-195164 A JP 2004-354405 A JP 2005-004074 A

  The present invention is a retrofocus type projection that can achieve a wide angle of view of 40 degrees or more, has a long back focus and "high telecentricity on the reduction side", and is corrected with sufficiently small chromatic aberration of magnification. The realization of a lens for use is an issue. Another object of the present invention is to realize a projection-type image display device that can display a high-definition projection image by using this projection lens.

  As shown in FIG. 1, the projection lens of the present invention includes a first lens group I having a negative refractive power from the enlargement side (left side in the figure) to the reduction side (right side in the figure), an aperture stop. ST is a retrofocus type in which the second lens group II having positive refractive power is arranged in the above order, and is telecentric on the reduction side. The symbol P in FIG. 1 indicates “the PBS that guides each color of red, green, and blue to the reflective panel and the prism that is the color synthesis optical system”, and the symbol RP indicates each image of red, green, and blue. A reflection type panel to be displayed is shown in a simplified form.

  In the second lens group II, “three lenses on the enlargement side” are composed of a negative lens (first negative lens), a positive lens (first positive lens), and a positive lens (second positive lens). The negative lens has “a large curvature on the reduction side”. The first positive lens has “a large curvature on the enlargement side” and is bonded to the reduction side of the first negative lens. That is, the most magnified side of the second lens group is “a cemented lens of the first negative lens and the first positive lens”. The second positive lens following the first positive lens has “a large curvature on the enlargement side”.

  That is, the second lens group starts from the above-mentioned “configuration including the first negative lens, the first positive lens, and the second positive lens” from the enlargement side to the reduction side.

  One or two negative lenses having a small Abbe number are arranged on the reduction side of the second lens group with respect to the second positive lens. These one or two “negative lenses having a small Abbe number” are arranged alone or as “a cemented lens bonded to a positive lens having a larger Abbe number”. These “one or two negative lenses having a small Abbe number” are used for correcting lateral chromatic aberration. The Abbe number of these negative lenses having a small Abbe number is preferably 45 or less.

The refractive index of the first negative lens: N ₁ , the refractive index of the first positive lens: N ₂ , and the Abbe number of the second positive lens: ν _II3 are the conditions:
_{(1) 0.13 <N 1 -N} 2 <0.20
(2) 15 < _νII3 <30
Satisfied.

In the projection lens according to claim 1, the partial dispersion ratio: θ _gF and the Abbe number: ν _II3 of the second positive lens in the second lens group are:
_{(3) 0 <θ gF -} (0.6438-0.001682ν II3) <0.04
Is preferably satisfied (claim 2).
3. The projection lens according to claim 1, wherein the back focus in the air when the conjugate point on the enlargement side is infinity: Bf, the focal length of the entire system: f, and the focal length of the first lens group: f1. conditions:
(4) 4.0 <Bf / f <6.8
(5) 2.4 <| f1 / f | <3.0
Is preferably satisfied (Claim 3).

The projection lens according to any one of claims 1 to 3, wherein the second lens group includes "one plastic lens having negative refractive power", and the focal length of the plastic lens: f _P , second The focal length of the lens group: f2 is a condition:
(6) 2.5 <| f _P /f2|<5.0
(Claim 4). In this case, it is preferable that one side or both sides of the “plastic lens having negative refractive power” in the second lens group is aspherical.

  As shown in FIG. 1, the first lens group of the projection lens according to any one of claims 1 to 5 includes: “a first negative lens having a meniscus shape and aspheric surfaces on both sides in order from the enlargement side; It can be set as the structure which starts from "the structure which consists of a 2nd negative lens of a shape" (Claim 6). In the example of FIG. 1, a concave lens is arranged on the reduction side of the second negative lens.

  The configuration of the first lens group is preferably composed of “three negative lenses” as shown in Examples described later. In Examples 1 to 5, each of the three negative lenses constituting the first lens group is a negative lens having a concave surface having a strong curvature directed toward the reduction side, and the first lens counted from the enlargement side is light. The vicinity of the axis is a biconcave shape, the overall shape is a meniscus shape, the second lens is a negative meniscus lens, and the third lens is a biconcave lens.

  In the projection lens according to claim 6, the “first negative lens disposed on the most magnified side in the first lens group” can be made of plastic (claim 7), and in this case, the first lens It is preferable that the optical path length of the principal ray passing through the “air layer between the first and second negative lenses” in the group increases as the image height increases.

  Further, as described above, in the lens configuration of the second lens group in the projection lens according to any one of claims 1 to 8, as described above, "three pieces on the enlargement side" are the first negative lens and the first positive lens. Consists of a second positive lens, the first negative lens is bonded to the first positive lens, and one or two negative lenses having a small Abbe number are arranged on the reduction side of the second positive lens However, as a specific lens configuration of the second lens group, as shown in an example described later, from the enlargement side toward the reduction side, “negative positive (tangent 1) / positive / negative positive (tangent 2)”.・ Negative / Positive / Negative (tangent 3) / Positive / Positive ”(Examples 1-4) and“ Negative / Positive (tangent 1) / Positive / Positive / Positive / Negative (tangent 4) / Positive / Positive ”power arrangement Is preferred.

In the above description, “tangent 1” is a cemented lens of the first negative lens and the first positive lens.
Further, “tangent 2” to “tangent 4” are “a cemented lens in which a negative lens having a small Abbe number and a positive lens having a large Abbe number are bonded together”, and is used for correcting lateral chromatic aberration.
A projection-type image display device according to the present invention includes the projection lens according to any one of the first to eighth aspects of the present invention (claim 9).

  To supplement the explanation, it is necessary to shorten the focal length of a projection lens having a wide angle of view. However, if the focal length is shortened by reducing the lens surface interval and the radius of curvature as it is, the back focus is also shortened. .

  A retrofocus type projection lens used in a “rear projector using a reflective panel” requires a “long back focus” in which a PBS, a color synthesis prism, etc. can be arranged. The ratio (so-called “retro ratio”) must be large.

  In order to realize the “half angle of view: a wide angle of view of 40 degrees or more” aimed by the projection lens of the present invention, a retro ratio of 4 or more is generally required. The asymmetry of the refractive power distribution between the enlargement side and the reduction side with respect to the center is also increased. As described above, a projection lens for a rear projector using a reflective panel requires “a telecentric property on the reduction side”. Therefore, the refracting power of the positive lens group on the reduction side is required to be larger, Asymmetry of force distribution becomes remarkable, and it is difficult to correct distortion aberration and lateral chromatic aberration.

  In order to suppress the occurrence of chromatic aberration of magnification to a small extent, it is fundamental to construct a lens system with a lens made of “glass with a large Abbe number”. "The property of bending more than the d-line due to refraction" does not change, so it is not easy to obtain a projection lens with sufficiently small lateral chromatic aberration.

  In general, in a retro focus type projection lens, a negative lens with a small Abbe number is added to the positive lens group on the reduction side, and this negative lens generates a chromatic aberration of magnification opposite to that of the positive lens. The lateral chromatic aberration is reduced as a whole by canceling the lateral chromatic aberration due to the above. However, glass with a small Abbe number has a large partial dispersion ratio. Even if the chromatic aberration of magnification with respect to the F-line is canceled and corrected sufficiently small, the g-line having a wavelength shorter than that of the F-line is overcorrected. Is generated.

  Thus, even from the viewpoint of correcting the lateral chromatic aberration, it has been difficult to realize a projection lens having both a wide angle of view and a large retro ratio.

  The projection lens according to the present invention includes, in the second lens group having a positive refractive power, a “junction lens of a first negative lens having a large curvature on the reduction side and a first positive lens having a large curvature on the enlargement side. The chromatic aberration of magnification is made small by having the “configuration consisting of a second positive lens having a large curvature on the enlargement side”.

  The g-line and F-line incident on the projection lens from one point on the enlargement side and emitted to the reduction side of the first lens group (considering a light beam traveling from one point on the screen to the panel) are d-lines with longer wavelengths. Going further on the optical axis side, the g-line with a short wavelength is reversed by the “negative lens with a small Abbe number added for correcting lateral chromatic aberration” on the reduction side of the second positive lens in the second lens group. The correction is overcorrected and proceeds away from the optical axis from the d line.

  In the projection lens according to the present invention, by providing the “second positive lens in the second lens group” that satisfies the condition (2), the action of bending the overcorrected g-line toward the optical axis side from the d-line. ", And the above-mentioned" chromatic aberration of magnification caused by overcorrection "is made small.

If the Abbe number of the second positive lens: ν _II3 exceeds the upper limit of the condition (2), it is difficult to suppress “the lateral chromatic aberration of light having a short wavelength” that occurs due to overcorrection. If the lower limit of the condition (2) is exceeded, the target aberration correction is possible, but in reality such optical glass is not known. Even if it exists, it will be expensive.

  The “junction lens in which the first negative lens and the first positive lens are bonded” in the second lens group corrects spherical aberration, coma aberration, and astigmatism generated by the strong refractive power of the second positive lens. Is for. By disposing this cemented lens on the “aperture stop side from the second positive lens”, the height of the principal ray (distance from the optical axis) in the cemented lens is reduced, and the lateral chromatic aberration, which is an off-axis aberration, is reduced. The impact is small. For this reason, the cemented lens can correct spherical aberration, coma aberration, and astigmatism without impairing the effect of the second positive lens. Also, axial chromatic aberration can be corrected by appropriately selecting the Abbe number of the cemented lens.

If the upper limit of the condition (1) is exceeded, the difference in refractive index between the first negative lens and the first positive lens: N ₁ −N ₂ becomes large. The curvature of the bonding surface becomes small and it becomes difficult to correct various aberrations. If the lower limit of the condition (1) is exceeded, the curvature of the bonded surface becomes too large, making it difficult to manufacture the lens.

  The refractive index of the optical glass used as the lens material differs depending on the wavelength of light. The shorter the wavelength, the larger the refractive index. The “degree of increasing the refractive index as the wavelength becomes shorter” is also different for each optical glass type.

Refractive index for g-line (435.83 nm) is Ng,
The refractive index for F-line (486.13 nm) is NF,
The refractive index for C line (656.27 nm) is NC,
the Abbe number for the d-line (587.56 nm) as ν _d ,
And the degree of increase in the refractive index between g-line and F-line is θ _gF , θ _gF is
θ _gF = (Ng−NF) / (NF−NC)
And is called “partial dispersion ratio”.

When plotting the (ν _d , θ _gF ) value of each optical glass in the “coordinate system with the partial dispersion ratio: θ _gF on the vertical axis and the Abbe number: ν _d on the horizontal axis”, most of them are distributed on a straight line. These optical glasses are called “normally dispersed glasses”. If the standard line is “one straight line connecting the coordinates of two optical glasses representing normal dispersion glass” on the coordinate system, there are some optical glasses whose coordinate points are relatively far from the standard line, These are called “anomalous dispersion glasses”.

The "deviation amount from the standard line" of anomalous dispersion glass is called "anomalous dispersion"
θ _gF − (0.6438−0.001682ν _d )
Defined by In the projection lens of the present invention, the material of the second positive lens arranged in the second lens group (partial dispersion ratio: θ _gF , Abbe number: ν _d = ν _II3 ), and the anomalous dispersion degree is a condition ( By selecting appropriately so as to satisfy 3), it is possible to further correct lateral chromatic aberration.

Parameters: θ _gF - (0.6438-0.001682ν _II3) condition (3) exceeds the lower limit of the "larger degree of refractive index for short light wavelength" in the second positive lens is reduced "overcorrected The effect of canceling out the lateral chromatic aberration that occurs in the above is weakened. If the upper limit of the condition (3) is exceeded, the effect of aberration correction increases, but such an optical glass is not known within a range that satisfies the condition (2).

  The condition (4) is a condition for ensuring a sufficient back focus necessary for the projection lens of the rear projector using the reflective panel while maintaining a desired “large field angle”.

  Half field angle: When the lower limit of the condition (4) is exceeded while maintaining a wide field angle of 40 degrees or more, the back focus: Bf becomes short, and between the projection lens and the reflective panel, PBS, color synthesis prism, etc. It becomes difficult to arrange the optical system. Further, if the upper limit of the condition (4) is exceeded while maintaining the desired “sufficient back focus”, the focal length f of the entire system becomes small, and it becomes difficult to correct various aberrations.

  Condition (5) is a condition for achieving both a sufficiently long back focus and good optical performance. If the parameter: | f1 / f | exceeds the upper limit of the condition (5), | f1 | becomes too large, the negative refractive power of the first lens group becomes small, and it becomes difficult to obtain a desired back focus. If the lower limit of condition (5) is exceeded, the back focus can be secured sufficiently, but | f1 | becomes too small and the negative refractive power of the first lens group becomes excessive, and aberrations such as coma and field curvature are reduced. It becomes difficult to keep good.

  The second lens group preferably has “a large Abbe number of the positive lens disposed on the reduction side” in order to suppress the occurrence of lateral chromatic aberration. However, if the anomalous dispersion is increased, the lateral chromatic aberration that occurs due to overcorrection described above. It is also effective against.

The projection lens of the present invention also uses a positive lens made of glass with a large Abbe number and anomalous dispersion on the reduction side of the second lens group.
A glass having a large Abbe number and anomalous dispersion has a larger “refractive index change due to temperature” than a normal optical glass, and the projection lens has a problem of “change in focus position due to temperature”. The “direction of refractive index change with temperature” is also opposite to that of normal optical glass, and this property has a serious effect on “change in focus position with temperature”.

  A negative lens with a small Abbe number arranged in the second lens group has a refractive index that increases as the temperature rises, so that the negative refractive power also increases. However, in a positive lens having a large Abbe number and anomalous dispersion, the refractive index decreases and the positive refractive power decreases as the temperature rises.

  For this reason, the refractive power of the entire projection lens is influenced by the positive and negative lenses when the temperature rises, and the “change in focus position due to temperature” becomes large.

  Since the projection lens for the rear projector is installed in the projector housing and then sealed in the housing, readjustment of the focus position is mechanically difficult, and it is necessary to pay sufficient attention to changes in the focus position.

  In view of this point, the condition (6) is a condition for disposing a plastic lens having a negative refractive power in the second lens group and restricting “change in focus position due to temperature”.

  As optical plastic materials, PMMA (methacrylic resin), COP (cycloolefin resin) and the like are known, but the refractive index of these plastics decreases as the temperature rises.

  The negative plastic lens disposed in the second lens group has a refractive index that decreases as the temperature rises, so the negative refractive power also decreases. As a positive lens having a large Abbe number and anomalous dispersion, It acts to counteract the “reduction in refractive power”.

If the parameter of condition (6): | f _P / f2 | exceeds the upper limit, the refractive power of the plastic lens becomes small, and the action of “offset of refractive power fluctuation accompanying temperature change” also becomes small. On the other hand, if the lower limit is exceeded, the refractive power of the plastic lens increases and the effect of “cancellation of refractive power fluctuation accompanying temperature change” becomes too large.

  In the projection lens according to claim 5, it is possible to realize high optical performance by providing an aspherical surface to the plastic lens disposed in the second lens group by utilizing the ease of processing of the plastic lens. I have to.

As described above, the refractive power distribution of the retrofocus type projection lens is asymmetric when viewed from the lens center (aperture stop position), and distortion is likely to occur greatly.
7. The projection lens according to claim 6, wherein the aspherical lens is arranged on the most enlarged side of the first lens group in which the height of the off-axis principal ray is larger than that of other lenses, so that distortion can be effectively prevented. It is corrected to.

  In the projection lens according to the seventh aspect, the aspherical lens in the first lens group can be reduced in cost as a “plastic aspherical lens” made of a plastic material that is inexpensive and easy to mold.

  As one of the causes for deteriorating the image quality of the projection image by the projection lens, there are so-called ghost and flare in which light rays are reflected by multiple lens surfaces and reflected on the screen. When ghosts and flares occur, the contrast of the projected image decreases, making it difficult to see. Conventionally, as a means for preventing ghosts and flares, a coating that lowers the reflectance is applied to each surface of the lens, but the required reflectance after coating is about 0.3%. small.

  Glass lenses can be coated with a good anti-reflective coating, but plastic lenses cannot be coated at ideal process temperatures due to their poor heat resistance. Realization of “coating” is difficult. Therefore, it is necessary for a projection lens equipped with a plastic lens to pay sufficient attention to how light rays reflected by the plastic surface travel.

  In the projection lens according to claim 8, the curvature of the lens surface adjacent to the reduction side of the plastic lens of the first lens group is increased, and the optical path length of the principal ray passing through the air layer between these lenses is set as the image height. It is increased with increase of ghost and flare is avoided.

  21 and 22 show light paths of light rays that are reflected by the plastic lens of the first lens group I, reflected again by the lens surface adjacent to the reduction side, and proceed to the screen.

  In the projection lens according to claim 8, as shown in FIG. 21, most of the reflected light hits the outer peripheral portion of the plastic lens (the lens on the most screen side in the figure) and cannot reach the screen, and ghost and flare may occur. Is decreasing.

  In a lens that does not satisfy the condition of claim 8, as shown in FIG. 22, the curvature of the glass lens adjacent to the reduction side of the plastic lens is small, and the reflected light beam goes directly to the screen, and ghost and flare are likely to occur. It is a projection lens.

  As described above, according to the present invention, as in a specific example described later, a half angle of view: a wide angle of view of 40 degrees or more, a long back focus, a reduction side has high telecentricity, A projection lens having a small chromatic aberration of magnification and good performance and a projection type image display apparatus equipped with the same can be realized.

  Hereinafter, five specific examples of the projection lens will be given as embodiments.

  In each embodiment, “S” represents the surface number counted from the enlargement side, and “R” represents the radius of curvature of each surface (including the surface of the aperture stop ST and the surface of PBS and the prism P that is a color synthesis optical system). (Paraxial radius of curvature in the case of an aspherical surface), and “D” represents a surface interval on the optical axis. Further, “Nd” and “νd” indicate “refractive index” and “Abbe number” with respect to the d-line of the material of each lens.

  “F” is the focal length of the entire projection lens system, “F / No” is the F value representing brightness, “ω” is the half angle of view, and “obd” is the first surface of the lens (first) from the object (screen) The distance to the lens surface on the most screen side of one lens group, “Bf”, represents the back focus in the air (without the prism). The unit of the quantity having a length dimension is “mm” unless otherwise specified.

The aspherical shape has an intersection with the optical axis as the origin, height relative to the optical axis: h, optical axis direction shift: Z, paraxial radius of curvature: R, conic constant: K, aspheric coefficient of higher order terms: As A, B, C, D, E, the well-known formula:
Z = (1 / R) · h ² / [1 + √ {1- (1 + K) · (1 / R) ² · h ² }]
+ A ・ h ⁴ + B ・ h ⁶ + C ・ h ⁸ + D ・ h ¹⁰ + E ・ h ¹²
The shape is specified by giving R, K, A, B, C, D, and E.

FIG. 1 shows the lens configuration of the projection lens of Example 1.
A first lens group I, an aperture stop ST, and a second lens group II are arranged from the enlargement side (left side of the figure). Between the projection lens and the reflection type panel RP, a prism P “which combines PBS and a color synthesis optical system” is inserted.

f = 8.527, F / No = 2.5, ω = 41.8 °, obd = 694,
Bf = 53.356
S R D Nd νd
1 −675.118 6.400 1.49154 57.8
2 93.241 6.500
3 45.000 3.200 1.72342 38.0
4 24.610 19.500
5 −81.193 2.400 1.48749 70.4
6 44.008 70.310
7 ∞ (Aperture) 4.190
8 −58.831 5.000 1.77250 49.6
9 15.850 6.250 1.59270 35.5
10 −97.160 0.370
11 34.300 4.990 1.80809 22.8
12 −113.222 4.410
13 −46.470 4.500 1.83500 43.0
14 48.974 7.420 1.48749 70.4
15 −19.888 0.450
16 −97.999 2.500 1.49154 57.8
17 109.212 0.300
18 58.455 8.170 1.49700 81.6
19 −18.050 1.500 1.80610 33.3
20 38.760 0.480
21 43.396 7.450 1.48749 70.4
22 −39.126 0.300
23 92.321 8.380 1.49700 81.6
24 −29.512 5.000
25 ∞ 72.000 1.51680 64.2
26 ∞ 0.987.

Aspherical first surface K = −2993.6407, A = 0.651265 × 10 ⁻⁵ , B = −0.467722 × 10 ⁻⁸ ,
C = 0.290651 × 10 ⁻¹¹ , D = −0.112668 × 10 ⁻¹⁴ , E = 0.196047 × 10 ⁻¹⁸
Second surface K = 0.395782, A = 0.40642 × 10 ⁻⁵ , B = −0.25603 × 10 ⁻⁸ ,
C = −0.992903 × 10 ⁻¹⁴ , D = 0.287208 × 10 ⁻¹⁵ , E = −0.132122 × 10 ⁻¹⁹
16th surface K = 30.933055, A = −0.576209 × 10 ⁻⁵ , B = 0.239836 × 10 ⁻⁷ ,
C = −0.201146 × 10 ⁻⁹ , D = 0.134849 × 10 ⁻¹¹ , E = −0.201298 × 10 ⁻¹⁴ .

Parameter values for each condition (1) N ₁ −N ₂ = 0.1798
(2) ν _II3 = 22.8
_{(3) θ gF - (0.6438-0.001682ν} II3) = 0.026
(4) Bf / f = 6.257
(5) | f1 / f | = 2.683
(6) | f _P /f2|=2.656.

  FIG. 2 shows a diagram of spherical aberration, astigmatism, and distortion obtained by evaluating the projection lens of Example 1 on the reduction side, and FIG. 3 shows a diagram of coma aberration. Each aberration diagram shows the aberration of green light: G having a wavelength of 550 nm. The spherical aberration diagram and the coma aberration diagram show red light: R, blue light: B, and wavelengths: 620 nm and 460 nm. Aberrations are also displayed. In the astigmatism diagram, S represents the sagittal image surface, and M represents the aberration of the meridional image surface.

  FIG. 4 shows a chromatic aberration of magnification in a wavelength range from 400 nm to 700 nm with 550 nm as a reference. Three image heights of 50%, 70%, and 10% are displayed, and the unit of the aberration value is micron.

  FIG. 5 shows the lens configuration of the projection lens of Example 2 according to FIG.

f = 8.572, F / No = 2.5, ω = 41.7 °, obd = 700,
Bf = 52.037
S R D Nd νd
1 −4255.808 5.800 1.49154 57.8
2 94.241 6.500
3 44.500 3.200 1.72342 38.0
4 21.750 18.500
5 −56.512 3.000 1.48749 70.4
6 63.990 61.800
7 ∞ (Aperture) 2.210
8 −66.251 5.000 1.75500 52.3
9 14.620 6.270 1.59270 35.5
10 −94.260 0.890
11 32.746 5.000 1.84666 23.8
12 −144.649 3.140
13 −50.885 3.610 1.83500 43.0
14 37.061 7.880 1.48749 70.4
15 −19.173 0.300
16 −85.099 2.500 1.49154 57.8
17 137.788 1.040
18 115.625 8.210 1.49700 81.6
19 −16.128 1.610 1.80610 33.3
20 40.583 0.500
21 46.963 8.439 1.48749 70.4
22 −31.039 0.300
23 93.801 9.290 1.49700 81.6
24 −29.091 5.000
25 ∞ 70.000 1.51680 64.2
26 ∞ 0.987.

Aspherical first surface K = −33835588030, A = 0.862689 × 10 ⁻⁵ , B = −0.522652 × 10 ⁻⁸ ,
C = 0.292579 × 10 ⁻¹¹ , D = −0.105813 × 10 ⁻¹⁴ , E = 0.209939 × 10 ⁻¹⁸
Second surface K = 2.319705, A = 0.555814 × 10 ⁻⁵ , B = −0.314258 × 10 ⁻⁸ ,
C = −0.352251 × 10 ⁻¹² , D = 0.245925 × 10 ⁻¹⁵ , E = −0.145401 × 10 ⁻¹⁸
16th surface K = 28.874395, A = −0.542325 × 10 ⁻⁵ , B = 0.348419 × 10 ⁻⁷ ,
C = −0.186021 × 10 ⁻⁹ , D = 0.150667 × 10 ⁻¹¹ , E = −0.276152 × 10 ⁻¹⁵ .

Parameter value of each condition (1) N ₁ −N ₂ = 0.1623
(2) ν _II3 = 23.8
_{(3) θ gF - (0.6438-0.001682ν} II3) = 0.014
(4) Bf / f = 6.071
(5) | f1 / f | = 2.542
(6) | f _P / f 2 | = 2.777
FIG. 6 shows a diagram of spherical aberration, astigmatism, and distortion obtained by evaluating the projection lens of Example 2 on the reduction side, FIG. 7 shows a diagram of coma aberration, and FIG. 8 shows a diagram of chromatic aberration of magnification.

  FIG. 9 shows the lens configuration of the projection lens of Example 3 according to FIG.

f = 8.012, F / No = 2.5, ω = 43.5 °, obd = 650,
Bf = 50.700
S R D Nd νd
1 −411.185 6.400 1.49154 57.8
2 93.241 6.500
3 45.000 3.640 1.72342 38.0
4 24.764 21.810
5 −90.360 3.000 1.49700 81.6
6 40.445 68.720
7 ∞ (Aperture) 0.570
8 −51.126 5.000 1.77250 49.6
9 16.506 5.830 1.59270 35.5
10 −76.403 0.300
11 33.987 5.000 1.75211 25.1
12 −76.007 5.510
13 −38.118 2.000 1.83500 43.0
14 57.087 7.130 1.48749 70.4
15 −19.031 1.650
16 −79.862 2.500 1.49154 57.8
17 406.376 0.300
18 131.419 7.280 1.49700 81.6
19 -18.060 3.560 1.80610 33.3
20 47.939 0.630
21 59.121 7.620 1.49700 81.6
22 −32.831 0.820
23 92.969 8.630 1.49700 81.6
24 −30.431 5.000
25 ∞ 68.000 1.51680 64.2
26 ∞ 0.962.

Aspherical first surface K = −1269.633, A = 0.646642 × 10 ⁻⁵ , B = −0.471781 × 10 ⁻⁸ ,
C = 0.288715 × 10 ⁻¹¹ , D = −0.113575 × 10 ⁻¹⁴ , E = 0.187275 × 10 ⁻¹⁸
Second surface K = 0.75227, A = 0.461252 × 10 ⁻⁵ , B = −0.293279 × 10 ⁻⁸ ,
C = −0.200867 × 10 ⁻¹² , D = 0.402215 × 10 ⁻¹⁵ , E = 0.353681 × 10 ⁻¹⁹
16th surface K = 31.65228, A = −0.724794 × 10 ⁻⁵ , B = 0.25797 × 10 ⁻⁷ ,
C = −0.199252 × 10 ⁻⁹ , D = 0.15029 × 10 ⁻¹¹ , E = 0.485537 × 10 ⁻¹⁵ .

Parameter values for each condition (1) N ₁ −N ₂ = 0.1798
(2) ν _II3 = 25.1
_{(3) θ gF - (0.6438-0.001682ν} II3) = 0.016
(4) Bf / f = 6.328
(5) | f1 / f | = 2.705
(6) | f _P /f2|=3.542
The spherical aberration, astigmatism, and distortion aberration of the projection lens of Example 3 evaluated on the reduction side are shown in FIG. 10, the coma aberration chart is shown in FIG. 11, and the lateral chromatic aberration chart is shown in FIG.

  FIG. 13 shows the lens configuration of the projection lens of Example 4 according to FIG.

f = 8.009, F / No = 2.5, ω = 43.5 °, obd = 650,
Bf = 53.361
S R D Nd νd
1 −426.945 5.800 1.49154 57.8
2 93.241 6.500
3 45.000 3.200 1.72342 38.0
4 25.123 20.400
5 −89.721 2.100 1.49700 81.6
6 41.377 70.450
7 ∞ (Aperture) 3.410
8 −57.202 5.000 1.77250 49.6
9 15.480 6.660 1.59270 35.5
10 −101.515 0.930
11 39.020 4.470 1.92286 20.9
12 −230.942 4.590
13 −55.089 4.480 1.83500 43.0
14 50.984 7.280 1.48749 70.4
15 −19.891 0.300
16 −97.773 2.500 1.49154 57.8
17 210.448 0.300
18 77.351 7.750 1.49700 81.6
19 -18.184 2.190 1.80610 33.3
20 38.871 0.490
21 43.751 7.420 1.48749 70.4
22 −39.141 0.320
23 92.323 8.460 1.49700 81.6
24 −29.169 5.000
25 ∞ 72.000 1.51680 64.2
26 ∞ 0.986.

Aspherical first surface K = −1555.7916, A = 0.70656 × 10 ⁻⁵ , B = −0.473154 × 10 ⁻⁸ ,
C = 0.289595 × 10 ⁻¹¹ , D = −0.112056 × 10 ⁻¹⁴ , E = 0.199129 × 10 ⁻¹⁸
Second surface K = 1.114313, A = 0.459977 × 10 ⁻⁵ , B = −0.2748 × 10 ⁻⁸ ,
C = −0.866238 × 10 ⁻¹³ , D = 0.283554 × 10 ⁻¹⁵ , E = 0.276454 × 10 ⁻¹⁹
16th surface K = 31.038295, A = −0.5659 × 10 ⁻⁵ , B = 0.230742 × 10 ⁻⁷ ,
C = −0.205065 × 10 ⁻⁹ , D = 0.136584 × 10 ⁻¹¹ , E = −0.201709 × 10 ⁻¹⁴ .

Parameter values for each condition (1) N ₁ −N ₂ = 0.1798
(2) ν _II3 = 20.9
_{(3) θ gF - (0.6438-0.001682ν} II3) = 0.0282
(4) Bf / f = 6.663
(5) | f1 / f | = 2.802
(6) | f _P /f2|=3.572
FIG. 14 shows a diagram of spherical aberration, astigmatism, and distortion obtained by evaluating the projection lens of Example 4 on the reduction side, FIG. 15 shows a diagram of coma aberration, and FIG. 16 shows a diagram of chromatic aberration of magnification.

  FIG. 17 shows the lens configuration of the projection lens of Example 5 following FIG.

  In Example 5, the second lens group is composed entirely of spherical lenses, but has good optical performance as can be seen from the aberration diagrams. If it is judged that it can sufficiently withstand the “change in focus position due to temperature” on the assumption that it will be used in an environment where the temperature change is relatively small, a negative plastic lens is installed in the second lens group. Therefore, it is possible to realize a projection lens with a low price.

f = 6.687, F / No = 2.5, ω = 46.8 °, obd = 585,
Bf = 32.288
S R D Nd νd
1 417.151 5.000 1.49154 57.8
2 57.965 5.200
3 36.817 2.800 1.77250 49.6
4 25.980 13.020
5 −235.980 2.100 1.62041 60.3
6 22.365 78.150
7 ∞ (Aperture) 0.300
8 133.375 1.300 1.74330 49.2
9 13.897 5.410 1.59270 35.5
10 −98.151 9.180
11 19.444 3.760 1.75520 27.5
12 25.420 2.760
13 −40.797 4.040 1.48749 70.4
14 −21.060 3.330
15 64.065 6.560 1.49700 81.6
16 −13.811 1.300 1.80610 33.3
17 32.885 0.600
18 48.170 5.190 1.48749 70.4
19 −38.244 0.300
20 38.531 6.120 1.49700 81.6
21 −35.341 5.000
22 ∞ 40.000 1.51680 64.2
23 ∞ 0.989.

Aspheric surface 1st surface K = 71.043882, A = 0.13487 × 10 ⁻⁴ , B = −0.157696 × 10 ⁻⁷ ,
C = 0.145349 × 10 ⁻¹⁰ , D = −0.792813 × 10 ⁻¹⁴ , E = 0.223574 × 10 ⁻¹⁷
Second surface K = 0.648548, A = 0.102198 × 10 ⁻⁴ , B = −0.102875 × 10 ⁻⁷ ,
C = −0.660603 × 10 ⁻¹¹ , D = 0.170581 × 10 ⁻¹³ , E = −0.79222 × 10 ⁻¹⁷
Condition parameter values (1) N ₁ −N ₂ = 0.1506
(2) ν _II3 = 27.5
_{(3) θ gF - (0.6438-0.001682ν} II3) = 0.010
(4) Bf / f = 4.828
(5) | f1 / f | = 2.811
FIG. 18 shows a diagram of spherical aberration, astigmatism, and distortion obtained by evaluating the projection lens of Example 5 on the reduction side, FIG. 19 shows a diagram of coma aberration, and FIG. 20 shows a diagram of chromatic aberration of magnification.

In any of the projection lenses of Examples 1 to 5 described above, from the enlargement side toward the reduction side, the first lens group I having a negative refractive power, the aperture stop ST, and the second lens group having a positive refractive power. II is arranged and is telecentric on the reduction side, and the second lens group II is composed of “a first negative lens having a large curvature on the reduction side in order from the enlargement side, and a first positive lens having a large curvature on the enlargement side. “Composition consisting of a cemented lens in which two lenses are bonded together and a second positive lens having a large curvature on the enlargement side” and a smaller Abbe number of one or two on the reduction side than the second positive lens The negative lens is arranged as a cemented lens (two cemented lenses in Examples 1 to 4 and one cemented lens in Example 5) bonded to a positive lens having a larger Abbe number, and the refractive index of the first negative lens: N ₁ , refractive index of first positive lens: N ₂ The Abbe number of the second positive lens: ν _II3 is the condition:
_{(1) 0.13 <N 1 -N} 2 <0.20
(2) 15 < _νII3 <30
(Claim 1).

In the projection lenses of Examples 1 to 5, the Abbe number of the third positive lens: ν _{II3 and the} partial dispersion ratio: θ _gF are as _follows :
_{(3) 0 <θ gF -} (0.6438-0.001682ν II3) <0.04
(Claim 2), the back focus: Bf, the focal length of the entire system: f, and the focal length: f1 of the first lens group are:
(4) 4.0 <Bf / f <6.8
(5) 2.4 <| f1 / f | <3.0
(Claim 3).

The projection lenses of Examples 1 to 4 include one negative plastic lens in the second lens group II. The focal length of the plastic lens is f _P and the focal length of the second lens group is f2. conditions:
(6) 2.5 <| f _P /f2|<5.0
(Claim 4) and the surface of the plastic lens is aspherical (Claim 5).

  In each of the projection lenses of Examples 1 to 5, the first lens group I starts with the first negative lens having a meniscus shape and aspherical surfaces on both sides in order from the enlargement side, and the second negative lens having a meniscus shape. Item 6) The material of the first negative lens is plastic (Claim 7).

  In any of the projection lenses of Examples 1 to 5, the optical path length of the chief ray passing through the air layer between the first and second negative lenses in the first lens group becomes larger as the image height increases. Therefore, the light of the white light source is separated into three lights of red, green, and blue, led to three independent reflective panels, and the image information reflected from each reflective panel is obtained. By mounting the projection lens of Examples 1 to 5 on a projection type image display device such as a well-known rear projector that synthesizes light with a prism of a color synthesis optical system and displays an enlarged projection from the back of a transmission type screen. A projection type image display device capable of displaying a high-definition image can be realized.

1 is a lens configuration diagram of Example 1. FIG. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration of Example 1. FIG. 6 is a diagram showing coma aberration in Example 1. FIG. 3 is a diagram showing chromatic aberration of magnification of Example 1. 6 is a lens configuration diagram of Example 2. FIG. It is a figure which shows the spherical aberration of Example 2, astigmatism, and a distortion aberration. FIG. 6 is a diagram showing coma aberration in Example 2. FIG. 5 is a diagram showing chromatic aberration of magnification of Example 2. 6 is a lens configuration diagram of Example 3. FIG. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration of Example 3. FIG. 6 is a diagram showing coma aberration in Example 3. FIG. 6 is a diagram showing lateral chromatic aberration in Example 3. 6 is a lens configuration diagram of Example 4. FIG. It is a figure which shows the spherical aberration of Example 4, astigmatism, and a distortion aberration. FIG. 6 is a diagram showing coma aberration in Example 4. FIG. 6 is a diagram showing lateral chromatic aberration in Example 4. FIG. 6 is a lens configuration diagram of Example 5. It is a figure which shows the spherical aberration of Example 5, astigmatism, and a distortion aberration. FIG. 6 is a diagram showing coma aberration in Example 5. FIG. 10 is a diagram showing chromatic aberration of magnification of Example 5. It is a 1st lens group of Claim 8, It is a figure which once reflects between the plastic lens and the lens surface adjacent to it, and shows the light ray which goes to a screen. It is a 1st lens group which does not satisfy | fill the conditions of Claim 8, It is a figure which reflects once between a plastic lens and the lens surface adjacent to it, and shows the light ray which goes to a screen.

Explanation of symbols

I First lens group
II Second lens group ST Aperture stop
P Prism RP reflection type panel combining PBS and color synthesis optical system

Claims (9)

A first lens group having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power are arranged in this order from the enlargement side toward the reduction side, and is telecentric on the reduction side.
The second lens group includes, in order from the magnification side, a cemented lens in which two lenses, a first negative lens having a large curvature on the reduction side and a first positive lens having a large curvature on the magnification side, are bonded to the magnification side. Starting with a composition consisting of a second positive lens with a large curvature,
And, on the reduction side of the second positive lens, one or two negative lenses having a small Abbe number are arranged alone or as a cemented lens bonded to a positive lens having a larger Abbe number,
Conditions are: refractive index of the first negative lens: N ₁ , refractive index of the first positive lens: N ₂ , Abbe number of the second positive lens: ν _{II3
(1) 0.13 <N 1 -N} 2 <0.20
(2) 15 < _νII3 <30
Projection lens characterized by satisfying The projection lens according to claim 1,
Condition of partial dispersion ratio θ _gF and Abbe number ν _II3 of the second positive lens in the second lens group:
_{(3) 0 <θ gF -} (0.6438-0.001682ν II3) <0.04
Projection lens characterized by satisfying The projection lens according to claim 1 or 2,
Conditions when the back focus in the air when the conjugate point on the magnification side is infinity: Bf, the focal length of the entire system: f, and the focal length of the first lens group: f1
(4) 4.0 <Bf / f <6.8
(5) 2.4 <| f1 / f | <3.0
Projection lens characterized by satisfying The projection lens according to any one of claims 1 to 3,
The second lens group includes one plastic lens having negative refractive power, and the focal length of the plastic lens is f _P and the focal length of the second lens group is f2.
(6) 2.5 <| f _P /f2|<5.0
Projection lens characterized by satisfying The projection lens according to claim 4,
A projection lens having a negative refractive power in the second lens group, wherein one or both surfaces are aspherical. In the projection lens according to any one of claims 1 to 5,
A projection lens, wherein the first lens group starts from a configuration including a first negative lens having a meniscus shape and aspheric surfaces on both sides and a second negative lens having a meniscus shape in order from the magnification side. The projection lens according to claim 6,
A projection lens, wherein the first negative lens arranged on the most enlarged side in the first lens group is made of plastic. The projection lens according to claim 7, wherein
A projection lens, wherein an optical path length of a chief ray passing through an air layer between a first negative lens and a second negative lens in the first lens group increases as the image height increases.   A projection-type image display device comprising the projection lens according to any one of claims 1 to 8.

Images