JPH0990219A - Projection lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a projection lens which suitably obtain video of high picture quality as a projection lens used for a projector device which enlarges and projects video from a cathode-ray tube on a large-sized screen. SOLUTION: This projection lens consists of four lens groups which are a 1st lens group GR1-a 4th lens group GR4 in order from a projection surface side; and the 1st lens group-the 3rd lens group GR3 have positive refracting power and the 4th lens group has negative refracting power. The 1st lens group and 3rd lens group are composed of acrylic lenses L1 and L2, and L4 and L5, the 2nd lens group GR2 is composed of a spherical glass lens L3, and the 4th lens group is composed of an acryl lens L6 which has a large-curvature concave surface on the projection surface side, a cathode-ray tube face plate 2, and cooling liquid 3 filling the part between the acryl lens and cathode-ray tube face plate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel projection lens. More specifically, the present invention relates to a projection lens suitable for obtaining a high quality image in a projection lens used for a projector device for enlarging and projecting an image from a cathode ray tube (hereinafter referred to as “CRT”) on a large screen. Is.

[0002]

2. Description of the Related Art In recent years, in order to enjoy television images, video images, etc. on a large screen, images on the fluorescent screens of red, blue, and green CRTs are enlarged and projected on the screen by projection lenses. Therefore, a so-called projector device that obtains a large-screen image by synthesizing the images composed of the above three colors of light is widely used.

In the above projector device, the performance of the optical system of the projection lens is particularly important in order to obtain a high quality image.

Such a projection lens is composed of, for example, three lens groups as disclosed in US Pat. Nos. 4,300,817 and 4,348,081, and is disclosed in US Pat. Nos. 4,697,892 and 4,682,862. In addition to the above-mentioned three lens groups, a new lens group called a correction unit is inserted between the second lens group and the third lens group so as to be configured by four lens groups. There is.

In general, in a projector device, it is necessary to widen the angle of view of the lens system of the projection lens to shorten the focal position in order to make the entire system compact. The latter is intended for this.

Further, in the projection lens disclosed in Japanese Patent Laid-Open No. 4-121704, a lens having most of the positive refracting power of the entire lens system is arranged in the third lens system, and the lens is used. A concave lens made of a high-dispersion glass material and a convex lens made of a low-dispersion glass material are bonded to each other, thereby reducing chromatic aberration and achieving a short focus.

Further, in the projection lens disclosed in Japanese Unexamined Patent Publication No. 6-258575, the number of lens systems is increased to suppress the occurrence of aberration and realize a short focus.

In the projection lens disclosed in Japanese Patent Laid-Open No. 7-49450, styrene, which is a highly dispersed plastic material, is used for the lens on the projection surface side of the first lens group, and the negative lens around the effective aperture is used. Color correction is performed by the refractive power.

[0009]

However, in the above-mentioned conventional projection lens, although the shortening of the focal length is almost achieved, other problems occur or are still unsolved.

That is, in the projection lens disclosed in Japanese Patent Application Laid-Open No. 4-121704, since the concave lens made of the high dispersion glass material and the convex lens made of the low dispersion glass material are used, the production cost becomes high and the short focus Even if it is made smaller, the half angle of view is insufficient at about 34 degrees, and there is a problem that it does not contribute much to downsizing of the entire apparatus.

Further, in the projection lens disclosed in Japanese Unexamined Patent Publication No. 6-258575, since the residual amount of chromatic aberration is still large and a lens having a small amount of aspherical surface is used, the peripheral light flux is corrected. There was a problem of running out.

In the projection lens disclosed in Japanese Unexamined Patent Publication No. 7-49450, styrene, which is the material of the lens used for the projection lens, has a large birefringence, a soft surface, a low heat resistant temperature, etc. There is a problem
It was unsuitable as a lens material.

As described above, conventionally, it has been difficult to obtain a high-quality image in which various aberrations are corrected with a projection lens in which the focal point of the lens system is short.

[0014]

In view of the above-mentioned various problems, the projection lens of the present invention is configured by four lens groups of a first lens group to a fourth lens group in order from the projection surface side.
In the projection lens in which each of the lens group to the third lens group has a positive refractive power and the fourth lens group has a negative refractive power, the first lens group and the third lens group are formed by a plurality of acrylic lenses. The second lens group is composed of a spherical glass lens, and the fourth lens group is filled between the acrylic lens and the cathode ray tube face plate with the strong concave surface facing the projection surface and between the acrylic lens and the cathode ray tube face plate. It is composed of the cooled liquid.

Therefore, in the projection lens of the present invention, only the second lens group is composed of the spherical glass lens and the other lens groups are composed of the acrylic lens, so that the wide angle of view and the aberration can be obtained. In particular, it is possible to obtain a projection lens in which color flare is appropriately corrected without increasing the production cost.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The projection lens of the present invention will be described below with reference to the illustrated embodiments.

First, the basic structure of the projection lens of the present invention, which is common to the respective embodiments described later, will be described.

FIG. 1, FIG. 4, and FIG.
Of the projection lens 1, 1A and 1
B is the first in order from the screen (projection surface) side not shown.
Lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6 and CRT
The face plate 2 is arranged, and further the sixth lens L6
The cooling liquid 3 is filled between the CRT face plate 2 and the CRT face plate 2.

The first lens L1 to the sixth lens L6
S ₁ the surface, from the screen side in the order of, S _2, ···, S
₁₂ , the surface of the CRT face plate 2 is S ₁₃ , CR
The fluorescent surface of T is S ₁₄ .

The projection lenses 1, 1A and 1B are the first
The lens L1 and the second lens L2 form a first lens group GR1, the third lens L3 forms a second lens group GR2, and the fourth lens L4 and the fifth lens L5 form a third lens group GR3. Similarly, the sixth lens L6, the CRT face plate 2 and the cooling liquid 3 are used to form the fourth lens group G.
It constitutes R4.

Further, the refracting power of each lens group has a first lens group GR1, a second lens group GR2 and a third lens group GR3.
Is positive, and the fourth lens group GR4 is negative.

In the following description, S _i is the i-th lens surface counted from the projection surface (screen) side, r is the radius of curvature of each lens surface, d is the distance between two adjacent lens surfaces, Let n be the refractive index for light of a predetermined wavelength (587.6 nm), and v be the Abbe number for light of a predetermined wavelength (587.6 nm).

The projection lenses 1, 1A and 1 of the present invention are
B satisfies the following conditions.

In general, the aspherical shape of the lens surface has a deviation Z from the tangential plane at the apex of the lens surface in the optical axis direction.
, The distance from the optical axis is Y, the paraxial curvature is C, the conic coefficient is K, and the j-order aspherical coefficient is A _j (j = 4, 6, 8, 1).
0, 12, and 14. ) Is defined by the following equation.

[0025]

[Equation 1]

On a spherical lens surface, K and A _j can be neglected among the respective values of the above equation, so that when the deviation amount in the optical axis direction from the tangential plane at the apex of the lens surface is X, It is defined by the following formula derived from the formula.

[0027]

[Equation 2]

Therefore, from the above two equations, the deviation amount ΔS _i of the lens surface S _{i from} the reference spherical surface becomes Z−X, and ΔS _i is defined by the following equation.

[0029]

(Equation 3)

That is, when the focal length of the entire lens system of the first lens L1 is f ₀ and the focal length of the first lens group GR1 is f ₁ , f ₀ / f ₁ <0.4 (hereinafter, "condition 1 ".)
And the deviation amounts (aspherical shapes) of the lens surface S ₁ and the lens surface S _{2 from} the reference spherical surface are respectively ΔS ₁ and ΔS ₂
Then, 5 <ΔS ₂ −ΔS ₁ <13 (hereinafter, “condition 2”)
Say. ) Is satisfied.

The predetermined wavelength of the third lens L3 (58
If the Abbe number for light of 7.6 nm is ν _L3 , then ν
_It satisfies _L3 > 55 (hereinafter, referred to as “condition 3”).

Further, in the fifth lens L5, if the deviation amounts (aspherical shapes) of the projection surface side lens surface S ₉ and the CRT side lens surface S _{10 from} the reference spherical surface are ΔS ₉ and ΔS ₁₀ , respectively. 2 <ΔS ₁₀ −ΔS ₉ <4.0 (hereinafter, referred to as “condition 4”) is satisfied.

Here, f ₀ / in the above conditions 1 to 4
The values of f ₁ , ΔS ₂ −ΔS ₁ , ν _L3 and ΔS ₁₀ −ΔS ₉ are shown in Table 1 for each Example described later.

[0034]

[Table 1]

As shown in Table 1, it is apparent that the conditions 1 to 4 are satisfied in Examples 1 to 3.

Next, each of the above conditions will be described. Condition 1 defines the refractive power of the first lens L1.
When the value of f ₀ / f ₁ exceeds 0.4, in the projection lens of the present invention having a large aperture ratio, the correction of low-order spherical aberration is insufficient, and the high result at the center of the screen when projected on the screen. Image performance cannot be obtained.

Condition 2 defines the shape of the peripheral portion of the first lens L1. In the projection lens of the present invention, the shape of the peripheral portion of the first lens L1 causes the rays of light in the peripheral portion of the fluorescent screen of the CRT to change, In particular, it imparts a negative refracting power to a light ray below the principal ray, and works to suppress the occurrence of color flare (red and blue bleeding).

Therefore, when the value of ΔS ₂ -ΔS ₁ is 5 or less, the force acting as described above becomes weak and it becomes impossible to suppress the occurrence of color flare.

On the other hand, when the value of ΔS ₂ −ΔS ₁ exceeds 13, the coma flare is increased in the inner portion of the peripheral portion of the first lens L1, and the aberration balance in the entire lens system is increased. In addition, the lens shape becomes complicated, and the workability of the lens deteriorates.

Condition 3 defines the Abbe number of the third lens L3. The third lens L3 is the projection lens 1, 1A
Since it takes most of the positive refracting power in the entire lens system of 1B and 1B, for example, when the value of ν _L3 is lower than 55, axial chromatic aberration is significantly generated, and its correction is difficult. Will be.

Condition 4 defines the shape of the peripheral portion 7 of the fifth lens L5, and the fifth lens L5 defines the peripheral portion 7.
With this shape, a negative correction force is applied to a light ray in the peripheral portion of the phosphor screen of the CRT, particularly, a light ray above the principal ray to correct various aberrations.

Therefore, when the value of ΔS ₁₀ -ΔS ₉ becomes smaller than 2.2, the negative refraction component in the peripheral portion of the fifth lens L5 becomes insufficient and the color flare increases. By the way, when the shape of the peripheral portion of the fifth lens L5 is set such that the value of ΔS ₁₀ −ΔS ₉ is smaller than 2.2, the peripheral portion of the sixth lens L6 is negative in order to correct this. Of the sixth lens L6, it becomes difficult to correct coma flare.

On the contrary, the value of ΔS ₁₀ −ΔS ₉ is 4.
When it becomes larger than 0, the fifth lens L5 and the sixth lens L6
Is insufficient, and the interval for compensating the fluctuation of the focal position caused by the temperature change of the acrylic lens is insufficient.

Therefore, by satisfying the above conditions,
The projection lens of the present invention realizes a wide angle of view of 80 degrees or more, and is bright with an effective F value of about 1.15 and can obtain good image forming performance.

Next, the concrete shape of each lens in each embodiment satisfying the basic structure of the projection lens of the present invention will be described.

FIGS. 1 to 3 show the first embodiment 1.

The first lens L1 is a meniscus lens whose both surfaces are aspherical, and the surface S ₁ on the projection surface side has different surface shapes in the central portion and the peripheral portion. That is, the central portion forms a convex surface having a positive refractive power, and the peripheral portion forms a concave surface having a negative refractive power. The distance between the central portion and the peripheral portion gradually increases from the central portion to the peripheral portion side. The surface is such that the refractive power changes from the positive side to the negative side. The surface S on the CRT side
₂ is an aspherical concave surface.

The second lens L2 is a meniscus lens having positive refractive power and both surfaces of which are aspherical, and the surface S ₃ on the projection surface side is concave and the surface S ₄ on the CRT side is convex. is there.

The third lens L3 has a strong positive refractive power,
Both the surface S ₅ on the projection surface side and the surface S ₆ on the CRT side are convex surfaces having a spherical shape, and particularly the surface S ₅ on the projection surface side is a strong convex surface.

The fourth lens L4 is a meniscus lens whose both surfaces are aspherical, and the surface S ₇ on the projection surface side is a convex surface, while the surface S ₈ on the CRT side has a surface shape in the central portion and the peripheral portion. Is different. That is, the central portion forms a concave surface having a negative refractive power, the peripheral portion forms a convex surface having a positive refractive power, and the space between the central portion and the peripheral portion gradually increases the refractive power toward the peripheral portion side. Is a surface that changes from negative to positive side.

The fifth lens L5 is a meniscus lens whose both surfaces are aspherical, and the surface S ₉ on the projection surface side is a concave surface, but the surface S ₁₀ on the CRT side has a surface shape in the central portion and the peripheral portion. Is different. That is, the central portion forms a convex surface having a positive refractive power, the peripheral portion forms a concave surface having a negative refractive power, and between the central portion and the peripheral portion, the refractive power gradually increases toward the peripheral portion side. Is a surface that changes from the positive side to the negative side.

The sixth lens L6 is a meniscus lens in which the surface S ₁₁ on the projection surface side is an aspherical surface and is strongly concave, and the surface S ₁₂ on the CRT side is spherically shaped and strongly convex.

Table 2 shows r, d, n, and ν of the surfaces S _{1 to} S ₁₂ of the lenses L1 to L6 in the first embodiment.
Table 3 shows the values of S _{1 to} S ₄ and S ₇ that form the aspherical surface.
To S ₁₁ for K and A _j (j = 4, 6, 8, 10,
12 and 14), and an astigmatism diagram (solid line shows sagittal image plane, broken line shows meridional image plane) in FIG.
Transverse aberration diagram (solid line wavelength 546.1 nm, broken line wavelength 64)
3.9 nm, the alternate long and short dash line shows the value at 480.0 nm)
Is shown in FIG. In addition, ω indicates a half angle of view.

[0054]

[Table 2]

In Table 2, the focal length f ₀ of the entire lens system is 66.40, and the F number F _NO of the entire lens system is 1.
16, the magnification is -0.125.

[0056]

[Table 3]

FIGS. 4 to 6 show the second embodiment 1A of the projection lens of the present invention.

The first lens L1 is a meniscus lens whose both surfaces are aspherical, and the surface S ₁ on the projection surface side has different surface shapes in the central portion and the peripheral portion. That is, the central portion forms a convex surface having a positive refractive power, and the peripheral portion forms a concave surface having a negative refractive power. The distance between the central portion and the peripheral portion gradually increases from the central portion to the peripheral portion side. The surface is such that the refractive power changes from the positive side to the negative side. The surface S on the CRT side
₂ is concave.

The second lens L2 is a meniscus lens whose both surfaces are aspherical, and the surface S ₃ on the projection surface side has different surface shapes in the central portion and the peripheral portion. That is, the central portion has a concave surface having a negative refractive power and the peripheral portion has a convex surface having a positive refractive power, and the distance between the central portion and the peripheral portion gradually increases from the central portion toward the peripheral portion. The surface is such that the refractive power changes from negative to positive. The surface S on the CRT side
₄ is a convex surface.

The third lens L3 has a strong positive refractive power,
Both the surface S ₅ on the projection surface side and the surface S ₆ on the CRT side are convex surfaces having a spherical shape, and particularly the surface S ₅ on the projection surface side is a strong convex surface.

[0061] The fourth lens L4 is a meniscus lens having both surfaces with a non-spherical shape, the surface S ₈ surface S ₇ and the CRT of the projection surface side are both different from the plane shape between the center and periphery. That is, in the surface S ₇ , the central portion is a concave surface having a negative refractive power, and the peripheral portion is a convex surface having a positive refractive power, and the space between the central portion and the peripheral portion is from the central portion to the peripheral portion side. The surface is such that the refractive power gradually changes from negative to positive as it goes to. Further, in the surface S ₈ on the CRT side, the central portion is a convex surface having a positive refractive power, and the peripheral portion is a concave surface having a negative refractive power, and between the central portion and the peripheral portion, the central portion to the peripheral portion. The refractive power gradually changes from positive to negative as it goes to the side of the section.

The fifth lens L5 is a meniscus lens whose both surfaces are aspherical, and the surface S ₉ on the CRT side is a concave surface, but the surface S ₁₀ on the CRT side has a different surface shape between the central portion and the peripheral portion. ing. That is, the central portion forms a convex surface having a positive refractive power, the peripheral portion forms a concave surface having a negative refractive power, and the portion between the central portion and the peripheral portion gradually refracts toward the peripheral portion side. It is a surface where the force changes from the positive side to the negative side.

The sixth lens L6 is a meniscus lens in which the surface S ₁₁ on the projection surface side is an aspherical surface and is strongly concave, and the surface S ₁₂ on the CRT side is spherically shaped and strongly convex.

Table 4 shows r, d, n, and ν of the surfaces S _{1 to} S ₁₂ of the lenses L1 to L6 in the second embodiment.
The respective values of are shown in Table 5 as the surfaces S _{1 to} S ₄ and S ₇ forming the aspherical shape.
To S ₁₁ for K and A _j (j = 4, 6, 8, 10,
12 and 14), and an astigmatism diagram (solid line indicates sagittal image plane, broken line indicates meridional image plane) in FIG.
Transverse aberration diagram (solid line wavelength 546.1 nm, broken line wavelength 64)
3.9 nm, the alternate long and short dash line shows the value at 480.0 nm)
Is shown in FIG.

[0065]

[Table 4]

In Table 4, f ₀ = 66.40, F
_NO = 1.18, magnification = −0.1265.

[0067]

[Table 5]

7 to 9 show a third embodiment 1B of the projection lens of the present invention.

The first lens L1 is a meniscus lens whose both surfaces are aspherical, and the surface S ₁ on the projection surface side has different surface shapes in the central portion and the peripheral portion. That is, the central portion forms a convex surface having a positive refractive power, and the peripheral portion forms a concave surface having a negative refractive power. The distance between the central portion and the peripheral portion gradually increases from the central portion to the peripheral portion side. The surface is such that the refractive power changes from the positive side to the negative side. The surface S on the CRT side
₂ is concave.

The second lens L2 is a meniscus lens whose both surfaces are aspherical, and the surface S ₃ on the projection surface side has different surface shapes in the central portion and the peripheral portion. That is, the central portion has a concave surface having a negative refractive power and the peripheral portion has a convex surface having a positive refractive power, and the distance between the central portion and the peripheral portion gradually increases from the central portion toward the peripheral portion. The surface is such that the refractive power changes from negative to positive. The surface S on the CRT side
₄ is a convex surface.

The third lens L3 has a strong positive refractive power,
Both the surface S ₅ on the projection surface and the surface S ₆ on the CRT side are convex surfaces having a spherical shape, and particularly the surface S ₅ on the projection surface side is a strong convex surface.

The fourth lens L4 is a meniscus lens whose both surfaces are aspherical, and the surface S ₇ on the projection surface side and the surface S ₈ on the CRT side are different in surface shape between the central portion and the peripheral portion. That is, in the surface S ₇ , the central portion is an aspherical convex surface having a positive refractive power, and the positive refractive power gradually decreases from the central portion toward the peripheral portion. Has become. In the surface S ₈ on the CRT side, the central portion is an aspherical concave surface having negative refractive power, and the peripheral portion is an aspherical convex surface having positive refractive power. Between them, the surface is such that the refractive power gradually changes from negative to positive as it goes from the central part to the peripheral part.

The fifth lens L5 is a meniscus lens having an aspherical shape, and the surface S ₉ on the CRT side is concave,
The surface shape of the surface S ₁₀ on the CRT side is different between the central portion and the peripheral portion. That is, the central portion forms a convex surface having a positive refractive power, the peripheral portion forms a concave surface having a negative refractive power, and the portion between the central portion and the peripheral portion gradually refracts toward the peripheral portion side. It is a surface where the force changes from the positive side to the negative side.

In the sixth lens L6, the surface S ₁₁ on the projection surface side is an aspherical surface and is strongly concave, and the surface S ₁₂ on the CRT side is spherical and strongly convex.

Table 6 shows r, d, n, and υ of the surfaces S _{1 to} S ₁₂ of the lenses L1 to L6 in the third embodiment.
The respective values of are shown in Table 7 as the surfaces S _{1 to} S ₄ and S ₇ forming the aspherical shape.
To S ₁₁ for K and A _j (j = 4, 6, 8, 10,
12 and 14), and an astigmatism diagram (solid line indicates sagittal image plane, broken line indicates meridional image plane) in FIG.
Transverse aberration diagram (solid line wavelength 546.1 nm, broken line wavelength 64)
3.9 nm, the alternate long and short dash line shows the value at 480.0 nm)
Is shown in FIG.

[0076]

[Table 6]

In Table 6, f ₀ = 66.34, F
_NO = 1.14, magnification = −0.1265.

[0078]

[Table 7]

[0079]

As is apparent from the above description, the projection lens of the present invention is composed of four lens groups of the first lens group to the fourth lens group in order from the projection surface side.
In a projection lens in which each of the first lens group to the third lens group has a positive refractive power and the fourth lens group has a negative refractive power, the first lens group and the third lens group have a plurality of acrylic lenses. The second lens group is formed of a spherical glass lens, and the fourth lens group is formed between an acrylic lens and a cathode ray tube face plate having a strong concave surface facing the projection surface and between the acrylic lens and the cathode ray tube face plate. It is characterized in that it is constituted by a cooling liquid filled in.

Therefore, in the projection lens of the present invention, only the second lens group is composed of the spherical glass lens and the other lens groups are composed of the acrylic lens, so that the wide angle of view and the aberration can be obtained. In particular, it is possible to obtain a projection lens in which color flare is appropriately corrected without increasing the production cost.

The specific shapes and structures shown in the above embodiments are merely examples of the implementation of the present invention, and the technical scope of the present invention is limited by these. Is not to be interpreted.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the projection lens of the present invention together with FIGS. 2 and 3, and this drawing is a schematic view showing the lens configuration.

FIG. 2 is a diagram showing a relative point aberration and a distortion aberration.

FIG. 3 is a diagram showing lateral aberration.

FIG. 4 shows a second embodiment of the projection lens of the present invention together with FIGS. 5 and 6, and this drawing is a schematic diagram showing the lens configuration.

FIG. 5 is a diagram showing a relative point aberration and a distortion aberration.

FIG. 6 is a diagram showing lateral aberration.

7 shows a third embodiment of the projection lens of the present invention together with FIG. 8 and FIG. 9, and this drawing is a schematic view showing the lens configuration.

FIG. 8 is a diagram showing a relative point aberration and a distortion aberration.

FIG. 9 is a diagram showing lateral aberration.

[Explanation of symbols]

 1 Projection Lens 1A Projection Lens 1B Projection Lens 2 CRT Face Plate 3 Coolant GR1 First Group Lens GR2 Second Group Lens GR3 Third Group Lens GR4 Fourth Group Lens L1 First Lens L3 Third Lens L5 Fifth Lens

Claims (8)

[Claims] 1. A first lens group to a fourth lens group in order from the projection surface side.
A projection lens configured by four lens groups of a lens group, wherein the first lens group to the third lens group each have a positive refracting power and the fourth lens group has a negative refracting power. The lens group and the third lens group are composed of a plurality of acrylic lenses, the second lens group is composed of a spherical glass lens, and the fourth lens group is composed of an acrylic lens having a strong concave surface on the projection surface side, a cathode ray tube face plate, and A projection lens comprising a cooling liquid filled between the acrylic lens and a cathode ray tube face plate. 2. In the first lens group, the first lens has a convex lens surface having a positive refracting power toward the projection surface when the lens surface shape is near the central portion, and is gradually negative as it goes from the central portion to the peripheral portion. F ₀ / f ₁ <0 where f ₀ is the focal length of the entire lens system and f ₁ is the focal length of the first lens group. .4 is satisfied, and ΔS _i is the amount of deviation of the lens surface S _{i from} the reference spherical surface, C
Is the paraxial curvature, Y is the distance from the optical axis, K is the conic coefficient, and A _j
(J = 4,6,8,10,12,14) is the 4th, 6th,
..., where the 14th-order aspherical coefficient, Σ is the sum for j, ΔS _i = C · Y ² / {1 + √ [1- (K + 1) C ² ·
Y ² ]} + Σ (A _j · Y ^j ) −C · Y ² / [1 + √ (1-C
² · Y ² )], the lens surface S on the projection surface side of the first lens
_2. The condition of 5 <ΔS ₂ −ΔS ₁ <13 is satisfied, where ΔS ₁ and ΔS ₂ are deviation amounts of the lens surface S ₂ on the _1st and cathode ray sides from the reference spherical surface, respectively. Projection lens. 3. In the third lens group, the lens surface shape of the fifth lens has a positive refractive power in the vicinity of the central portion, and gradually changes to a negative refractive power from the vicinity of the central portion toward the peripheral portion. Such an aspherical shape, ΔS _i is the amount of deviation of the lens surface S _{i from} the reference spherical surface, C is the paraxial curvature, Y is the distance from the optical axis, K is the conical coefficient, and A _j (j =
4,6,8,10,12,14) 4th, 6th, ...
, 14th-order aspherical coefficient, Σ is the sum of j, ΔS _i = C · Y ² / {1 + √ [1- (K + 1) C ² ·
Y ² ]} + Σ (A _j · Y ^j ) −C · Y ² / [1 + √ (1-C
² · Y ² )], the lens surface S on the projection surface side of the fifth lens
_{9. If} the deviation amounts of the lens surface S ₁₀ on the _9th and cathode ray sides from the reference spherical surface are ΔS ₉ and ΔS ₁₀ , respectively, the condition of 2.2 <ΔS ₁₀ −ΔS ₉ <4.0 is satisfied. Item 1. The projection lens according to item 1. 4. In the third lens group, the lens surface shape of the fifth lens has a positive refractive power in the vicinity of the central portion, and gradually changes to a negative refractive power from the central portion to the peripheral portion. Such an aspherical shape, ΔS _i is the amount of deviation of the lens surface S _{i from} the reference spherical surface, C is the paraxial curvature, Y is the distance from the optical axis, K is the conical coefficient, and A _j (j =
4,6,8,10,12,14) 4th, 6th, ...
, 14th-order aspherical coefficient, Σ is the sum of j, ΔS _i = C · Y ² / {1 + √ [1- (K + 1) C ² ·
Y ² ]} + Σ (A _j · Y ^j ) −C · Y ² / [1 + √ (1-C
² · Y ² )], the lens surface S on the projection surface side of the fifth lens
_9. The condition of 2.2 <ΔS ₁₀ −ΔS ₉ <4.0 is satisfied, where ΔS ₉ and ΔS ₁₀ are deviation amounts of ₉ and the lens surface S ₁₀ on the cathode ray side from the reference spherical surface. The projection lens described in 2. 5. The projection lens according to claim 1, wherein in the second lens group, the third lens satisfies the following conditions. ν _L3 > 55 where ν _L3 is the Abbe number of the third lens. 6. The projection lens according to claim 2, wherein in the second lens group, the third lens satisfies the following conditions. ν _L3 > 55 where ν _L3 is the Abbe number of the third lens. 7. The projection lens according to claim 3, wherein in the second lens group, the third lens satisfies the following conditions. ν _L3 > 55 where ν _L3 is the Abbe number of the third lens. 8. The projection lens according to claim 4, wherein in the second lens group, the third lens satisfies the following conditions. ν _L3 > 55 where ν _L3 is the Abbe number of the third lens.