JPH10186235A - Projection-use zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection-use zoom lens being reduced in the physical size and suppressing various aberrations associated with variable magnification and focusing. SOLUTION: A zoom lens 9 comprises group types of, from a screen side successively, a 1st lens group 10 with a negative refraction power, a 2nd lens group 20 with a positive refraction power, a 3rd lens group 30 with a positive refraction power, 4th lens group 40 with a negative refraction power, and 5th lens group 50 with a positive refraction power. The 1st lens group 10 comprises four lenses of, from a screen side successively, a positive lens 11 with both convex planes, a negative meniscus lens 12 with its convex plane facing the screen, a negative lens 13 with concave planes, and a positive meniscus lens 14 with its convex plane facing the screen. At the time of variable magnification, the 1st lens group 10 and the 5th lens group 50 are at fixed positions and the 2nd lens group 20, the 3rd lens group 30, and the 4th lens group 40 are moved. At the time of focusing, a position of a positive lens 14 included in the 1st lens group 10 and positioned most behind from the screen side is fixed and the remaining lenses 11-13 of the 1st lens group 10 are moved in one body in the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection zoom lens suitable for a projector for enlarging and projecting an image displayed on a film, a slide, or a liquid crystal display on a screen.

[0002]

2. Description of the Related Art In a projector for enlarging and projecting an image displayed on a film, a slide or a liquid crystal display on a screen, a telecentric type zoom lens is used as an optical system for projection. The projection zoom lens is configured to have a zoom ratio of about 1.4, and the mainstream is a two-group type, a three-group type, a four-group type, or a five-group type.

FIG. 16 shows a lens configuration of a conventional four-group type projection zoom lens. Zoom lens 1
Are, in order from the screen side, a first lens group 2 having a negative refractive power, a second lens group 3 having a positive refractive power, a third lens group 4 having a negative refractive power, and a fourth lens group 5 having a positive refractive power. Consists of The positions of the first lens group 2 and the fourth lens group 5 are fixed, and by moving the second lens group 3 to the screen side and moving the third lens group 4 to the object side, the wide-angle end to the telephoto end are moved. Zooming is performed on the side. In addition,
On the image plane side of the fourth lens group 5, a parallel glass 6 as a prism is arranged.

FIG. 21 shows a lens configuration of a conventional five-group type zoom lens for projection, in which the same reference numerals are used as those of the zoom lens 1 shown in FIG. The zoom lens 70 includes, in order from the screen side, a first lens group 71 having a negative refractive power, a second lens group 72 having a positive refractive power, a third lens group 73 having a positive refractive power, and a fourth lens group 73 having a negative refractive power. The lens unit 74 includes a fifth lens unit 75 having a positive refractive power.
On the image plane side of the fifth lens group 75, a parallel glass 76 as a prism is arranged. In the five-unit type zoom lens 70, when zooming from the wide-angle end to the telephoto end, the positions of the first lens group 71 and the fifth lens group 75 are fixed, and the second lens group 72, Third lens group 73,
And the fourth lens group 74 is relatively moved on the optical axis.

In both the four-group type zoom lens 1 and the five-group type zoom lens 70, when performing focus adjustment, the first lens groups 2 and 71 located closest to the screen are integrated. It is common to move on the optical axis.

[0006]

However, in the conventional zoom lens constructed as described above, the curvature of field is generally large and the effective image circle is small. However, there is a problem in that if the total length of the lens system is forcibly shortened, variations in various aberrations increase and cannot be suppressed. Further, in the conventional zoom lens, chromatic aberration of magnification due to zooming varies greatly, and it is difficult to maintain a good balance of various aberrations over the entire focal range. Furthermore, since the curvature of field greatly fluctuates even during focusing, there is a problem that the effective image circle becomes small and the focus adjustment range cannot be set wide.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has as its object to provide a projection zoom lens which is reduced in size and suppresses fluctuations of various aberrations accompanying zooming and focusing. I do.

[0008]

In order to achieve the above object, a zoom lens according to the present invention comprises, in order from the screen side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power,
The fifth lens unit has a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end. When doing, the first
The lens group and the fifth lens group are fixed, the second lens group, the third lens group, and the fourth lens group are moved to the screen side, and the focal lengths of the entire lens system at the wide-angle end and the telephoto end are respectively set. Assuming that f _W , f _T , the focal length of the second lens group is f ₂ , and the total length of the lens system is L, 1.80 <L / f _T <2.18 92 <L / (f _T / f _W ) <125 0.7 <f ₂ / f _T <1.1

Further, when performing focus adjustment, a lens located at the rearmost position from the screen side among the lenses constituting the first lens group is fixed, and lenses other than the rearmost lens of the first lens group are fixed. Is preferably moved integrally on the optical axis. The first lens group is arranged in order from the screen side.
A positive lens with both convex surfaces, a meniscus-shaped negative lens with the convex surface facing the screen, and a negative lens with both concave surfaces,
It is preferable to constitute four lenses including a meniscus positive lens whose convex surface faces the screen.

The first lens group includes a positive lens having both convex surfaces, a meniscus-shaped positive lens having the convex surface facing the screen, and a negative lens having both concave surfaces, and a second lens group. A meniscus-shaped positive lens with the convex surface facing the screen may be used. In addition, the third
The lens group includes at least one compound lens formed by joining a positive lens having both convex surfaces and a negative meniscus lens having a concave surface facing the screen, and the fourth lens group includes a compound lens having both convex surfaces. And a negative lens having concave surfaces on both sides.

Still further, the fifth lens group may include a screen.
In order from the side, the negative lens with concave surfaces on both sides and the positive lens with convex surfaces on both sides.
Lens with a lens and a concave screen
Meniscus-shaped positive lens directed toward
And the fourth lens group constituting the fifth lens group.
Let the Abbe number of each lens be ν₅₁, Ν₅₂, Ν₅₃, Ν ₅₄
35 <ν₅₂−ν₅₁<48 69 <ν₅₁+ Ν₅₃+ Ν₅₄It is preferable to satisfy each condition of <109.

[0012]

In the present invention, the zoom lens is constructed in a five-group form, and the positions of the first lens group and the fifth lens group are fixed, while the second lens group, the third lens group, and the fourth lens group are fixed. Is relatively moved to change the projection magnification, a large magnification can be obtained while shortening the overall length of the lens system. By satisfying the following condition: 1.80 <L / f _T <2.18 92 <L / (f _T / f _W ) <125, the variation in field curvature due to zooming is suppressed, and the balance of various aberrations is reduced. Can be kept in a good state. If at least one of the conditional expressions is below the lower limit, the refractive power of each lens group becomes too strong, and the fluctuation of various aberrations becomes large, and it becomes difficult to keep these in a well-balanced manner. If at least one of the above conditional expressions exceeds the upper limit, each lens group will not have a sufficient refractive power, so that obtaining a desired magnification will increase the overall length of the lens system.

Further, by satisfying conditional expression 0.7 <f ₂ / f _T <1.1, it is possible to increase the magnification without extending the entire length of the lens system. If the lower limit of the conditional expression is exceeded, the positive refracting power of the second lens group becomes too strong, so that the deterioration of the curvature of field cannot be suppressed and the distortion increases.
On the other hand, when the value exceeds the upper limit, the refractive power of the second lens group becomes weak, so that it becomes difficult to obtain a sufficient magnification.

The third lens group has at least one compound lens formed by joining a positive lens having both convex surfaces and a negative meniscus lens having a concave surface facing the screen. By constituting the lens group from a positive lens with convex surfaces on both sides and a negative lens with concave surfaces on both sides,
Coma can be corrected well.

The fifth lens group includes a compound lens formed by joining a negative lens having concave surfaces on both sides and a positive lens having convex surfaces on both sides; a meniscus-shaped positive lens having a concave surface facing the screen; By forming a positive lens having a convex surface and satisfying the following conditional expression: 35 <ν ₅₂ −ν ₅₁ <48 (a) 69 <ν ₅₁ + ν ₅₃ + ν ₅₄ <109 (b) In addition, it is possible to suppress fluctuations in chromatic aberration of magnification due to zooming, maintain a balance of various aberrations, and obtain good optical performance. When the lower limit of conditional expression (a) or the upper limit of conditional expression (b) is exceeded, chromatic aberration of magnification increases,
It becomes difficult to keep the balance of various aberrations. If the upper limit of conditional expression (a) or the lower limit of conditional expression (b) is exceeded, when relatively inexpensive glass material is used as a lens molding material, chromatic aberration is too deteriorated to be suppressed and correction is made. Can not be done.

Further, when performing the focus adjustment, the lens located at the rearmost position from the screen side among the lenses constituting the first lens group is fixed, and the lenses other than the rearmost lens in the first lens group are fixed. By moving the lens integrally on the optical axis, the focal position can be changed by only slightly moving the lens, and fluctuations of various aberrations due to focusing can be suppressed. . In particular, the first lens group includes, in order from the screen side, a positive lens having both convex surfaces, a negative meniscus lens having a convex surface facing the screen, a negative lens having a concave surface both surfaces, and a meniscus having a convex surface facing the screen. With the configuration of four lenses including a positive lens having a shape, the combined focal length of the first lens group can be shortened, and the amount of movement of the lens during focusing can be further reduced.

The first lens group includes three lenses: a positive lens having both convex surfaces, a positive meniscus lens having the convex surface facing the screen, and a negative lens having both concave surfaces. A meniscus-shaped positive lens having a convex surface facing the screen may be used as the second lens group. According to this, fluctuations of various aberrations due to zooming and focusing can be suppressed with a small number of lenses, and a good balance between them can be maintained.

[0018]

FIG. 1 shows a configuration of a zoom lens according to the present invention. The zoom lens 9 includes, in order from the screen side, a first lens group 10 having a negative refractive power, a second lens group 20 having a positive refractive power, and a third lens group 3 having a positive refractive power.
0, fourth lens group 40 with negative refractive power, fifth lens group with positive refractive power
The lens group 50 has a five-group format. An aperture SP is provided on the screen side of the third lens group 30, and a parallel glass 60 as a prism is provided on the object side of the fifth lens group 50.
Is arranged.

The first lens group 10 includes, in order from the screen side, a positive lens 11 having both convex surfaces, a meniscus-shaped negative lens 12 having a convex surface facing the screen, and a negative lens 13 having both concave surfaces. The second lens group 20 includes a single meniscus positive lens 21 with the convex surface facing the screen. The third lens group 30 is composed of a compound lens 33 in which a positive lens 31 having both convex surfaces and a negative meniscus lens 32 having a concave surface facing the screen are joined.
The fourth lens group 40 includes a positive lens 41 having convex surfaces on both sides, and a negative lens 42 having concave surfaces on both sides. The fifth lens group 50 includes, in order from the screen side, a compound lens 55 formed by joining a negative lens 51 having concave surfaces on both sides and a positive lens 52 having convex surfaces on both sides, and a meniscus-shaped positive lens having the concave surface facing the screen side. 53 and a positive lens 54 having convex surfaces on both sides.

When zooming from the wide-angle end to the telephoto end, the positions of the first lens group 10 and the fifth lens group 50 are fixed, and the second lens group 20 and the third lens group are fixed. 30 and the fourth lens group 40 are moved to the screen side. The stop SP is moved integrally with the third lens group 30.

[0021]

【Example】

"First Embodiment" The specifications of the zoom lens 9 are as follows. _{f = 45.2mm~58.6mm f 2 = 54.5mm L} = 119.87mm F NO = 2.5~ 3.0 m = 1.3

In the above data, f is the focal length of the entire optical system, f ₂ is the focal length of the second lens group 20, L is the total length of the lens system, F _NO is the F number, and m is the zoom ratio. I have.

The lens data of the first embodiment is shown in Table 1 below.
Shown in The surface number i is a number given to the surface of each lens in order from the screen side, and the surface interval D represents the lens thickness or the air space between the next surface (unit: mm).

[0024]

[Table 1]

The focal length f is 45.2 mm, 51.
When the distances are 5 mm and 58.6 mm, the surface distance D6 between the first lens group 10 and the second lens group 20, the surface distance D8 between the second lens group 20 and the stop SP, the third lens group 30 and the fourth lens group The surface distance D13 between the first lens group 40 and the surface distance D17 between the fourth lens group 40 and the fifth lens group 50 changes as shown in Table 2 below.

[0026]

[Table 2]

Further, the focal length at the wide-angle end is represented by f _W ,
And the focal length at the telephoto end and f _T, which is a characteristic value of the zoom lens, "L / f _T", "L / (f _T /
f _W ) ”and“ f ₂ / f _T ”are L / f _T = 119.87 / 58.6６2.05 L / (f _T / f _W ) = 1119.87 / (58 .6 / 45.2) ≒ 92.21 f ₂ / f _T = 54.5 / 58.6 ≒ 0.93, and the conditional expression 1.80 <L / f _T <2.18 92 <L / ( f _T / f _W ) <125 0.7 <f ₂ / f _T <1.1.

The Abbe numbers of the four lenses 51 to 54 constituting the fifth lens group 50 are denoted by ν ₅₁ , ν ₅₂ and ν, respectively.
₅₃ and ν ₅₄ , the respective values of “ν ₅₂ −ν ₅₁ ” and “ν ₅₁ + ν ₅₃ + ν ₅₄ ”, which are the characteristic values of the fifth lens group 50, are ν ₅₂ −ν ₅₁ = 70.4 −23.8 = 46.6 ν ₅₁ + ν ₅₃ + ν ₅₄ = 23.8 + 23.8 + 23.8
= 71.4, thereby satisfying the following condition: 35 <ν ₅₂ −ν ₅₁ <4869 <ν ₅₁ + ν ₅₃ + ν ₅₄ <109.

FIGS. 2 and 3 show aberration diagrams at the wide-angle end of the zoom lens of the first embodiment, and FIGS. 4 and 5 show aberration diagrams at the telephoto end. 2 and 4, (A) shows spherical aberration, (B) shows astigmatism,
(C) represents distortion. In the spherical aberration diagrams of FIG. 2 and FIG. 4A, reference numerals a, e, F, and g denote light of 610.0 nm, e-line (546.1 nm),
The aberrations with respect to the F line (486.1 nm) and the g line (435.8 nm) are shown.
T represents aberrations with respect to the spherical and meridional image planes, respectively. FIGS. 3 and 5 are transverse aberration diagrams. In the figures, (A), (B), (C), (D), and (E) show image height ratios (1.00), (0. 90), (0.70),
The aberrations at (0.50) and (0.00) are shown.

For comparison, FIG. 1 shows aberration diagrams at the wide-angle end of the conventional four-group zoom lens shown in FIG.
7 and 18 and aberration diagrams at the telephoto end are shown in FIGS.
And FIG.

[Second Embodiment] FIG. 6 shows a second embodiment of the configuration of the zoom lens.
Used in common with the first embodiment shown in FIG. The specifications of the zoom lens according to the second embodiment are as follows.

F = 50.6 mm to 74.0 mm f ₂ = 68.0 mm L = 148.00 mm F _NO = 2.8 to 3.6 m = 1.5

Table 3 shows lens data of the second embodiment.

[0034]

[Table 3]

The focal length f is set to 50.6 mm, 63.
When the distances are 2 mm and 74.0 mm, the surface distance D6 between the first lens group 10 and the second lens group 20, the surface distance D8 between the second lens group 20 and the stop SP, the third lens group 30, and the fourth lens group The distance D13 between the first lens group 40 and the distance D17 between the fourth lens group 40 and the fifth lens group 50 varies as shown in Table 4 below.

[0036]

[Table 4]

The characteristic value of the zoom lens of the second embodiment is as follows: L / f _T = 148.00 / 74.0７４2.00 L / (f _T / f _W ) = 148.00 / (74.0 / 50.6) ≒ 101.37 f ₂ / f _T = 68.0 / 74.0 ≒ 0.92 ν ₅₂ −ν ₅₁ = 70.4−23.8 = 46.6 ν ₅₁ + ν ₅₃ + ν ₅₄ = 23 .8 + 23.8 + 23.8 = 71.4, and the conditional expression 1.80 <L / f _T <2.18 92 <L / (f _T / f _W ) <125 0.7 <f ₂ / f _T < 1.1 35 <ν ₅₂ −ν ₅₁ <48 69 <ν ₅₁ + ν ₅₃ + ν ₅₄ <109.

FIGS. 7 and 8 show aberration diagrams at the wide-angle end of the zoom lens according to the second embodiment, and FIGS. 9 and 10 show aberration diagrams at the telephoto end.

[Third Embodiment] FIG. 11 shows a third embodiment of the configuration of the zoom lens.
Used in common with the first embodiment shown in FIG. In the zoom lens of the third embodiment, the first lens group 10 includes, in order from the screen side, a positive lens 11 having convex surfaces on both sides, a negative meniscus lens 12 having a convex surface facing the screen side, and a concave lens having both surfaces concave. It comprises four lenses: a negative lens 13 and a positive meniscus lens 14 with the convex surface facing the screen.

When zooming from the wide-angle end to the telephoto end, the positions of the first lens group 10 and the fifth lens group 50 are fixed, and the second lens group 20 and the third lens group are fixed. 30 and the fourth lens group 40 are moved to the screen side. The stop SP is moved integrally with the second lens group 20. When performing focus adjustment, the meniscus-shaped positive lens 14 located at the rearmost position from the screen side among the four lenses 11 to 14 constituting the first lens group 10 is used.
Are fixed, the remaining lenses 11 to 13 of the first lens group 10 are integrally moved on the optical axis.

The specifications of the zoom lens of the third embodiment are as follows.

F = 47.5 mm to 76.1 mm f ₂ = 78.78 mm L = 162.94 mm to 164.92 mm F _NO = 2.5 to 3.2 m = 1.6 Bf = 49.2 mm

In the above data, Bf indicates the back focus. Table 5 shows lens data of the third example.

[0044]

[Table 5]

The focal length f is 47.5 mm, and the focal length f is 61.5 mm.
8 mm and 76.1 mm, the surface distance D8 between the first lens group 10 and the second lens group 20, the surface distance D11 between the stop SP and the third lens group 30, the third lens group 30 and the fourth lens group And the fourth lens group 40
The surface distance D19 between the lens and the fifth lens group 50 changes as shown in Table 6 below.

[0046]

[Table 6]

Further, the projection distance is set to infinity, 3.6 m,
When focus adjustment is performed at 1.4 m, the first lens group 1
The surface distance D6 between the negative lens 13 and the positive lens 14 in 0 is
It changes as shown in Table 7 below.

[0048]

[Table 7]

The characteristic value of the zoom lens of the third embodiment is as follows: L _min / f _T = 162.94 / 76.1．2.14 L _max / f _T = 164.92 / 76.1 ≒ 2.17 L _{min / (f T / f W} ) = 162.94 / (76.1 / 47.5) ≒ 101.70 L max / (f T / f W) = 164.92 / (76.1 / 47.5 ) ≒ 102.94 f ₂ / f _T = 78.78 / 76.1 ≒ 1.03 ν ₅₂ −ν ₅₁ = 70.4−23.8 = 46.6 ν ₅₁ + ν ₅₃ + ν ₅₄ = 23.8 + 42. 3 + 23.8 = 89.9, and the conditional expression 1.80 <L / f _T <2.18 92 <L / (f _T / f _W ) <125 0.7 <f ₂ / f _T <1.1 35 <ν ₅₂ −ν ₅₁ <48 69 <ν ₅₁ + ν ₅₃ + ν ₅₄ <109.

FIGS. 12 and 13 show aberration diagrams of the zoom lens according to the third embodiment at a projection distance of 3.6 m at the wide-angle end.
FIG. 1 shows aberration diagrams at a projection distance of 1.4 m at the wide-angle end.
4 and FIG. In the spherical aberration diagrams of FIG. 12A and FIG. 14A, symbols C, e, F, and g are C line (656.3 nm) and e line (546.1n), respectively.
m), F line (486.1 nm), g line (435.8 n)
m).

[0051]

As described above, according to the present invention, the zoom lens is constituted by a five-unit type, and at the time of zooming, the positions of the first lens unit and the fifth lens unit are fixed.
By relatively moving the second lens group, the third lens group, and the fourth lens group, a large magnification can be obtained while shortening the overall length of the lens system. Moreover, by adjusting the ratio between the total length of the lens system and the zoom ratio, it is possible to suppress fluctuations in the field curvature.

The third lens group has at least one compound lens formed by joining a positive lens having both convex surfaces and a negative meniscus lens having a concave surface facing the screen. By composing the lens group with a positive lens having both convex surfaces and a negative lens having both concave surfaces, coma can be satisfactorily corrected. further,
By adjusting the Abbe number of each lens constituting the fifth lens group, fluctuations in chromatic aberration of magnification due to zooming are suppressed and the balance of various aberrations is maintained in a good state regardless of the type of lens molding material. be able to.

Further, at the time of performing the focus adjustment, the lens located at the rearmost position from the screen side in the first lens group is fixed, and the remaining lenses are moved integrally, so that a slight The focal position can be changed by moving the lens, and fluctuations of various aberrations due to focusing can be suppressed. Further, the first lens group includes, in order from the screen side, a positive lens having both convex surfaces, a meniscus-shaped negative lens having a convex surface facing the screen, a negative lens having both concave surfaces, and a meniscus having a convex surface facing the screen. The first lens is constituted by four lenses including a positive lens having
The combined focal length of the lens groups can be shortened, and the amount of movement of the lens during focusing can be further reduced.

The first lens group is composed of a positive lens having both convex surfaces, a meniscus-shaped positive lens having the convex surface facing the screen, and a negative lens having both concave surfaces. By using a meniscus-shaped positive lens with the convex surface facing the screen side, fluctuations in various aberrations due to zooming and focusing can be suppressed with a small number of lenses.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram showing a first embodiment of a zoom lens according to the present invention.

2A and 2B are aberration diagrams at the wide-angle end of the zoom lens shown in FIG. 1, wherein FIG. 2A shows spherical aberration, FIG. 2B shows astigmatism, and FIG. 2C shows distortion.

3A and 3B are lateral aberration diagrams at the wide-angle end of the zoom lens shown in FIG. 1; FIG. 3A shows aberration at an image height ratio of 1.00; FIG. 3B shows aberration at an image height ratio of 0.90; C) shows aberration at an image height ratio of 0.70, and (D) shows aberration at an image height ratio of 0.5.
And (E) represents aberration at an image height ratio of 0.00.

4A and 4B are aberration diagrams at the telephoto end of the zoom lens shown in FIG. 1, wherein FIG. 4A shows spherical aberration, FIG. 4B shows astigmatism, and FIG. 4C shows distortion.

5A and 5B are lateral aberration diagrams at the telephoto end of the zoom lens shown in FIG. 1, wherein FIG. 5A shows aberration at an image height ratio of 1.00, FIG. C) shows aberration at an image height ratio of 0.70, and (D) shows aberration at an image height ratio of 0.5.
And (E) represents aberration at an image height ratio of 0.00.

FIG. 6 is a lens configuration diagram showing a second embodiment of the zoom lens according to the present invention.

7 is an aberration diagram at a wide-angle end of the zoom lens shown in FIG.

8 is a lateral aberration diagram at the wide-angle end of the zoom lens shown in FIG.

9 is an aberration diagram at a telephoto end of the zoom lens shown in FIG.

10 is a lateral aberration diagram at the telephoto end of the zoom lens shown in FIG.

FIG. 11 is a lens configuration diagram showing a third embodiment of the zoom lens according to the present invention.

12 is an aberration diagram at a projection distance of 3.6 m at the wide-angle end of the zoom lens shown in FIG.

13 is a lateral aberration diagram at a projection distance of 3.6 m at the wide-angle end of the zoom lens shown in FIG.

14 is an aberration diagram at a projection distance of 1.4 m at the wide-angle end of the zoom lens shown in FIG.

15 is a lateral aberration diagram at a projection distance of 1.4 m at the wide-angle end of the zoom lens shown in FIG.

FIG. 16 is a lens configuration diagram showing a conventional four-group type zoom lens.

17 is an aberration diagram at a wide-angle end of the zoom lens shown in FIG.

18 is a lateral aberration diagram at the wide-angle end of the zoom lens shown in FIG.

19 is an aberration diagram at a telephoto end of the zoom lens shown in FIG.

20 is a lateral aberration diagram at the telephoto end of the zoom lens shown in FIG.

FIG. 21 is a lens configuration diagram showing a conventional five-group type zoom lens.

[Explanation of symbols]

 1, 9, 70 Zoom lens 2, 10, 71 First lens group 3, 20, 72 Second lens group 4, 30, 73 Third lens group 5, 40, 74 Fourth lens group 50, 75 Fifth lens group 33,55 compound lens

Claims (6)

[Claims] A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, The first lens group and the fifth lens group are fixed when performing zooming from the wide-angle end side to the telephoto end side. the second lens group, the third lens group, and the fourth lens group is moved to the screen side, the focal length of the entire lens system, respectively f _W at the wide-angle end and the telephoto end, f _T, the focal length of the second lens group Where f _{2 is} the length of the lens system and L is 1.80 <L / f _T <2.18 92 <L / (f _T / f _W ) <125 0.7 <f ₂ / f _T < 1.1 A zoom lens for projection, characterized by satisfying the following conditions: 2. When performing focus adjustment, a lens located at the rearmost position from the screen side among the lenses constituting the first lens group is fixed, and a lens other than the last lens in the first lens group is fixed. 2. The projection zoom lens according to claim 1, wherein said lens is integrally moved on the optical axis. 3. The first lens group includes, in order from the screen side, a positive lens with convex surfaces on both sides, a meniscus-shaped negative lens with the convex surface facing the screen side, a negative lens with concave surfaces on both sides, and a convex lens on the screen. 3. The projection zoom lens according to claim 2, comprising four lenses including a meniscus-shaped positive lens directed to the side. 4. The first lens group includes, in order from the screen side, a positive lens having both convex surfaces, a meniscus-shaped negative lens having a convex surface facing the screen, and a negative lens having both concave surfaces. 3. The projection zoom lens according to claim 1, wherein the second lens group comprises a positive meniscus lens having a convex surface facing the screen. 5. The third lens group includes at least one compound lens formed by joining a positive lens having both convex surfaces and a negative meniscus lens having a concave surface facing the screen, and the fourth lens group. 2. The group comprises a positive lens having convex surfaces on both sides and a negative lens having concave surfaces on both sides.
5. The projection zoom lens according to any one of items 4 to 4. 6. The fifth lens group includes, in order from the screen side, a compound lens formed by joining a negative lens with concave surfaces on both sides and a positive lens with convex surfaces on both sides, and a meniscus-shaped concave surface with the concave surface facing the screen. When the Abbe number of each of the four lenses constituting the fifth lens group is ν ₅₁ , ν ₅₂ , ν ₅₃ , and ν ₅₄ , the lens is composed of a positive lens and a positive lens having convex surfaces on both sides. 6. A lens according to claim 1, wherein the following condition is satisfied: <ν ₅₂ −ν ₅₁ <48 69 <ν ₅₁ + ν ₅₃ + ν ₅₄ <109.
The projection zoom lens described.