JPH08313810A - Projection zoom lens - Google Patents

Abstract

PURPOSE: To provide a projection zoos lens for realizing a projection device such as a small OHP provided with enlarging function. CONSTITUTION: A projection zoom lens 10 is composed, in order from the screen side, of a focus adjusting lens group G1 of negative refractive power, a power varying lens group G2 of positive refractive power and a compensating lens group G3 of negative refractive power. Even when the power varying lens group G2 is moved on the optical axis for varying the power, since the optical distance between the focus adjusting lens group G1 and a surface 2 to be projected is kept constant by the compensating lens group G3, a sharp and enlarged image is projected on a screen 5. Consequently, since the surface 2 to be projected remains immobile, the reduction of the size and the weight of the projection device is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection device having a condensing optical system, such as an overhead projector (OH).
P) and a zoom lens for projection suitable for a liquid crystal projector.

[0002]

2. Description of the Related Art In an apparatus for projecting or projecting an image formed on a projection surface such as an OHP, there is a method of adding a magnifying lens to a projection lens as a method of enlarging a part or the whole of the image. However, since the magnification obtained with a magnifying lens is determined for each lens, it is necessary to prepare many lenses in order to obtain a desired magnifying power. Furthermore, each lens must be replaced. I won't. In addition, since the focal length changes by adding a magnifying lens, it is necessary to move the projection lens accordingly to adjust the focus, or to adjust the distance between the projection surface and the projection lens. .

In Japanese Patent Laid-Open No. 61-158309, a lens having a constitution in which a second group of lenses is used and the enlargement ratio can be continuously changed is adopted. Further, the distance between this lens and a projection object is changed. A projection device is described. This projection device can easily obtain a desired magnification and can prevent the decrease in illuminance due to enlargement to some extent. However, in addition to the mechanism for moving the lens at the time of zooming, a mechanism for accurately moving the projection target is required, which complicates the entire mechanism of the projection apparatus. Therefore, the projection device becomes large, heavy, and expensive. Furthermore, since the projection object is moved, the entire projection object cannot be enlarged and projected on the screen.

[0004]

In recent years, downsizing, weight reduction, and cost reduction have also been considered in projection devices such as OHPs and liquid crystal projectors, and a scaling means suitable for this is required. There is. Therefore, an object of the present invention is to provide a projection zoom lens suitable for such a projection device. That is, it is an object of the present invention to provide a compact zoom lens for projection with a simple structure. Another object of the present invention is to provide a zoom lens for projection that can eliminate the complicated mechanism for moving the projection surface according to the magnification change and can reduce the size and cost of the entire projection apparatus. It is another object of the present invention to provide a compact and high-magnification projection zoom lens.

[0005]

In the present invention, a zoom lens is constructed by three lens groups. That is, the zoom lens of the present invention is a projection zoom lens for projecting an image incident from the condensing optical system onto a screen, and in order from the screen side, focus adjustment of a negative refractive power whose position is fixed during zooming. Lens group for zooming, a lens group for zooming with a positive refractive power that moves in the optical axis direction for zooming, and a lens group for focus adjustment and the optical distance to keep the optical distance constant between the images. And a lens group for correcting the negative refractive power that moves in the axial direction.

[0006]

In such a projection zoom lens according to the present invention, even if the lens group for zooming moves during zooming and the focal length changes, the lens group for correction and the lens group for focus adjustment are used for projection. The optical distance from the image that is the object of can be kept constant. Therefore, a magnified and clear image can be displayed on the screen without moving either the lens group for focus adjustment or the image. Therefore, the projection apparatus using the projection zoom lens of the present invention does not require a mechanism for moving the entire projection zoom lens or moving the image side such as the projection surface or the condensing optical system side. The whole mechanism is simple. Therefore, the projection apparatus can be made compact, lightweight and low cost.
In addition, since the focus adjustment lens group located closest to the screen does not have to be moved due to zooming, a mirror or prism may be placed in the projection direction to reduce the installation space, etc. Etc. can be reduced.

Further, since a simple structure of three lens groups is sufficient, the entire zoom lens can be compactly assembled and can be provided at a low cost.

Further, by making the imaging magnification β _W at the wide-angle end and the imaging magnification β _T at the telephoto end of the zoom lens group satisfy the following expression (1), a more compact zoom lens can be realized. .

| Β _W | <1 <| β _T | (1) where β _W and β _T are image forming magnifications in a reduction optical system in which the screen is the object plane and the projected surface is the image plane. Is.

By setting the imaging magnification of the lens group for zooming to satisfy the expression (1), the moving distance of the lens group for correction becomes small, so that the entire zoom lens for projection accompanying zooming The moving distance can be minimized, and the projection zoom lens can be compactly assembled. Also, since the difference between the size of the projection zoom lens at the wide-angle end and the size at the telephoto end is minimized, the installation space for the projection zoom lens in the projection device can be small, and the projection device can be made smaller. it can. Furthermore, since the difference in back focus between the wide-angle end and the telephoto end is small, a sufficient projection range can be secured even at the wide-angle end, and the lens group, especially the correction lens group, can be downsized.

Further, the zoom lens group is made up of two lens groups, a first lens group having a positive refractive power and a second lens group having a positive refractive power in order from the screen side. 1
It is also effective to move the second lens group in the optical axis direction so as to increase the air gap. By using the above-described two-lens configuration for the variable power lens group, it is possible to reduce the moving distance of the variable power lens group when obtaining high magnification, and
It is also possible to prevent deterioration of various aberrations due to the shortened focal length. Therefore, it is possible to provide a high-magnification projection zoom lens having a short overall length, a compact size, and good aberrations.

[0012]

【Example】

Example 1 FIG. 1 shows a projection zoom lens 10 according to Example 1 of the present invention and an optical system of an overhead projector (OHP) using the same. OH illustrated
In the P optical system, light from a light source (not shown) is condensed by the condensing optical system 3 including the Fresnel lens 1 onto the projection zoom lens 10 through the projected image 2.

The light spatially modulated by the projected image 2 is projected on the screen 5 through the projection zoom lens 10. The projection zoom lens 10 of this example is a projection lens capable of projecting a magnified image on the screen 5. In FIG. 1, the telephoto end (a) is the standard state and the wide-angle end (c) is the enlarged state. Also, the position of each lens in the intermediate state (b) is shown.

The projection zoom lens 10 of this example is composed of seven lenses L1 to L7 which are grouped into three lens groups G1 to G3 from the screen 5 side, and detailed data of each lens will be described below. As shown in. The lens group G1 closest to the screen 5 is a focus adjustment lens group having a negative refractive power, and is a negative meniscus lens L convex toward the screen side in order from the screen side.
1 and a positive meniscus lens L2 having a convex surface on the screen side. The position of the lens group G1 for focus adjustment is not moved during zooming, and once the focus has been adjusted and the distance W1 with the screen 5 is determined, thereafter the lens group for zooming and the lens for correction are used. By moving the group, you can get a sharp or magnified image on the screen.

Located in the middle of the projection zoom lens 10 is a lens group G2 for zooming, and in this example, a positive lens L having a convex shape on the screen side in order from the screen side.
3, a negative meniscus lens L4 having a concave surface on the screen side, a negative meniscus lens L5 having a convex surface on the screen side, and a positive lens L6 having a convex surface on the condenser optical system side. This zoom lens group G2 moves from the position at the telephoto end to the position at the wide-angle end on the optical axis from the screen side toward the condensing optical system side, and a projection image with a predetermined magnification is projected on the screen. Can be obtained. In the projection zoom lens of this example, the lenses L1 to L7 have negative refracting power,
It is a combination of positive, positive, negative, negative, positive, negative, and the focus position by the condensing optical system can be set to a position close to the lens group G1 for focus adjustment. Therefore, the light projected from the projection zoom lens of this example has a small area in the vicinity of the projection zoom lens. Therefore, in the projection device in which the mirror and the prism are installed in the projection direction, the size of the mirror and the like can be further reduced.

A lens group G3 for correction is arranged on the side of the projection zoom lens 10 closest to the condensing optical system 3.
The correcting lens group G3 of this example is composed of a negative lens L7 having concave surfaces on both sides. The correction lens group G3 moves on the optical axis so that the optical distance between the focus adjustment lens group G1 and the projection surface 2 does not change even if the magnification changing lens group G2 moves. By providing such a correction lens group G3, a clear projection image can be obtained on the screen 5 without changing the distance between the focus adjustment lens group G1 and the projection surface 2 even if the magnification is changed. You can Therefore, a mechanism for moving the projection surface 2 or the like is not necessary, and an image obtained by enlarging the projection surface 2 as a whole and projecting it can be easily obtained.

Further, the zoom lens group G2 of this example is
The imaging magnification β _W of the reduction optical system at the wide-angle end and the imaging magnification β _T of the reduction optical system at the telephoto end are selected so as to satisfy the following equation.

| Β _W | <1 <| β _T | (1) Therefore, as shown in FIG. 1, the lens group G3 for correction has the most screen near the intermediate state (FIG. 1 (b)). On the optical axis so as to be located on the side of the lens, and the position at the telephoto end (FIG. 1A) and the position at the wide-angle end (FIG.
There is almost no difference from (c)). Therefore, the total length of the projection zoom lens 10 of this example is short, and the entire zoom lens can be compactly assembled. Also, since the difference in back focus between the telephoto end and the wide-angle end is small,
A sufficient projected range can be obtained without increasing the diameter of the lens group G3 for correction. Therefore, the projection zoom lens 1
It is also effective to obtain a projection image in which the entire projection surface is enlarged.

In the lens data shown below, r ₁ to
r ₁₄ is the radius of curvature of each lens surface arranged in order from the screen side, d _{1 to} d ₁₃ are the distances between the lens surfaces arranged in order from the screen side, and n _{1 to} n ₇ are arranged in order from the object side. The refractive index (d line) of each lens, and ν _{1 to} ν ₇ are the Abbe numbers (d line) of the lenses arranged in order from the object side.

Lens data r ₁ = 138.688 d ₁ = 2.500 n ₁ = 1.78590 ν ₁ = 44.19 r ₂ = 39.558 d ₂ = 5.700 r ₃ = 41.553 d ₃ = 4.850 n ₂ = 1.80518 ν ₂ = 25.43 r ₄ = 61.154 d _{4 = 8.057~ 34.596 r 5 = 63.745} d 5 = 6.050 n 3 = 1.78800 ν 3 = 47.38 r 6 = -501.932 d 6 = 4.650 r 7 = -61.774 d 7 = 2.500 n 4 = 1.84666 ν 4 = 23.78 r 8 = _{-112.465 d 8 = 2.600 r 9 =} 190.193 d 9 = 2.500 n 5 = 1.84666 ν 5 = 23.78 r 10 = 66.212 d 10 = 5.540 r 11 = -960.801 d 11 = 7.500 n 6 = 1.80440 ν 6 = 39.58 r 12 = _{-60.778 d 12 = 26.484~ 1.013 r 13} = -235.524 d 13 = 3.000 n 7 = 1.48749 ν 7 = 70.21 r 14 = 235.524 projection distance W1 1900 mm between the object-image distance W2 2324.1Mm focal length standard (telephoto end) 309. 34mm Magnification (wide-angle end) 245.68mm Imaging magnification Standard (telephoto end) -0.190 Large (wide angle end) -0.140 imaging magnification standard (telephoto end) magnification 1.357 zooming lens group G2 β _T -1.144 expansion (wide angle end) β _W -0.8431 condensing optical system Focusing position of 379 mm (distance from the projection surface to the screen side) FIGS. 2 and 3 show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of this example, respectively. . 4 and 5 show lateral aberration diagrams of the projection zoom lens of this example, respectively. In the astigmatism diagram and the lateral aberration diagram, the tangential ray (T) and the sagittal ray (S) are shown, and in the spherical aberration diagram and the lateral aberration diagram, the d-line (587.
6 nm), g-line (435.8 nm) and C-line (65
(6.3 nm) is shown. The numerical aperture (NA) is 0.023. The aberration diagrams of the present embodiment and the following embodiments are shown by a reduction optical system in which the screen is the object plane and the projected surface is the image plane.

The magnifying power of the projection zoom lens of this example is 1.
357, and the illuminance is reduced to about 54% due to the enlargement. When obtaining a projected image on the screen, a decrease in illuminance of up to about 50% is within an acceptable range, and it is considered that a mechanism for correcting the illuminance is unnecessary. In addition, it is also possible to add a function of increasing the light intensity of the light source in accordance with the movement of the projection zoom lens to the projection apparatus in order to compensate for the decrease in illuminance due to the enlargement. Also, the magnification of the projection zoom lens of this example is a value suitable for enlarging the entire image on the projection surface, and it is possible to enlarge almost the entire image within the tolerance range of a normal screen or mirror. The projected image is obtained.

[Embodiment 2] FIG. 6 shows a projection zoom lens 10 according to Embodiment 2 of the present invention and an OHP optical system using the same. FIG. 6A shows the lens position at the telephoto end in the standard state, FIG. 6B shows the intermediate position, and FIG. 6C shows the lens position at the wide-angle end in the enlarged state. It is shown. Also in this example, the condensing optical system 3 using the Fresnel lens 1 is adopted, and the common portions are denoted by the same reference numerals and the description thereof will be omitted. The projection zoom lens 10 of this example is also composed of seven lenses L1 to L7 which are grouped into three lens groups G1 to G3 from the screen 5 side, and detailed data of each lens is shown below. There is a street. The lens group G1 for focus adjustment having the negative refractive power closest to the screen
Is composed of, in order from the screen side, a negative meniscus lens L1 convex to the screen side and a positive meniscus lens L2 convex to the screen side. The variable magnification lens group G2 located in the middle has, in order from the screen side, a positive lens L3 having a strong convex surface on the screen side, a biconcave negative lens L4, and a positive convex surface having a strong convex surface on the condensing optical system side. It is composed of a lens L5 and a positive meniscus lens L6 which is convex toward the condensing optical system.

Further, the lens group G3 for correction closest to the condensing optical system 3 is composed of a negative lens L7 having a biconcave surface.

The projection zoom lens 10 of this example is also a zoom lens that can obtain a clear projection image that has been magnified by the correction lens group G3 without moving the projection surface or the like.

Therefore, by adopting the projection zoom lens of this example, it is possible to realize a compact, lightweight, and inexpensive projection device having a magnifying function. Further, the zoom lens group G2 of this example also satisfies the formula (1) as in the above-described embodiment, and the projection zoom lens itself can be made compact. Further, the combination of the refracting powers of the lenses L1 to L7 of the projection zoom lens of the present example is an objective combination as compared with the combination of the lenses of the first embodiment such as negative, positive, positive, negative, positive, positive, and negative. It is configured so that Therefore, the focus position of the condensing optical system can be set to a position substantially near the center of the projection zoom lens 10. As a result, the diameter of each lens that constitutes the projection zoom lens 10 can be reduced, so that the projection zoom lens can be downsized.

Lens data r ₁ = 175.673 d ₁ = 2.650 n ₁ = 1.80610 ν ₁ ＝ 40.95 r ₂ ＝ 43.601 d ₂ ＝ 5.590 r ₃ ＝ 45.143 d ₃ ＝ 6.500 n ₂ ＝ 1.84666 ν ₂ ＝ 23.78 r ₄ ＝ 67.975 d _{4 = 7.487~ 31.620 r 5 = 53.957} d 5 = 10.550 n 3 = 1.80100 ν 3 = 34.97 r 6 = -195.073 d 6 = 3.730 r 7 = -65.289 d 7 = 2.500 n 4 = 1.84666 ν 4 = 23.78 r 8 = _{65.289 d 8 = 2.280 r 9 =} 200.695 d 9 = 6.400 n 5 = 1.48749 ν 5 = 70.21 r 10 = -68.257 d 10 = 4.580 r 11 = -129.775 d 11 = 6.100 n 6 = 1.76182 ν 6 = 26.55 r 12 = _{-55.891 d 12 = 24.357~ 1.000 r 13} = -258.302 d 13 = 3.000 n 7 = 1.48749 ν 7 = 70.21 r 14 = 258.302 projection distance W1 1840Mm product image distance W2 2257.2Mm focal length standard (telephoto end) 299. 77mm magnification (wide-angle end) 244.85mm Imaging magnification standard (telephoto end) -0.190 magnification (Wide angle end) -0.145 magnification 1.310 zooming lens group G2 imaging magnification standard (telephoto end) β _T -1.130 expansion (wide angle end) beta _W of -0.8639 condensing optical system Focusing position 361 mm (distance from projection surface to screen side) FIGS. 7 and 8 show spherical aberration, astigmatism and distortion at the wide-angle end and the telephoto end of the projection zoom lens of this example, respectively. 9 and 10 are lateral aberration diagrams of the projection zoom lens of this example, respectively. A tangential ray (T) and a sagittal ray (S) are shown in the astigmatism diagram and the lateral aberration diagram, and d line, g line, and C line are shown in the spherical aberration diagram and the lateral aberration diagram. The numerical aperture (NA) is 0.02
It is 3.

[Third Embodiment] FIG. 11 shows a third embodiment of the present invention.
Projection zoom lens 10 and OHP using the same
The optical system of is shown. FIG. 11A shows the position of the lens at the telephoto end in the standard state, FIG. 11B shows the intermediate position, and FIG. 11C shows the lens position at the wide-angle end in the enlarged state. It is shown. This embodiment is also shown using the condensing optical system 3 using the Fresnel lens 1,
The common parts are given the same reference numerals and the description thereof is omitted. The projection zoom lens 10 of this example is divided into three lens groups G1 to G3 from the screen 5 side.
The lens group G2 for zooming has two sub-lens groups G2a.
And G2b. The detailed data of each lens are as shown below.

The focus adjusting lens group G1 having the most negative refractive power on the screen side comprises, in order from the screen side, a positive lens L1 having a strong convex surface on the side of the focusing optical system, and a biconcave negative lens. It is composed of L2. The lens group G2 for zooming has a two-group structure, and the lens group G2a on the screen side is composed of a positive lens L3 having a strong convex surface on the screen side. In addition, the next lens group G2b
Is, in order from the screen side, a biconvex positive lens L4, a negative lens L5 having a strong concave surface on the screen side, a positive lens L6 having a strong convex surface on the condensing optical system side, and a strong condensing optical system side. It is composed of a positive lens L7 having a convex surface. The correcting lens group G3 is composed of a negative lens L8 having a strong concave surface on the side of the condensing optical system.

The projection zoom lens 10 of the present example is also a zoom lens that can obtain a sharp projected image with a variable magnification by the correction lens group G3 without moving the projection surface or the like. Further, the lens group G2 for zooming is set to G2a and G2.
In the two-lens configuration of b, lens groups G2a and G2b are provided at the telephoto end.
And the air gap between the lens groups G2a and G2b is widened at the wide-angle end. As a result, high magnification can be realized in a state where the moving distance of the lens group G2 for zooming is small,
Further, since the focal length of the lens for zooming is shortened in order to obtain high magnification and various aberrations are not deteriorated, it is easy to improve various aberrations. Therefore, it is possible to obtain a compact zoom lens for projection with good aberration. With such a configuration, the projection zoom lens of this example achieves a magnifying power of almost 2 times, and by using the projection zoom lens of this example, a compact, lightweight, and high-magnification projection device is provided at low cost. can do. Further, the zoom lens group G2 of this example also satisfies the formula (1) as in the above embodiment, and in this respect as well, the projection zoom lens and the projection apparatus are made compact.

Lens data r ₁ = -332.358 d ₁ = 4.900 n ₁ = 1.72825 ν ₁ = 28.46 r ₂ = -90.123 d ₂ = 1.840 r ₃ = -88.753 d ₃ = 2.500 n ₂ = 1.80400 ν ₂ = 46.58 r _{4 = 88.753 d 4 = 6.370~ 36.694 r} 5 = 78.932 d 5 = 3.500 n 3 = 1.76182 ν 3 = 26.55 r 6 = 196.784 d 6 = 2.300~ 29.886 r 7 = 142.832 d 7 = 4.750 n 4 = 1.56732 ν 4 = 42.83 _{r 8 = -142.832 d 8 = 3.680} r 9 = -41.145 d 9 = 2.500 n 5 = 1.78470 ν 5 = 26.22 r 10 = 455.430 d 10 = 0.950 r 11 = -1013.839 d 11 = 10.500 n 6 = 1.48749 ν 6 = 70.21 r ₁₂ = -39.802 d ₁₂ = 0.200 r ₁₃ = 408.568 d ₁₃ = 7.100 n ₇ = 1.80100 ν ₇ = 34.97 r ₁₄ = -100.085 d ₁₄ = 48.910 to 1.000 r ₁₅ = -537.832 d ₁₅ = 3.000 n ₈ = 1.48749 ν ₈ = 70.21 r ₁₆ = 106.100 projection distance W1 1955Mm between product-image distance W2 2398Mm focal length standard (telephoto end) 317 47 mm Magnification (wide-angle end) 185.24 mm Imaging magnification standard (telephoto end) -0.190 Magnification (wide-angle end) -0.0975 Magnification ratio 1.949 Imaging magnification standard of zoom lens group G2 (telephoto end) β _T −1.639 Enlarged (wide-angle end) β _W −0.8556 Condensing position of condensing optical system 390 mm (distance from projection surface to screen side) FIGS. 12 and 13 show the zoom lens for projection of this example. The spherical aberration, the astigmatism, and the distortion at the wide-angle end and the telephoto end are shown. Also, FIG. 14 and FIG.
5 shows lateral aberration diagrams of the projection zoom lens of this example. In the astigmatism diagram and the lateral aberration diagram, the tangential ray (T) and the sagittal ray (S) are shown, and in the spherical aberration diagram and the lateral aberration diagram, the d-line,
The g and C lines are shown. The numerical aperture (NA) is 0.023.

In the above embodiments, a single-plate type optical system such as an OHP is described as an example, but the present invention is not limited to this example, and is used in, for example, a projection type liquid crystal projector. Of course, a 3-plate type optical system may be used. Further, not only the front projection type but also the rear projection type optical system can realize a compact projection apparatus having a magnifying function by using the projection zoom lens of this example. Further, as described above, a mirror or prism may be installed in the projection direction.

[0032]

As described above, the projection zoom lens of the present invention has a simple structure of three lens groups for focus adjustment, magnification change, and correction. You can project a magnified and clear image on the screen without moving the surface. Therefore, it is possible to provide a projection device having a magnifying function with a simple configuration using the projection zoom lens of the present invention, and by omitting a complicated and expensive mechanism such as moving the projection surface, the projection device can be made lighter and smaller. And cost reduction.

Further, the zoom lens for projection can be further downsized by setting the condition of the lens group for zooming to the above-mentioned appropriate range, and the zooming lens group is composed of two groups. This makes it possible to provide a compact and high-magnification projection zoom lens.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a lens of Example 1 of the present invention.

FIG. 2 is a diagram of various types of aberration at the wide-angle end of Example 1.

FIG. 3 is a diagram of various types of aberration at the telephoto end of the first example.

FIG. 4 is a lateral aberration diagram for Example 1 at the wide-angle end.

5 is a lateral aberration diagram for Example 1 at the telephoto end. FIG.

FIG. 6 is a diagram showing a configuration of a lens of Example 2 of the present invention.

FIG. 7 is a diagram of various types of aberration at the wide-angle end of Example 2;

FIG. 8 is a diagram of various types of aberration at the telephoto end of the second example.

9 is a lateral aberration diagram for Example 2 at the wide-angle end. FIG.

10 is a lateral aberration diagram for Example 2 at the telephoto end. FIG.

FIG. 11 is a diagram showing a lens configuration according to example 3 of the present invention.

FIG. 12 is a diagram of various types of aberration at the wide-angle end of Example 3;

FIG. 13 is a diagram of various types of aberration at the telephoto end of the third example.

14 is a lateral aberration diagram for Example 3 at the wide-angle end. FIG.

15 is a lateral aberration diagram for Example 3 at the telephoto end. FIG.

[Explanation of symbols]

 1 ... Fresnel lens 2 ... Projected surface 3 ... Condensing optical system 5 ... Screen 10 ... Projection zoom lens G1 ... Focus adjustment lens group G2 ... Lens group G3 ... Lens group for correction L1-L8 ... Lens

Claims (3)

[Claims] 1. A zoom lens for projection for projecting an image incident from a condensing optical system onto a screen, which is a lens for focus adjustment of a negative refractive power whose position is fixed during zooming in order from the screen side. Group, a lens group for zooming with a positive refracting power that moves in the optical axis direction for zooming, a lens group for focus adjustment, and the optical member for maintaining a constant optical distance between the image. A projection zoom lens, comprising: a lens group for correcting a negative refractive power that moves in the axial direction. 2. The projection zoom lens according to claim 1, wherein an image forming magnification β _W at a wide angle end and an image forming magnification β _T at a telephoto end of the zoom lens group satisfy the following expressions. . | Β _W | <1 <| β _T | where β _W and β _T are image forming magnifications in the reduction optical system. 3. The zoom lens group according to claim 1, comprising a first lens group having a positive refractive power and a second lens group having a positive refractive power in order from the screen side. Then, the zoom lens for projection is characterized in that it moves in the optical axis direction so that the air gap between the first and second lens groups increases on the wide-angle side.