JP2003015037A - Zoom lens for projection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a compact zoom lens for projection capable of maintaining high resolving power, having long back focus required for the arrangement of a color synthesizing optical system and having high telecentricity though it is a wide-angle lens whose half viewing angle is >=30 deg.. SOLUTION: The zoom lens for projection is constituted by successively arranging 1st to 6th negative, positive, positive, negative, positive and positive lens groups I to VI from an enlargement side to a reduction side and providing an aperture diaphragm ST between the 3rd and the 4th lens groups. In the case of consecutively varying power from a wide angle end to a telephoto end, the 1st and the 6th lens groups are fixed and the 2nd to the 5th lens groups are moved on an optical axis to the enlargement side. Then, the focal distance of an entire system at the wide angle end: fw, the focal distance of the 1st lens group: f1, back focus when a conjugate point on the enlargement side is infinity: Bf and the length of the entire system: L satisfy conditions (1) 1.0<Bf/fw (2) 0.9<|f1|fw<1.3 and (3) 3.0<L/fw<4.0.

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 for enlarging and projecting an original image displayed on a liquid crystal panel or the like onto a display medium such as a screen.

[0002]

2. Description of the Related Art Liquid crystal projectors for enlarging and projecting an original image displayed on a liquid crystal panel or the like onto a display medium such as a screen have recently become widespread for displaying video reproduction images and computer data. Among them, the “front projection type three-panel liquid crystal projector” used for presentations and the like has a high penetration rate because of high definition images.

In a three-plate liquid crystal projector, a "light emitted from each liquid crystal panel (two-dimensionally spatially modulated by an image displayed on each liquid crystal panel) emitted from each liquid crystal panel is formed between a projection lens and the liquid crystal panel by a prism or the like. Since it is necessary to arrange a “color synthesizing optical system for synthesizing and making the light incident on the projection lens”, the projection lens must have a “long back focus” to secure a space for deploying the color synthesizing optical system.

Further, the spectral transmittance of the color synthesizing optical system changes depending on the incident angle. Therefore, if the range of change of the incident angle of the light rays entering the color synthesizing optical system from the liquid crystal panel is large, each color in the projected color image will be changed. Brightness changes depending on the angle of view, making the image difficult to see. In order to avoid such a situation, the projection lens is
Telecentric nature of being approximately parallel to the optical axis on the reduction side "
It is preferable to have

From the viewpoint of convenience, the front projection type three-panel liquid crystal projector is capable of varying the magnification of the display image by 1.2 to 1.3 times, and is compact so that it can be easily carried. It is required to project a large screen with a short projection distance. In order to meet such a demand, it is preferable that the projection lens has a zoom function, is not bulky, and has a wide angle of view.

[0006]

SUMMARY OF THE INVENTION In order to meet the above-mentioned demands, the present invention maintains a high resolution even with a wide angle of view of a half field angle of 30 degrees or more, and has a long background required for the arrangement of a color synthesizing optical system. The challenge is to realize a compact zoom lens for projection, which has focus and high telecentricity.

[0007]

As shown in FIG. 1, a "projection zoom lens" according to the present invention has a negative refracting power in order from the enlargement side (left side in the figure) toward the reduction side. 1 lens group I, 2nd lens group II of positive refractive power, 3rd lens group III of positive refractive power, 4th lens group IV of negative refractive power,
A fifth lens group V having a positive refractive power and a sixth lens group VI having a positive refractive power are arranged, and an aperture stop ST is provided between the third and fourth lens groups.

When continuously changing the magnification from the wide-angle end to the telephoto end, the first
The lens group I and the sixth lens group VI are fixed, and the second lens group II, the third lens group III, the fourth lens group IV, and the fifth lens group V are on the optical axis as indicated by arrows. Move to the enlargement side.

When the focal length of the entire system at the wide angle end is fw, the focal length of the first lens unit is f1, the back focus when the conjugate point on the magnification side is infinity is Bf, and the length of the entire system is L , These satisfy the conditions: (1) 1.0 <Bf / fw (2) 0.9 <| f1 | / fw <1.3 (3) 3.0 <L / fw <4.0 (claim) Item 1). Note that focusing is performed by moving the first lens group.

In the zoom lens for projection according to the first aspect of the present invention, when continuously zooming from the wide-angle end to the telephoto end, various displacement modes are available for the displacement of the second lens group to the fifth lens group toward the magnification side. It is possible, but as shown in FIG. 1, "the distance between the third lens group III and the fourth lens group IV is wide" and "the distance between the fourth lens group IV and the fifth lens group V is narrow". Displacement is preferable (Claim 2).

It is preferable that the first lens group in the projection zoom lens according to the first or second aspect of the invention has "all of its constituent lenses are negative lenses". It goes without saying that the negative lens is a “lens having a negative refractive power”. In the projection zoom lens according to the third aspect, all the lenses constituting the first lens group are negative lenses, and at least one of them is an aspherical lens.

The fourth lens group in the projection zoom lens according to the first, second or third aspect is that "a negative lens having a large curvature on the reduction side and a negative lens having a large curvature on the expansion side are arranged in order from the enlargement side. It is preferable that the configuration is “smooth” (claim 4).

The second lens group in the projection zoom lens according to any one of claims 1 to 4 is "1 sheet or 2 sheets".
It is preferable that the positive lens is composed of one positive lens, and the refractive index for the d-line of these one or two positive lenses: N2 satisfies the following condition: (4) 1.7 <N2 ”. 5).
It goes without saying that the positive lens is a “lens having a positive refractive power”.

The third lens group in the projection zoom lens according to any one of claims 1 to 5 has "a positive lens and a negative lens, the positive lens has an Abbe number of ν3p, and the negative lens has an Abbe number. Is ν3n, these satisfy the condition: (5) 15 <ν3p-ν3n ”(claim 6). in this case,
The positive lens and the negative lens of the third lens group may be “bonded lenses (joint lenses)” (claim 7) or “arranged with a minute air gap” (claim). 8).

It is preferable to dispose "a lens having at least one aspherical surface" in the fifth lens group or the sixth lens group in the projection zoom lens according to any one of claims 1 to 8 (claim). Item 9).

When the first lens group has an aspherical lens as in the zoom lens for projection according to the third aspect, the sixth lens group includes "a lens having at least one aspherical surface".
And a lens having an aspherical surface in the first lens group and the sixth lens group is a "plastic lens", and the "absolute value of synthetic refractive power" of the plastic lens having an aspherical surface is defined as It is preferably 5% or less of the refractive power (claim 10).

In the projection zoom lens according to claim 9, it is possible to "arrange a lens having an aspherical surface in the fifth lens group and use this lens as a hybrid lens" (claim 11).

The sixth lens group in the projection zoom lens according to any one of claims 1 to 11 can be "constituted by one positive lens" (claim 12), and in this case, the sixth lens group. It is preferable that the Abbe number: ν6 of one positive lens constituting the lens group satisfies the condition: (6) 50 <ν6 (claim 13).

The projection zoom lens of the present invention has a "negative lead" in which the first lens group having negative refracting power is at the head in order to have a wide angle of view and a long back focus.
Type zoom lens.

Conditional expression (1) is a condition for satisfying both "long back focus and large angle of view" required for the projection zoom lens for the three-plate liquid crystal projector, and the focal length of the entire system is the shortest. At the wide-angle end, the reduction-side principal point position is located closer to the light source side (reduction side) than the reduction-side lens surface of the sixth lens group.

If the lower limit of the conditional expression (1): 1.0 is exceeded while maintaining the half angle of view of 30 degrees or more, the back focus becomes short and the arrangement of the color combining optical system becomes difficult.

Conditional expression (2) is for satisfying both "long back focus and good optical performance", and if the lower limit of conditional expression (2): 0.9 is exceeded, the negative value of the first lens group becomes negative. Has an excessively large refracting power, and it becomes difficult to maintain good off-axis aberrations such as coma and field curvature. Also, the upper limit value: 1.
When it exceeds 3, the negative refracting power of the first lens group becomes too small and a desired back focus cannot be obtained.

Conditional expression (3) relates to the "balance between compactness and image performance" of the zoom lens for projection. The lower limit of conditional expression (3) is: while maintaining a half angle of view of 30 degrees or more. When it exceeds 3.0, the refracting power of each lens group becomes excessive, and it becomes difficult to correct spherical aberration, coma aberration, astigmatism, and the like, and a region for moving the lens group cannot be sufficiently secured. The desired zoom ratio cannot be obtained.

On the other hand, when the upper limit value is more than 4.0, the entire length of the projection zoom lens becomes long, the compactness is lost, and the outer diameter and thickness of the lens arranged far from the aperture stop are large. It becomes a high cost lens.

In the zoom lens for projection according to the present invention, the first lens group and the sixth lens group are fixed at the time of zooming, and the zooming is performed by fixing the second lens group to the fifth lens group to the fixed first lens group.
It must be done between the sixth lens groups.

In the zoom lens for projection according to claim 2,
During continuous zooming from the wide-angle end to the telephoto end, the distance between the third lens group and the fourth lens group becomes wide, but at the same time, the distance between the fourth lens group and the fifth lens group becomes narrow, so The overall size of the 5th lens group does not change significantly, the "small space" between the 1st and 6th lens groups is effectively used to obtain a sufficient zoom ratio, and spherical aberration, coma aberration, etc. due to zooming It is possible to suppress variations in various aberrations and maintain good telecentricity.

The distortion aberration structurally generated in the negative-lead zoom lens is the high-order distortion aberration of the opposite sign when the positive lens is arranged "at a position where the off-axis chief ray height is far from the aperture stop to the enlargement side". It is general to try to offset by generating.

However, since this positive lens also has an "action for moving the entrance pupil to the reduction side", if such general distortion aberration cancellation is performed, the lens outer diameter becomes large and it is difficult to widen the angle of view. Becomes

In the projection zoom lens according to the third aspect, all the lenses forming the first lens group are negative lenses to move the entrance pupil to the enlargement side, and the zoom lens for projection is further arranged in the first lens group. By correcting the distortion aberration with the aspherical lens, it is possible to obtain a lens having a wide field angle, a small outer diameter, and a very small distortion aberration.

The aspherical lens is preferably made of plastic which is easy to mold and inexpensive. In each of the examples described below, the aspherical lens is "all plastic lenses", but a so-called hybrid type aspherical lens in which a thin resin layer is formed on the optical surface of the glass lens (referred to as "hybrid lens" in this specification) ) May be used, and of course, an aspherical lens obtained by grinding glass may be used.

In the zoom lens for projection according to the fourth aspect, the fourth lens group includes, in order from the enlargement side, a negative lens having a large curvature on the reduction side and a negative lens having a large curvature on the enlargement side. It has a configuration composed of two negative lenses ", whereby spherical aberration and astigmatism are satisfactorily corrected.

In addition, the above-mentioned "fourth negative lens
Since the "lens group" is located adjacent to the aperture stop where the height of the marginal ray is low, it is effective in reducing the Petzval sum, and the flatness of the image plane can be kept good.

When the second lens group is "composed of one or two positive lenses" as in the zoom lens for projection according to the fifth aspect, the refractive index: N2 of the material of these positive lenses is a conditional expression. When the lower limit of (4): 1.7 is exceeded,
The amount of movement required for zooming becomes large and it becomes difficult to make it compact. If you try to “change the curvature of the positive lens to increase the positive refracting power” to avoid this difficulty, high-order spherical aberration, coma, etc. will occur, and the Petzval sum will increase and the image plane will become flat. It becomes difficult to maintain sex.

In the zoom lens for projection according to the sixth aspect, the third lens group has “a positive lens and a negative lens, and the Abbe number of the positive lens is ν3p and the Abbe number of the negative lens is ν3n.
Satisfies the conditional expression (5), ”
Further, by arranging the positive lens and the negative lens as "a cemented lens" or "arrangement with a minute air gap (claims 7 and 8)", axial chromatic aberration can be satisfactorily corrected.

Further, as in the zoom lens for projection according to claim 9, by disposing a lens having at least one aspherical surface in the fifth lens group or the sixth lens group,
It is possible to correct coma and distortion with a small number of lenses.

Also in the zoom lens for projection according to the ninth aspect, it is desirable that the aspherical lens arranged in the fifth lens group or the sixth lens group is made of plastic which is easy to mold and inexpensive. On the other hand, a lens made of a plastic material has a larger fluctuation in imaging performance due to environmental changes such as temperature and humidity and a relatively smaller refractive index than a glass lens. You cannot give power.

In the zoom lenses for projection shown in Examples 1 to 4 described later, the first lens group and the sixth lens group have aspherical lenses, and the aspherical lenses in the first lens group and the sixth lens group are By changing the "absolute value of the combined refractive power" of the plastic lens having an aspherical surface to 5% or less of the refractive power of the entire system at the wide-angle end, it is possible to significantly change the imaging performance due to environmental changes. It is made small (claim 10). The "ratio of the absolute value of the synthetic refractive power of the aspherical plastic lens to the refractive power at the wide-angle end" is allowed up to about 10% from a practical point of view.

In the zoom lens for projection shown in the fifth embodiment, one lens of the fifth lens group is a hybrid type aspherical lens to realize stable image forming performance against environmental changes.

Since the off-axis chief ray entering the projection zoom lens from the liquid crystal panel has a high telecentricity, it is largely bent in the optical axis direction by the lens having a positive refractive power arranged in the sixth lens group. However, if the "difference in the degree of bending due to the difference in wavelength" of the light rays is large, chromatic aberration of magnification will be large.

In the zoom lens for projection according to the twelfth and thirteenth aspects, the structure is simplified by using only one positive lens forming the sixth lens group, and the Abbe number: ν6 satisfies the conditional expression (6). By selecting the material as described above, the occurrence of lateral chromatic aberration is suppressed.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION Five specific examples will be given below as embodiments.

In each embodiment, "S" is the surface number, "R" is the radius of curvature of each surface (paraxial radius of curvature for aspherical surfaces), and "D" is the surface spacing on the optical axis. Represent For the surface spacing that changes due to zooming, the values at the wide-angle end and at the telephoto end are shown together as "at the wide-angle end / at the telephoto end".

“Nd” and “νd” represent the refractive index and Abbe number of the material of each lens for the d-line. "Fw",
As described above, “ft” is the focal length of the entire system at the wide-angle end and the telephoto end, “f1” is the focal length of the first lens group, and “F / No” is the F-number representing the brightness at the wide-angle end. ,
“Ω” is the half angle of view at the wide-angle end, “obd” is the distance from the screen to the first lens surface (the lens surface on the most magnifying side of the first lens group), and “Bf” is in air (without a prism). ), Back focus, "L" represents the length of the entire system. The unit of the quantity having the dimension of length is "mm".

With respect to the shape of the aspherical surface, with the intersection with the optical axis as the origin, the height with respect to the optical axis: h, the amount of change in the optical axis direction: Z, the paraxial curvature: c (the reciprocal of the paraxial radius of curvature), Cone constant:
K, aspherical coefficients of higher-order terms: A, B, C, D, E,
Well-known formula: Z = c · h ² / [1 + √ {1− (1 + K) · c ² · h ² }] + A · h ⁴ + B · h ⁶
It is represented by + C · h ⁸ + D · h ¹⁰ + E · h ¹² , and is specified by giving values of c (= 1 / R), K, and AE.

Example 1 FIG. 1 shows the lens configuration of a projection zoom lens of Example 1.

From the enlargement side (left side of the drawing), the first negative refractive power
Lens group I, second lens group II having positive refractive power, third lens group III having positive refractive power, aperture stop ST, fourth lens group IV having negative refractive power, fifth lens group having positive refractive power It is configured by arranging V and a sixth lens group IV having a positive refractive power. fw = 27.37, ft = 32.83, f1 = −28.97, F / No = 1.75, ω = 31.9 degrees, obd = 1800, Bf = 31.45, L = 91 S R D Nd νd 1 261.490 2.500 1.61800 63.4 2 23.559 7.408 3 53.969 3.000 1.49154 57.8 4 27.501 9.145 / 4.863 5 42.201 5.613 1.83500 43.0 6 −1060.846 0.200 7 57.481 2.942 1.80610 33.3 8 116.649 13.319 / 10.867 9 37.546 5.674 1.79950 42.3 10 −18.766 11 141.669 1.083 12 ∞ (aperture) 0.400 / 5.342 13 171.830 2.000 1.48749 70.4 14 23.447 8.454 15 −15.322 2.000 1.58144 40.9 16 −39.958 1.286 / 0.300 17 269.662 2.000 1.84666 23.8 18 36.487 8.494 1.49700 81.6 19 −36.952 0.200 20 87.975 9.399 1.78590 43.9 21 −43.464 0.300 / 3.077 22 687.650 3.584 1.49154 57.8 23 −77.873 1.000 23 ∞ 37.500 1.51680 64.2 24 ∞ 6.137 Aspherical fourth surface K = −1.257865, A = −0.572880 × 10 ⁻⁵ , B = −0.231412 × 10 ⁻⁸ , C = -0.286616 x 10 ^-10 , D = 0.764947 x 10 ^-13 , E = -0.1316 58 × 10 ⁻¹⁵ 23rd surface K = −6.672815, A = 0.579493 × 10 ⁻⁵ , B = −0.516467 × 10 ⁻⁸ , C = 0.735567 × 10 ⁻¹¹ , D = −0.773526 × 10 ⁻¹⁴ , E = 0.545654 × 10 ^-17 condition value (1) Bf / fw = 1.15 (2) | f1 | /fw=1.06 (3) L / fw = 3.32 (4) N2 = 1.80610 (5 ) Ν3p-ν3n = 16.8 (6) ν6 = 57.8 The ratio of the absolute value of the synthetic refractive power of the plastic aspherical lens to the refractive power of the entire system at the wide-angle end: 3.9
As the value of the conditional expression (4), the smallest value among the target numerical values is displayed. The same applies to the other examples.

2 and 3 are diagrams showing spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of the first embodiment, and FIGS. 4 and 5 similarly show the wide-angle end and the telephoto end. 6 is a diagram showing coma aberration in FIG.

Each aberration diagram shows the aberration of green light having a wavelength of 546 nm, but the spherical aberration diagram and the coma aberration diagram also show the aberrations of wavelengths of 610 nm and 460 nm on behalf of red and blue light. ing. Further, S in the astigmatism diagram is the aberration of the sagittal image plane, and M is the aberration of the meridional image plane, and the same applies to the aberration diagrams of other examples.

Example 2 FIG. 6 shows the lens arrangement of a projection zoom lens of Example 2 in accordance with FIG. fw = 27.38, ft = 32.83, f1 = −27.21, F / No = 1.75, ω = 31.9 degrees, obd = 1800, Bf = 31.43, L = 93 SR D Nd νd 1 177.720 2.500 1.61800 63.4 2 43.276 1.386 3 60.000 2.500 1.71300 53.9 4 26.339 6.097 5 48.861 3.000 1.49154 57.8 6 26.137 9.233 / 5.306 7 38.291 5.995 1.83500 43.0 8 −1690.836 0.200 9 51.241 3.105 1.71736 29.5 10 104.496 12.131 / 10. 1.72916 54.7 12 −36.083 2.000 1.80518 25.5 13 528.993 1.012 14 ∞ (Aperture) 0.400 / 4.691 15 146.407 2.000 1.48749 70.4 16 21.511 7.612 17 −14.766 2.000 1.58144 40.9 18 −40.129 1.491 / 0.300 19 809.035 2.000 1.84666 23.8 20 35.391 8.327 1.49700 81.6 −39.310 0.200 22 101.622 9.649 1.78590 43.9 23 −40.835 0.300 / 3.134 24 148.946 4.649 1.49154 57.8 25 −89.092 1.000 26 ∞ 37.500 1.51680 64.2 27 ∞ 6.122 Aspheric 6th surface K = −1.131913, A = −0.508730 × 10 ⁻⁵ , B = 0.356915 x 10 ^-8 , C = -0.285476 x 10 ^-10 , D = 0.649020 x 10 ^-13 , E = -0.732945 x 10 ^-16 25th surface K = -7.768119, A = 0.548459 x 10 ^-5 , B = -0.666492 x 10 ^-8 , C = 0.821118 x 10 ^-11 , D = −0.621957 × 10 ⁻¹⁴ , E = 0.259950 × 10 ⁻¹⁷ Conditional expression value (1) Bf / fw = 1.15 (2) | f1 | /fw=0.99 (3) L / fw = 3 .40 (4) N2 = 1.717360 (5) ν3p-ν3n = 29.2 (6) ν6 = 57.8 The absolute value of the synthetic refractive power of the plastic aspherical lens is the refraction of the entire system at the wide-angle end. Ratio to power: 1.1
%, The wide-angle end of the projection zoom lens of the second embodiment,
Shows spherical aberration, astigmatism, and distortion at the telephoto end,
9 and 10 similarly show coma.

Example 3 FIG. 11 shows the lens arrangement of the projection zoom lens of Example 3 in the same manner as in FIG. fw = 27.39, t = 32.85, f1 = −31.22, F / No = 1.75, ω = 31.9 degrees, obd = 1800, Bf = 31.45, L = 100 S RD Nd νd 1 324.672 2.500 1.61800 63.4 2 24.268 6.884 3 47.790 3.000 1.49154 57.8 4 28.402 11.865 / 4.818 5 51.543 6.275 1.83500 43.0 6 −164.331 19.942 / 21.573 7 30.094 5.738 1.72916 54.7 8 −41.272 2.960 1.80518 25.5 9 107.037 0.200 10 0.400 / 2.974 11 −274.226 2.000 1.64769 33.8 12 −200.936 0.200 13 −111.943 1.500 1.48749 70.4 14 20.600 9.824 15 −16.663 2.000 1.58144 40.9 16 −38.374 1.535 / 0.300 17 1107.230 3.260 1.84666 23.8 18 35.845 7.453 1.49700 81.6 19 −42.142 0.210 20 82.826 8.099 1.78590 43.9 21 −45.536 0.300 / 4.377 22 −331.928 3.855 1.49154 57.8 23 −61.073 1.000 23 ∞ 37.500 1.51680 64.2 24 ∞ 6.134 Aspherical fourth surface K = −1.105017, A = −0.496367 × 10 ⁻⁵ , B = −0.570986 × 10 ⁻⁹ , C = −0.308868 × 10 ⁻¹⁰ , D = 0.780603 × 10 ⁻¹³ , E = -0.120903 x 10 ^-15 23rd surface K = -3.193172, A = 0.476118 x 10 ^-5 , B = -0.648537 x 10 ^-8 , C = 0.655050 x 10 ^-11 , D = 0.169816 x 10 ^-15 , E = −0.607502 × 10 ⁻¹⁷ Conditional expression value (1) Bf / fw = 1.15 (2) | f1 | /fw=1.14 (3) L / fw = 3.65 (4) N2 = 1 .835000 (5) ν3p-ν3n = 29.2 (6) ν6 = 57.8 The ratio of the absolute value of the synthetic refractive power of the plastic aspherical lens to the refractive power of the entire system at the wide-angle end: 0.2
% FIGS. 12 and 13 show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of Example 3, and FIGS. 14 and 15 similarly show coma.

Example 4 FIG. 16 shows the lens arrangement of a projection zoom lens of Example 4 in the same manner as in FIG.

The negative lens and the positive lens of the third lens group are arranged adjacent to each other with a small air gap. fw = 27.38, ft = 32.85, f1 = −31.68, F / No = 1.75, ω = 31.9 degrees, obd = 1800, Bf = 31.43, L = 95 S RD Nd νd 1 204.353 2.500 1.61800 63.4 2 24.832 6.457 3 75.502 3.000 1.49154 57.8 4 33.264 13.065 / 7.397 5 64.327 6.006 1.83500 43.0 6 −107.168 5.478 7 40.264 3.933 1.80610 33.3 8 115.064 7.086 / 6.690 9 1115.272 2.649 1.80518 25.5 10 26.990 9.1115.272 2.649 1.80518 25.5 10 26.990 1.72916 54.7 12 −63.430 0.754 13 ∞ (aperture) 0.400 / 4.445 14 347.478 2.269 1.48749 70.4 15 22.941 9.289 16 −15.002 2.000 1.58144 40.9 17 −55.782 0.755 / 0.300 18 257.792 2.000 1.84666 23.8 19 36.897 8.335 1.49700 81.6 20 −33.577 0.226 21 83.026 9.156 1.78590 43.9 22 −43.877 0.300 / 2.774 23 −166.982 3.473 1.49154 57.8 24 −49.406 1.000 25 ∞ 37.500 1.51680 64.2 26 ∞ 6.122 Aspherical fourth surface K = −0.995546, A = −0.407688 × 10 ⁻⁵ , B = 0.245732 × ^{10 -8, C = -0.307065 × 10} -10, D = 0.710988 × 10 -13 E = -0.967827 × 10 ^-16 24th surface K = -3.392102, A = 0.524904 × 10 -5, B = -0.498802 × 10 -8, C = 0.821965 × 10 -11, D = -0.885412 × 10 -14, E = 0.621729 × 10 ⁻¹⁷ Conditional expression value (1) Bf / fw = 1.15 (2) | f1 | /fw=1.16 (3) L / fw = 3.47 (4) N2 = 1. 80610 (5) ν3p-ν3n = 29.2 (6) ν6 = 57.8 The ratio of the absolute value of the synthetic refractive power of the plastic aspherical lens to the refractive power of the entire system at the wide-angle end: 2.7.
% FIGS. 17 and 18 show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of Example 4, and FIGS. 19 and 20 similarly show coma.

Example 5 FIG. 21 shows the lens arrangement of the projection zoom lens of Example 5 in the same manner as in FIG.

A hybrid aspherical lens is arranged in the fifth lens group. fw = 27.40, ft = 32.86, f1 = −30.50, F / No = 2.06, ω = 31.9 degrees, obd = 1800, Bf = 31.85, L = 95 S RD Nd νd 1 87.546 2.500 1.58913 61.3 2 22.567 12.829 3 188.474 3.000 1.49154 57.8 4 36.812 6.653 / 2.000 5 55.793 5.263 1.83500 43.0 6 −150.166 16.704 / 16.117 7 30.957 5.051 1.72916 54.7 8 −39.738 2.000 1.80518 25.5 9 −94.874 2.145 ) 0.893 / 3.802 11 311.905 3.207 1.49700 81.6 12 17.548 9.064 13 −13.132 2.083 1.68893 31.2 14 −22.013 2.080 / 0.500 15 −195.716 2.000 1.84666 23.8 16 107.843 9.963 1.49700 81.6 17 −21.949 0.200 1.52020 52.0 18 −20.985 0.500 / 4.412 19 71.885 8.865 1.61800 63.4 20 −55.697 1.000 21 ∞ 37.500 1.51680 64.2 22 ∞ 6.128 Aspherical fourth surface K = −1.226703, A = −0.358978 × 10 ⁻⁵ , B = 0.793869 × 10 ⁻¹⁰ , C = 0.161587 × 10 ⁻¹⁰ , D ^{= -0.133185 × 10 -12, E =} 0.186512 × 10 -15 18th surface K = -0.099884, A = 0.688650 × 10 ^{5, B = -0.276573 × 10 -7} , C = 0.213846 × 10 -9, D = -0.608649 × 10 -12, E = 0.804134 × 10 -15 Condition value (1) Bf / fw = 1.16 ( 2) | f1 | /fw=1.11 (3) L / fw = 3.47 (4) N2 = 1.835000 (5) ν3p−ν3n = 29.2 (6) ν6 = 63.4 23 shows spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of Example 5, and FIGS. 24 and 25 also show coma.

In each of the drawings showing the lens structure, the symbol P indicates a "color synthesizing prism" as a color synthesizing means.

In each of the projection zoom lenses of Examples 1 to 5 listed above, the first lens group I having a negative refractive power and the second lens group having a positive refractive power are arranged from the enlargement side to the reduction side. II,
A third lens group III having a positive refractive power, a fourth lens group IV having a negative refractive power, a fifth lens group V having a positive refractive power, and a sixth lens group VI having a positive refractive power are arranged, An aperture stop ST is provided between the fourth lens groups, and when continuously zooming from the wide-angle end to the telephoto end, the first and sixth lens groups are fixed, and the second to fifth lens groups are on the optical axis. In the projection zoom lens that moves to the magnification side, the focal length of the entire system at the wide-angle end is f
w, the focal length of the first lens group is f1, the back focus when the conjugate point on the magnification side is infinity is Bf, and the length of the entire system is L, these are the conditions: (1) 1.0 < Bf / fw (2) 0.9 <| f1 | / fw <1.3 (3) 3.0 <L / fw <4.0 are satisfied (claim 1).

Further, when zooming continuously from the wide-angle end to the telephoto end, the distance between the third lens group III and the fourth lens group IV becomes wide, and the distance between the fourth lens group IV and the fifth lens group V becomes narrow. (Claim 2), the first lens group I is composed of all negative lenses, and at least one is an aspherical lens (Claim 3).

The fourth lens group IV is composed of a negative lens having a large curvature on the reduction side and a negative lens having a large curvature on the enlargement side in this order from the expansion side (claim 4).
The second lens group II is composed of one element (Examples 3 and 5) or two positive lenses (Examples 1, 2, and 4), and the refractive index of the one or two positive lenses with respect to the d-line: N2 satisfies the condition: (4) 1.7 <N2 (Claim 5).

The third lens group III has a positive lens and a negative lens, and the Abbe number of the positive lens: ν3p and the Abbe number of the negative lens: ν3n satisfy the condition: (5) 15 <ν3p-ν3n. 6).

Further, in Examples 1, 2, 3 and 5, the positive lens and the negative lens of the third lens group III are cemented together (claim 7), and in Example 4, the third lens group III.
The positive lens and the negative lens are “arranged with a minute air gap” (claim 8).

In each of Examples 1 to 5, a lens having at least one aspherical surface is disposed in the fifth lens group V or the sixth lens group VI (claim 9).
A lens having at least one aspherical surface is arranged in the lens group I and the sixth lens group, the lens having an aspherical surface is a plastic lens, and the absolute value of the combined refractive power of the plastic lens having an aspherical surface is It is set to 5% or less of the refractive power of the entire system at the wide-angle end (claim 10).

In Example 5, a lens having an aspherical surface is arranged in the fifth lens group V, and this lens is a hybrid lens (claim 11). In addition, Examples 1 to 5
In both cases, the sixth lens group VI is constituted by "one positive lens" (claim 12), and the Abbe number: ν6 of one positive lens constituting the sixth lens group VI is the condition: (6) 50 <It satisfies ν6.

[0063]

As described above, according to the present invention, a compact projection having a wide field angle of 30 degrees or more and maintaining a high resolution, a long back focus and a high telecentricity. Zoom lens can be realized.

[Brief description of drawings]

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

FIG. 2 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 1.

FIG. 3 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end in the first embodiment.

FIG. 4 is a diagram showing coma aberration at the wide-angle end in Example 1.

FIG. 5 is a diagram showing coma aberration at the telephoto end in the first embodiment.

6 is a lens configuration diagram of a projection zoom lens of Example 2. FIG.

FIG. 7 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 2.

FIG. 8 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the second embodiment.

FIG. 9 is a diagram showing coma at the wide-angle end according to the second embodiment.

FIG. 10 is a diagram showing coma at the telephoto end according to the second embodiment.

FIG. 11 is a lens configuration diagram of a projection zoom lens of Example 3;

FIG. 12 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 3.

FIG. 13 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of Example 3;

FIG. 14 is a diagram showing coma at the wide-angle end according to the third embodiment.

FIG. 15 is a diagram showing coma at the telephoto end according to the third embodiment.

16 is a lens configuration diagram of a projection zoom lens of Example 4. FIG.

FIG. 17 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 4.

FIG. 18 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the fourth embodiment.

FIG. 19 is a diagram showing coma aberration at the wide-angle end according to Example 4;

FIG. 20 is a diagram showing coma aberration at the telephoto end of the fourth embodiment.

21 is a lens configuration diagram of a projection zoom lens of Example 5. FIG.

FIG. 22 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of Example 5.

FIG. 23 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the fifth example.

FIG. 24 is a diagram showing coma aberration at the wide-angle end according to Example 5;

FIG. 25 is a diagram showing coma aberration at the telephoto end of Example 5;

[Explanation of symbols]

I First lens group II Second lens group III Third lens group IV 4th lens group V Fifth lens group VI 6th lens group ST aperture stop P color synthesis prism

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA06 NA02 PA08 PA10 PA11                       PA18 PA19 PB11 PB12 PB13                       QA02 QA07 QA17 QA22 QA25                       QA26 QA34 QA41 QA45 RA05                       RA12 RA13 RA36 RA41 SA57                       UA01

Claims (13)

[Claims] 1. A first lens unit having a negative refracting power, a second lens unit having a positive refracting power, a third lens unit having a positive refracting power, and a negative refracting power A fourth lens group, a fifth lens group having a positive refracting power, and a sixth lens group having a positive refracting power are arranged, and an aperture stop is provided between the third and fourth lens groups. In the zoom lens for projection in which the first and sixth lens groups are fixed and the second to fifth lens groups are moved toward the enlargement side on the optical axis during continuous zooming to the end, When the focal length is fw, the focal length of the first lens unit is f1, the back focus when the conjugate point on the magnification side is infinity is Bf, and the length of the entire system is L, these are the conditions: (1) 1 0.0 <Bf / fw (2) 0.9 <| f1 | / fw <1.3 (3) 3.0 <L / fw <4.0 are satisfied. Projection zoom lens according to claim Rukoto. 2. The projection zoom lens according to claim 1, wherein when the magnification is continuously varied from the wide-angle end to the telephoto end, the distance between the third lens group and the fourth lens group becomes wide, and the fourth lens group and the fifth lens group. A projection zoom lens characterized in that the distance between the lens groups is narrowed. 3. The projection zoom lens according to claim 1, wherein the first lens group is composed of all negative lenses, and at least one of them is an aspherical lens. 4. The zoom lens for projection according to claim 1, 2 or 3, wherein the fourth lens group has, in order from the enlargement side, a negative lens having a large curvature on the reduction side and a negative lens having a large curvature on the enlargement side. A zoom lens for projection, which is configured by arranging 5. The zoom lens for projection according to any one of claims 1 to 4, wherein the second lens group is composed of one or two positive lenses, and the one or two positive lenses are included. The zoom lens for projection is characterized in that the refractive index with respect to the d-line: N2 satisfies the condition: (4) 1.7 <N2. 6. The zoom lens for projection according to any one of claims 1 to 5, wherein the third lens group has a positive lens and a negative lens, the Abbe number of the positive lens is ν3p, and the negative lens is the negative lens. Abbe number of ν3n
Then, the zoom lens for projection is characterized by satisfying the following conditions: (5) 15 <ν3p−ν3n. 7. The projection lens according to claim 6, wherein the positive lens and the negative lens of the third lens group are cemented together. 8. The projection zoom lens according to claim 6, wherein the positive lens and the negative lens of the third lens group are arranged with a minute air gap. 9. The zoom lens for projection according to any one of claims 1 to 8, wherein a lens having at least one aspherical surface is arranged in the fifth lens group or the sixth lens group. A zoom lens for projection. 10. The zoom lens for projection according to claim 3, wherein a lens having at least one aspherical surface is arranged in the sixth lens group, and the lens having an aspherical surface is a plastic lens having an aspherical surface. The absolute value of the synthetic refractive power of the plastic lens is 5% of the total refractive power at the wide-angle end.
A projection zoom lens characterized by the following. 11. The projection zoom lens according to claim 9, wherein a lens having an aspherical surface is arranged in the fifth lens group, and this lens is a hybrid lens. 12. The projection zoom lens according to any one of claims 1 to 11, wherein the sixth lens group is composed of one positive lens. 13. The projection zoom lens according to claim 12, wherein the Abbe number of one positive lens constituting the sixth lens group is ν
6 is a condition: (6) A zoom lens for projection, which satisfies 50 <ν6.