JP4599071B2 - Zoom lens and image projection apparatus having the same - Google Patents

Description

  The present invention relates to a zoom lens, and is suitable for a liquid crystal projector, for example.

  2. Description of the Related Art Conventionally, various liquid crystal projectors (image projection apparatuses) that use an image display element such as a liquid crystal display element to project an image displayed on the display element onto a screen surface have been proposed.

  In particular, liquid crystal projectors have been widely used for conferences and presentations as devices capable of projecting images from a personal computer or the like on a large screen. In recent years, miniaturized liquid crystal projectors for home theaters have been popularized, and the size of liquid crystal display elements tends to be miniaturized.

  In a three-plate type color liquid crystal projector using three liquid crystal display elements, light from a white light source is separated into red, green and blue color lights by a color separation means and guided to the liquid crystal display elements. Then, the color light modulated by the liquid crystal display element is synthesized by color synthesis means such as a dichroic prism and a polarizing plate and guided to the projection lens. For this reason, the projection lens must have a space between the liquid crystal display element and the projection lens for arranging these elements constituting the color synthesizing means, and the projection lens requires a certain length of back focus. Has been.

  In addition, as a projection optical system used in a color liquid crystal projector, when the incident angle to the color composition film provided in the dichroic prism constituting the color composition means changes, the spectral transmittance changes, and the projected image has color unevenness. It is a so-called telecentric optical system in which the pupil on the liquid crystal display element (reduction) side is at an infinite distance in order to minimize the influence of angle dependency such as occurrence and to ensure good pupil matching with the illumination system. Is desired.

  In addition, when a picture (image) of a liquid crystal display element of three colors is combined and projected on the screen, the pixels of each color are displayed on the screen so that the characters on the personal computer are doubled and the resolution and quality are not impaired. Must be superimposed over the entire area. For this reason, it is desired that the color shift (magnification chromatic aberration) occurring in the projection lens is well corrected in the visible light band.

  Furthermore, the distortion is sufficiently corrected so that the projected image is not distorted and unsightly at the contour portion (especially if there is a sudden change in distortion at the periphery and the middle portion, etc., the image quality deteriorates). And a bright lens system having a small F number is required to capture a large amount of light from the light source means.

  Recently, while there is a need for high screen brightness and high image definition, projectors equipped with small panels are strongly required to be compact and lightweight with emphasis on mobility. Furthermore, there is a demand for a zoom lens that can easily adjust the projection screen size by increasing the brightness and widening the angle of view so that it can be brightly projected at a shorter projection distance and can be projected on a large screen in a narrow room.

  Conventionally, a projection lens for a liquid crystal projector is composed of a total of six lens groups each consisting of a negative, positive, positive, negative, positive, and positive refractive power lens group in order from the enlargement side (front side). There is known a 6-group zoom lens that performs zooming by appropriately moving the lens group (for example, Patent Document 1).

  In addition, as a projection lens for a liquid crystal projector, a total of five lens groups each including negative, positive, negative, positive, and positive refractive power groups are arranged in order from the enlargement side. There is known a five-group zoom lens that is moved to a zoom ratio and zoomed (for example, Patent Document 2).

  On the other hand, an aspheric lens is used to correct aberration without increasing the number of lenses in the zoom lens, and an aspheric lens made of a plastic material is used from the viewpoint of ease of processing and manufacturing cost.

For example, in a three-group zoom lens including negative, positive, and positive refractive power lens groups in order from the object side, a zoom lens using an aspheric lens made of a plastic material for each lens group is known (Patent Document 3). .
JP 2001-108900 A JP 2001-066499 A JP 2003-0050352 A

  An aspheric lens made of a plastic material is easier to manufacture than an aspheric lens made of a glass material, and can easily take a large amount of aspheric surface and easily correct aberrations of the optical system.

  On the other hand, if there is an environmental change, for example, if there is a temperature change, the refractive index, thickness, surface shape, etc. of the material will change significantly, and optical characteristics such as focus fluctuation will tend to change greatly.

  For example, in a zoom lens used in a liquid crystal projector, when a lens made of a plastic material is used, each lens constituting the zoom lens is heated by an installation temperature environment, heat generated by an illumination lamp, and the like. Since there are many changes in the refractive index, a lot of defocusing occurs as the optical characteristics deteriorate.

  The present invention relates to a zoom lens capable of suppressing a change in optical performance such as a focus shift due to a temperature change or the like even when an aspherical lens made of a plastic material is used to satisfactorily correct aberrations, and an image projection apparatus having the same The purpose is to provide.

The zoom lens according to the present invention includes, in order from the front to the rear, a first lens group having a negative refractive power that does not move for zooming, 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, a fifth lens group having a positive refractive power, and a sixth lens group having a positive refractive power that does not move due to zooming. During zooming from the wide-angle end to the telephoto end, A zoom lens in which each of the second to fifth lens groups independently moves forward ,
A positive lens made of a plastic material and having at least one front or rear aspherical surface;
It is made of a plastic material, and at least one front or rear surface has an aspherical negative lens,
The focal length of the positive lens made of the i-th plastic material included in the zoom lens is fpi,
The focal length of the negative lens made of the jth plastic material included in the zoom lens is fni,
age,

-0.56 <fn / fp ≦ −0.32
It is characterized by satisfying.

-0.56 <fn / fp <-0.05
It is characterized by satisfying.

  According to the present invention, it is possible to realize a zoom lens in which a focus shift and a change in optical performance due to an environmental change such as a temperature rise are suppressed. Further, by using an aspherical lens, it is possible to realize a retrofocus type zoom lens having a large aperture, a wide angle of view, and a high zoom ratio in spite of a small number of constituent lenses.

  Embodiments of the zoom lens according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a main part schematic diagram of an image projection apparatus (liquid crystal video projector) using a zoom lens according to a first embodiment of the present invention. 2A and 2B show an object distance (distance from the first lens group) of 1.7 m when a numerical value of Numerical Example 1 described later corresponding to Example 1 of the present invention is expressed in mm. It is an aberration diagram at the zoom position at the time of wide angle end (short focal length end) and telephoto end (long focal length end).

  FIG. 3 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using the zoom lens according to the second embodiment of the present invention. 4 (A) and 4 (B) show an object distance (distance from the first lens group) of 1.7 m when the numerical value of Numerical Example 2 described later corresponding to Example 2 of the present invention is expressed in mm. It is an aberration diagram at the zoom position at the time of wide angle end (short focal length end) and telephoto end (long focal length end).

  FIG. 5 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using the zoom lens according to the third embodiment of the present invention. 6 (A) and 6 (B) show an object distance (distance from the first lens group) of 1.7 m when a numerical value of Numerical Example 3 described later corresponding to Example 3 of the present invention is expressed in mm. It is an aberration diagram at the zoom position at the time of wide angle end (short focal length end) and telephoto end (long focal length end).

  FIG. 7 is a schematic view of a main part of an image projection apparatus (liquid crystal video projector) using a zoom lens according to Embodiment 4 of the present invention. FIGS. 8A and 8B show an object distance (distance from the first lens group) of 1.7 m when a numerical value of Numerical Example 4 (to be described later) corresponding to Example 4 of the present invention is expressed in mm. It is an aberration diagram at the zoom position at the time of wide angle end (short focal length end) and telephoto end (long focal length end).

  FIG. 9 is a schematic view of a main part of an image projection apparatus (liquid crystal video projector) using a zoom lens according to Embodiment 5 of the present invention. FIGS. 10A and 10B show an object distance (distance from the first lens group) of 2.3 m when a numerical value of Numerical Example 5 described later corresponding to Example 5 of the present invention is expressed in mm. It is an aberration diagram at the zoom position at the time of wide angle end (short focal length end) and telephoto end (long focal length end).

  In the image projection apparatuses according to the first to fifth embodiments shown in FIGS. 1, 3, 5, 7, and 9, an original image (projected image) displayed on a liquid crystal panel LCD or the like is a zoom lens (projection lens, projection lens) PL. Is used to show an enlarged projection on the screen surface SO.

  SO is a screen surface (projection surface), and LCD is an original image (projected image) such as a liquid crystal panel (liquid crystal display element). The screen surface SO and the original image LCD are in a conjugate relationship. In general, the screen surface SO is reduced to the enlargement conjugate side (front side) at the conjugate point with the longer distance, and the original image LCD is reduced at the conjugate point with the shorter distance. It corresponds to the conjugate side (rear side).

  GB is a glass block such as a color synthesis prism, a polarizing filter, and a color filter.

  The zoom lens PL is attached to a liquid crystal video projector main body (not shown) via a connecting member (not shown). The liquid crystal display element LCD side after the glass block GB is included in the projector body.

  In Examples 1 to 4 of FIGS. 1, 3, 5, and 7, L1 is a first lens group having a negative refractive power (power), L2 is a second lens group having a positive refractive power, and L3 is positive. A third lens group having a refractive power, L4 is a fourth lens group having a negative refractive power, L5 is a fifth lens group having a positive refractive power, and L6 is a sixth lens group having a positive refractive power. ST is a stop, which is provided between the third lens unit L3 and the fourth lens unit L4. ASP indicates that the surface is aspherical.

  In Examples 1 to 4, the second lens unit L2, the third lens unit L3, the fourth lens unit L4, and the fifth lens unit L5 are moved to the screen SO as indicated by arrows during zooming from the wide-angle end to the telephoto end zoom position. Each is moved independently.

  For zooming, the first lens unit L1 and the sixth lens unit L6 do not move. Accordingly, the entire length from the first to the sixth lens units is constant during zooming. Focusing is performed by moving the first lens unit L1 on the optical axis. The focusing may be performed by moving the display panel LCD.

  In Example 5 of FIG. 9, L1 is a first lens group having a negative refractive power, L2 is a second lens group having a positive refractive power, L3 is a third lens group having a positive refractive power, and L4 is a positive refractive power. The fourth lens group, L5, is a fifth lens group having a positive refractive power. ST is a stop, which is provided between the third lens unit L3 and the fourth lens unit L4. ASP indicates that the surface is aspherical.

  In Example 5, during zooming from the wide-angle end to the telephoto end, the second lens unit L2, the third lens unit L3, and the fourth lens unit L4 are independently moved toward the screen SO as indicated by arrows. For zooming, the first lens unit L1 and the fifth lens unit L5 do not move.

  Accordingly, the entire length from the first to the fifth lens units is constant during zooming. Focusing is performed by moving the first lens unit L1 on the optical axis. The focusing may be performed by moving the display panel LCD.

  In each of the embodiments described above, a multilayer coating is applied to each lens surface, thereby preventing a decrease in illuminance on the screen surface SO.

  In FIG. 2, FIG. 4, FIG. 6, FIG. 8 and FIG. 10, G represents the aberration at a wavelength of 550 nm, R represents the wavelength at 620 nm, B represents the aberration at the wavelength of 450 nm, S (sagittal image plane tilt), M (meridional). Both image plane tilts indicate aberrations at a wavelength of 550 nm. ω is the angle of view, and F is the F number.

Next, features of the first to fifth embodiments will be described. In each example,
◎ made of plastic material, and at least one surface of the side after the front or the positive lens of an aspherical shape,
Made of plastic material, at least one surface of the side after the front also has a negative lens of an aspherical shape,
The focal length of the positive lens made of the i-th plastic material included in the zoom lens is fpi,
The focal length of the negative lens made of the jth plastic material included in the zoom lens is fni,
age,

-0.56 <fn / fp ≦ −0.32 (1)
Is satisfied.

  Conditional expression (1) has a negative refractive power lens LN made of a plastic material having an aspheric shape effective for aberration correction and a positive refractive power made of a plastic material having an aspheric shape for correcting aberration. The lens LP is included, and their power (refractive power) relationship is specified.

  In general, the lens LP shifts the focus position on the reduction conjugate side in the over direction with a change in the refractive index of the material due to temperature rise, and the lens LN shifts the focus position on the reduction conjugate side in the under direction with a change in the refractive index of the material due to temperature rise. . Therefore, when both are used, since the shift positions of the focus positions make a pair, the focus shift due to the temperature change can be suppressed.

  In a region exceeding the lower limit of the conditional expression (1), the positive refractive power becomes excessively large with respect to the negative refractive power, so the influence due to the temperature change of the lens LP is noticeable, and the focus is excessive. It shifts in the over direction.

  Further, in a region exceeding the upper limit of the conditional expression (1), the negative refractive power becomes excessively large with respect to the positive refractive power, so that the influence due to the temperature change of the lens LN is prominent and the focus is excessive. Will shift to the under direction.

Regarding conditional expression (1), more preferably -0.52 <fn / fp ≦ −0.32 (1a)
It is desirable to satisfy.

  At least one of the lenses having one or more negative refractive powers is included in the foremost first lens group.

  In each embodiment, the first lens unit L1 uses plastic as a material for a lens having an aspheric shape and having a negative refractive power. This is because a lens made of a plastic material having a negative refractive power is used in the first lens unit L1 that requires a strong negative refractive power, which is a characteristic of a wide-angle type (retrofocus type) lens system having a long back focus. Aberrations are corrected efficiently.

  In addition, since the first lens unit L1 has a larger aperture than the other lens units, the density of the light beam at the time of projection is reduced, and accordingly, it becomes easy to set an aspheric shape that can appropriately correct the light beam. Thus, the burden of correcting aberrations of other lenses is reduced, and the number of lenses is effectively reduced.

◎ When the focal length of the entire system at the zoom position at the wide angle end is fw −7 <fn / fw <−1 (2)
Is satisfied.

  Conditional expression (2) is a conditional expression in which the refractive power of the lens LN having a negative refractive power made of a plastic material and having an aspherical shape is properly defined with respect to the focal length of the entire lens system. In a region exceeding the lower limit of conditional expression (2), the refractive power of the lens LN becomes loose. Then, for example, in the configuration having a strong negative refractive power in the front group peculiar to the retrofocus type, the action of the aspherical shape of the lens LN becomes insufficient. Further, in the region exceeding the upper limit, the negative refractive power of the lens NL becomes too strong, and the decentering sensitivity becomes excessively large, and it is difficult to make adjustments for obtaining the performance of the entire lens system.

  More preferably, the numerical range of conditional expression (2) is set as follows.

-5 <fn / fw <-2 (2a)
The first lens group closest to the magnification conjugate side is composed of lenses having a negative refractive power. Among these lenses, the lens on the most reduction conjugate side is a meniscus shape having a concave surface on the magnification conjugate side or a convex surface on the reduction conjugate side. Is made up of.

  In each embodiment, all the lenses in the first lens unit L1 are lenses having negative refractive power (preferably having at least one aspherical shape), and the surface on the enlargement conjugate side is concave or the surface on the reduction conjugate side. Is provided with a convex meniscus lens, thereby generating distortion aberration or aberration that is opposite to astigmatism generated by a lens having a convex surface on the magnification conjugate side, and distortion aberration generated in the first lens unit L1. Astigmatism is corrected with a small number of lenses. In addition, the effective diameter of the front lens is reduced.

◎ When the average Abbe number of the negative refractive power lens material in the first lens group is ν1n 47 <ν1n (3)
Is satisfied.

  Conditional expression (3) is a conditional expression for reducing the lateral chromatic aberration generated in the first lens unit L1. By using a material with small chromatic dispersion as the material of the negative refractive power lens of the first lens unit L1, the lateral chromatic aberration is suppressed to a low level. In a region exceeding the lower limit of conditional expression (3), the lateral chromatic aberration is increased, which is not good.

  More preferably, the numerical value of conditional expression (3) should be set as follows.

50 <ν1n (3a)
Next, features of each embodiment will be described.

  In Example 1 of FIG. 1, in the first lens unit L1, in order from the magnification conjugate side to the reduction conjugate side, the magnification conjugate side surface is convex and the meniscus lens G11 having a negative refractive power, and the magnification conjugate side surface is convex. Thus, the lens G12 having a negative meniscus power and the surfaces of the magnification conjugate side and the reduction conjugate side are constituted by a concave lens G13.

  The lens G12 is made of a plastic material, and the surfaces on the enlargement conjugate side and the reduction conjugate side are aspherical. Distortion is mainly corrected by making the surfaces of the magnification conjugate side and the reduction conjugate side of the lens G12 into aspherical shapes.

  Further, distortion and astigmatism are corrected by the surface on the reduction conjugate side of the lens G13, and chromatic aberration of magnification is obtained by using low dispersion glass (Abbe number of 54 or more) as the material of all the lenses of the first lens unit L1. Occurrence is reduced.

  The second lens unit L2 is composed of a lens G21 having a convex conjugate side and a reduction conjugate side, and mainly corrects various aberrations generated in the first lens unit L1. The lens G21 is made of a glass material having a high refractive index (1.75 or more), thereby reducing the Petzval sum and reducing variations in various aberrations such as spherical aberration during zooming.

  Further, the Petzval sum is reduced to reduce the field curvature and astigmatism at an intermediate image height, thereby obtaining a high resolving power. Further, from the viewpoint of correcting chromatic aberration, a glass having a high refractive index and low dispersion characteristics is used in order to efficiently correct the lateral chromatic aberration generated in the first lens unit L1.

  The third lens unit L3 is composed of two lenses, a lens G31 having a negative meniscus refractive power on the magnification conjugate side and a lens G32 having a convex shape on the magnification conjugate side and the reduction conjugate side. It plays a role in scaling. By adopting a two-lens configuration with negative and positive refractive power, the variation in lateral chromatic aberration is reduced in the variable magnification region while having a large aperture.

  Further, the coma flare and the longitudinal chromatic aberration are corrected well. The aperture stop ST exists in the third lens unit L3 and moves together with the third lens unit L3 during zooming to suppress fluctuations in off-axis aberrations during zooming.

  The fourth lens unit L4 includes a lens G41 having a concave surface on the enlargement side. A strong negative refracting power is given to the lens G41 to correct the movement of the focus surface accompanying zooming. By arranging this lens G41 having a strong negative refractive power, the Petzval sum is efficiently reduced.

  The fifth lens unit L5 includes a lens G51 having concave surfaces on the enlargement conjugate side and a reduction conjugate side, a lens G52 having convex surfaces on the enlargement conjugate side and the reduction conjugate side, and a meniscus shape having a convex surface on the reduction conjugate side. The lens G53 has a positive refractive power.

  The Petzval sum is efficiently reduced by disposing a lens G51 having a strong negative refractive power on the enlargement conjugate side (screen side). In addition, the rear principal point position is controlled to ensure good telecentricity and to obtain the required back focus length.

  For the lens G52, low dispersion glass is used to suppress chromatic aberration. Further, plastic is used for the material of the lens G53 closest to the reduction conjugate side, and the surfaces on the enlargement conjugate side and the reduction conjugate side are aspherical. This lens G53 efficiently corrects off-axis aberrations such as astigmatism.

  The sixth lens unit L6 includes a lens G61 having a positive refractive power and a convex conjugated side surface. This lens G61 is used to maintain good telecentricity.

  In the first embodiment, the lenses G12 and G53 having positive and negative refractive power are made of plastic and one or more surfaces are aspherical. However, the present invention is not limited to this, and a plurality of lenses are made of a plastic material, and one or more surfaces are aspherical. It is also possible to correct the variation in optical performance such as a focus shift due to environmental changes. The lens having an aspherical shape is not limited to plastic, and may be made of a glass material. Alternatively, a hybrid aspherical shape may be used because a thin resin layer is formed on the lens surface to form an aspherical shape.

  The zoom lens of Example 1 has a small F-number of 1.7 and realizes a high-magnification projection lens with a zoom magnification of about 1.6 times while being capable of projecting a 100-type lens at a short distance of about 2.5 m. is doing.

  In Example 2 of FIG. 3, the first lens unit L1 includes three lenses G11, G12, and G13. Among these, the lenses G11 and G12 are the same as those in the first embodiment.

  The lens G13 is a lens having a negative refracting power having a meniscus shape with a convex surface of a reduction conjugate type. The lens G13 has a meniscus shape to correct distortion and astigmatism.

  The second to sixth lens groups L2 to L6 are the same as those in the first embodiment.

  In the zoom lens according to the second embodiment, a projection lens having a high zoom ratio of about 1.7 times while the F-number is as small as 1.75 and the 100 type can be projected at a short distance of about 2.4 m while the zoom magnification is about 1.7 times. Realized.

  In Example 3 of FIG. 5, the configuration of the first lens unit L1 and the second lens unit L2 is the same as that of Example 2.

  The third lens unit L3 includes a lens G31 having a convex conjugate side and a reduction conjugate side. By giving the lens G31 power (refractive power), it plays the role of the main variable power lens group. The aperture stop ST exists in the third lens unit L3, and moves together with the third lens unit L3 during zooming to suppress fluctuations in off-axis aberrations during zooming.

  The fourth lens unit L4 is composed of a negative meniscus lens G41 having a concave meniscus surface on the magnification conjugate side. A strong negative refracting power is given to the lens G41 to correct the movement of the focus surface accompanying zooming. By arranging this lens G41 having a strong negative refractive power, the Petzval sum is efficiently reduced.

  The fifth and sixth lens groups L5 and L6 are the same as those in the first embodiment.

  The zoom lens according to the third embodiment realizes a projection lens that has a small F number of 1.75 and can project a 100-type lens at a short distance of about 2.4 m.

  In Example 4 of FIG. 7, the configuration of the first, second, and third lens groups L1, L2, and L3 is the same as that of Example 3.

  The fourth lens unit L4 is composed of a lens G41 having negative refractive power whose concave and conjugate surfaces are concave. A strong negative refracting power is given to the lens G41 to correct the movement of the focus surface accompanying zooming. By arranging this lens G41 having a strong negative refractive power, the Petzval sum is efficiently reduced. In addition, the rear principal point position is controlled to ensure good telecentricity and to obtain the required back focus length.

  The fifth lens unit L5 includes a positive-refractive-power lens G51 having a convex surface on the enlargement conjugate side and a reduction-conjugate side, and a meniscus lens having a positive refractive power having a convex surface on the reduction-conjugate side. The lens G51 uses low-dispersion glass (for example, SFSL5, SFPL51 (both manufactured by OHARA)) and suppresses the deterioration of chromatic aberration to a smaller extent.

  Further, the lens G52 is made of a plastic material, and the surfaces on the enlargement conjugate side and the reduction conjugate side are aspherical. This lens G52 efficiently corrects off-axis aberrations such as astigmatism.

  The sixth lens group is the same as in the first embodiment. The zoom lens of Example 4 has a small F-number of 1.7 and can project a 100-type lens at a short distance of about 2.8 m while realizing a highly variable projection lens with a zoom magnification of about 1.5 times. is doing.

  The fifth embodiment shown in FIG. 9 differs from the first to fourth embodiments in that the zoom lens includes five groups as a whole. In the fifth embodiment, the configuration of the first and second lens groups L1 and L2 is the same as that of the third embodiment.

  The third lens unit L3 includes a meniscus lens G31 having a positive refractive power having a convex surface on the magnification conjugate side. By giving the lens G31 strong power, it plays the role of the main variable power lens group. The aperture stop ST exists in the third lens unit L3 and moves together with the third lens unit L3 during zooming, and suppresses fluctuations in off-axis aberrations during zooming.

  The fourth lens unit L4 includes a negative-refractive-power lens G41 whose concave and concave conjugate surfaces are concave, a positive-refractive-power lens G42 whose convex and negative conjugate-side surfaces are convex, and a reduced conjugate. The lens has a convex side surface and a meniscus lens G43 having a positive refractive power.

  The Petzval sum is efficiently reduced by arranging the lens G41 having a strong negative refractive power on the most conjugated side. In addition, the rear principal point position is controlled to ensure good telecentricity and to obtain the required back focus length. The lens G42 uses low dispersion glass as a material in order to suppress chromatic aberration.

  Further, the lens G43 closest to the reduction conjugate side is made of a plastic material, and the surfaces on the enlargement conjugate side and the reduction conjugate side are aspherical. This lens G43 efficiently corrects off-axis aberrations such as astigmatism. The fifth lens unit L5 includes a lens G51 having a positive refractive power and a convex conjugate side and a reduction conjugate side. The lens G51 maintains the telecentricity well.

  In Example 5, the lenses G12 and G43 having positive and negative refractive power are made of plastic and one or more surfaces are aspherical. However, the present invention is not limited to this, and a plurality of lenses are made of plastic and one or more surfaces are aspherical. Then, a change in optical performance such as a focus shift due to an environmental change may be corrected.

  The lens having an aspherical shape is not limited to plastic, and may be made of a glass material. Further, a hybrid type aspherical shape may be used because a thin resin layer is formed on the lens surface to form an aspherical shape.

  The zoom lens of Example 5 has a small F-number of 1.6 and realizes a projection lens capable of projecting a 100-type lens at a short distance of about 3.3 m.

  As described above, according to each embodiment, a long aperture with a large aperture, good telecentric performance on the reduction side, high resolution, low distortion, and good correction of lateral chromatic aberration in the visible light broadband. A zoom lens having a focus can be realized.

  Numerical examples 1 to 5 respectively corresponding to the numerical data of the zoom lenses of Examples 1 to 5 are shown below. In each numerical example, i indicates the order of optical surfaces from the enlargement side (front side), Ri is the radius of curvature of the i-th optical surface (i-th surface), and di is the i-th surface and the (i + 1) -th surface. , Ni and νi represent the refractive index and Abbe number of the material of the i-th optical member with respect to the d-line, respectively. f is a focal length, and Fno is an F number.

  In addition, two surfaces on the most reducing side of Numerical Examples 1 to 4 and five surfaces on the most reducing side of Numerical Example 5 are surfaces constituting a glass block GB corresponding to a color synthesis prism, a face plate, various filters, and the like. It is.

  Further, when k is a conic constant, A, B, C, D, and E are aspheric coefficients, and the displacement in the optical axis direction at the position of the height h from the optical axis is x with respect to the surface vertex, the aspheric surface The shape is

Is displayed. Where r is the paraxial radius of curvature. For example, the display of “e-Z” means “10 ^−Z ”.

  Table 1 shows the relationship between the above-described conditional expressions 1 to 3 and various numerical values in the numerical examples 1 to 5.

  FIG. 11 is a schematic view of a main part of an embodiment in which the zoom lens of the present invention is applied to a reflective liquid crystal projector (image projection apparatus).

  The light beam emitted from the illuminating means 101 is reflected by the beam splitter 102, is incident on the reflective liquid crystal display panel 103 and is reflected, and the light beam which has been light-modulated by the liquid crystal display panel 103 passes through the beam splitter 102 and zooms. The light enters the lens 104, and image information based on the liquid crystal display panel 103 is projected onto the screen 105 by the zoom lens 104.

  In this embodiment, a transmissive liquid crystal display panel may be used as the liquid crystal display panel 103.

  FIG. 12 is a schematic diagram of a main part of an embodiment in which the zoom lens of the present invention is applied to an imaging apparatus. In the present embodiment, an example in which the zoom lens described above is used as a photographing lens in an imaging apparatus such as a video camera, a film camera, or a digital camera is shown. In FIG. 8, the image of the subject 9 is formed on the photoconductor 7 by the zoom lens 8 to obtain image information.

Schematic diagram of a main part of an image projection apparatus using the zoom lens of Example 1. Aberration diagram when the object distance is 1.7 m when the zoom lens of Numerical Example 1 is expressed in mm. Schematic diagram of main parts of an image projection apparatus using the zoom lens of Example 2. Aberration diagram at the object distance of 1.7 m when the zoom lens of Numerical Example 2 is expressed in mm. Schematic diagram of main parts of an image projection apparatus using the zoom lens of Example 3 Aberration diagram at the object distance of 1.7 m when the zoom lens of Numerical Example 3 is expressed in mm. Schematic diagram of main parts of an image projection apparatus using a zoom lens according to Embodiment 4 Aberration diagram at the object distance of 1.7 m when the zoom lens of Numerical Example 4 is expressed in mm. Schematic view of main parts of an image projection apparatus using the zoom lens of Example 5. Aberration diagram when the object distance is 2.3 m when the zoom lens of Numerical Example 5 is expressed in mm. Schematic diagram of the main part when the image projection device is applied to a reflective liquid crystal projector Schematic diagram of main parts of an embodiment of an imaging apparatus

Explanation of symbols

L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L5 5th lens group L6 6th lens group LCD Liquid crystal display element (image surface)
GB glass block (color synthesis prism)
S Sagittal image plane collapse M Meridional image plane collapse SP screen ASP Aspherical surface ST Aperture

Claims (11)

In order from the front to the rear, the first lens group having a negative refractive power that does not move due to zooming, the second lens group having a positive refractive power, the third lens group having a positive refractive power, and a fourth lens having a negative refractive power. A lens unit, a fifth lens unit having a positive refractive power, and a sixth lens unit having a positive refractive power that does not move due to zooming. During zooming from the wide-angle end to the telephoto end, A zoom lens in which 5 lens groups move independently forward ,
A positive lens made of a plastic material and having at least one front or rear aspherical surface;
It is made of a plastic material, and at least one front or rear surface has an aspherical negative lens,
The focal length of the positive lens made of the i-th plastic material included in the zoom lens is fpi,
The focal length of the negative lens made of the jth plastic material included in the zoom lens is fni,
age,

-0.56 <fn / fp ≦ −0.32
A zoom lens characterized by satisfying The first lens group consists only of lenses with negative refractive power,
A negative lens with a convex front surface,
2. The zoom lens according to claim 1, further comprising a negative lens having a convex rear surface. 3. The zoom lens according to claim 1, wherein at least one of the aspherical positive lenses is included in the fifth lens group. 47 <ν1n, where ν1n is the average Abbe number of the negative refractive power lens material in the first lens group
The zoom lens according to claim 2, wherein: -7 <fn / fw <-1 where fw is the focal length of the entire system at the zoom position at the wide-angle end
The zoom lens according to claim 1, wherein the zoom lens satisfies the following. In order from the front to the rear, the first lens group having a negative refractive power that does not move for zooming, the second lens group having a positive refractive power, the third lens group having a positive refractive power, and a fourth lens having a positive refractive power. The lens group is composed of a fifth lens group having a positive refractive power that does not move due to zooming, and the second to fourth lens groups independently move forward during zooming from the wide-angle end to the telephoto end. A zoom lens that
A positive lens made of a plastic material and having at least one front or rear aspherical surface;
It is made of a plastic material, and at least one front or rear surface has an aspherical negative lens,
The focal length of the positive lens made of the i-th plastic material included in the zoom lens is fpi,
The focal length of the negative lens made of the jth plastic material included in the zoom lens is fni,
age,

-0.56 <fn / fp ≦ −0.32
A zoom lens characterized by satisfying 7. The zoom lens according to claim 6, wherein at least one of the aspherical positive lenses is included in the fourth lens group. 47 <ν1n, where ν1n is the average Abbe number of the negative refractive power lens material in the first lens group
The zoom lens according to claim 6 or 7, wherein: -7 <fn / fw <-1 where fw is the focal length of the entire system at the zoom position at the wide-angle end
The zoom lens according to claim 6, wherein the zoom lens satisfies the following. An image projection apparatus that projects a projected image original image on a screen surface using the zoom lens according to claim 1. 10. An optical apparatus characterized in that image information is formed on an imaging means surface using the zoom lens according to any one of claims 1 to 9.