JP4182089B2 - Zoom lens and optical apparatus having the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens and an optical apparatus having the zoom lens, and particularly to a video camera, an electronic still camera, and a silver lens that have a high zoom ratio, a large aperture ratio, and reduce the size of the entire lens system while maintaining good optical performance. This is suitable for a salt photo camera.

  Recently, with the reduction in size and weight of home video cameras and the like, remarkable progress has been made in reducing the size of zoom lenses for imaging, particularly in reducing the overall lens length, reducing the front lens diameter, and simplifying the configuration. It has been poured.

  As one means for achieving these objects, a so-called rear focus type zoom lens is known in which focusing is performed by moving a lens group other than the first lens group on the object side.

  In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens that moves the first lens group to perform focusing, thereby facilitating downsizing of the entire lens system, and close-up photography. In particular, close-up photography is facilitated, and the small and lightweight lens group is moved, so that the driving force of the lens group is small and rapid focusing is possible.

  As such a rear focus type zoom lens, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power. The fourth lens group has four lens groups, and the second lens group is moved to perform zooming, and the fourth lens group is moved to correct and focus the image plane variation accompanying zooming. Are known (Patent Documents 1 and 2).

  Further, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a positive refractive power. The fifth lens group has five lens groups, and the second lens group is moved to perform zooming, and the fourth lens group is moved to correct and focus the image plane variation accompanying zooming. Is known (Patent Document 3).

  In these zoom lenses, axial chromatic aberration and lateral chromatic aberration are particularly large on the telephoto side, and it becomes particularly noticeable when it is used for a high pixel and high image quality such as a digital still camera.

  In order to deal with this problem, in order from the object side, in a zoom lens having a four-group configuration of positive, negative, positive, and positive refractive power, a lens made of an anomalous dispersion glass material is used for the first lens group. Known (Patent Document 4).

  On the other hand, as a method for suppressing the occurrence of chromatic aberration, a proposal has recently been made to apply a diffractive optical element to an imaging optical system (Patent Documents 5 to 10).

  In Patent Documents 5 and 6, chromatic aberration is reduced by applying a diffractive optical element to a single lens.

  Patent Document 7 proposes to use a diffractive optical element for the second lens group or the third lens group of the zoom lens, and achieves a reduction in the number of lenses and a reduction in the size of the lens system compared to the conventional example.

  In Patent Documents 8 and 9, a reduction in the number of lenses in the first lens group is achieved by providing a diffractive optical surface in the first lens group.

  Further, in Patent Document 10, a diffractive optical surface is provided on the cemented lens surface (bonding surface) of two lenses to reduce chromatic aberration.

In addition, when a diffractive optical element is used in an imaging system, it is necessary to obtain sufficient diffraction efficiency over the entire visible range. In general, in a single-layer diffraction grating, diffraction efficiency decreases at wavelengths other than the design wavelength, and unnecessary diffracted light other than the design order causes color flare. In view of this, it is known that high diffraction efficiency is obtained over the entire visible range by optimally selecting three different materials and two different grating thicknesses for each diffraction grating constituting the diffractive optical element. (Patent Document 11).
JP-A-62-24213 JP-A-63-247316 JP-A-8-5913 JP 2000-267005 A JP-A-4-213421 JP-A-6-324262 US Pat. No. 5,268,790 Japanese Patent Laid-Open No. 11-52238 JP-A-11-52244 Japanese Patent Laid-Open No. 11-305126 JP-A-9-127322

  In general, in a zoom lens having a high zoom ratio with a zoom ratio of about 10 times, when an attempt is made to correct chromatic aberration by introducing a diffractive optical surface into the first lens group, the angle of light incident on the diffractive optical surface depends on the angle of view and the focus. Since it changes greatly with the change in distance, the diffraction efficiency changes and the amount of unnecessary diffracted light increases. In the examples of Patent Documents 8 and 9, since the diffractive optical surface is provided on the lens surface convex on the image side, the difference in angle between the axial light beam and the peripheral light beam entering the diffractive optical surface is large, and sufficient diffraction efficiency is obtained. I can't.

  In order to obtain high diffraction efficiency over the entire visible range, the diffractive optical element needs to be composed of a plurality of diffraction gratings, and it is necessary to set a diffractive optical surface on a bonded lens surface having lenses before and after. In Patent Document 10, the diffraction grating is provided on the bonded lens surface, but the incident condition on the diffraction grating is not considered.

  In view of these conventional techniques, an object of the present invention is to provide a zoom lens having a novel configuration having high optical performance in the entire zoom range and an optical apparatus having the zoom lens.

The zoom lens according to the first aspect of the present invention includes, in order from the object side, a first lens group having a positive refractive power that does not move for zooming, a second lens group having a negative refractive power that moves in the optical axis direction during zooming, and zooming. In the zoom lens having only the four lens groups, that is, the third lens group that does not move for zooming and the fourth lens group having a positive refractive power that moves in the optical axis direction during zooming, the first lens group is located on the object side. And a diffractive optical part composed of a diffraction grating is provided on the bonding surface, the radius of curvature of the bonding surface is RD, and the focal length of the first lens group is When f1
0.5 <RD / f1 <1.2
It is characterized by satisfying the following conditions.

  A second aspect of the invention is characterized in that, in the first aspect of the invention, the diffractive optical part is constituted by a laminated structure of a plurality of diffraction gratings made of materials having different dispersions.

  A third aspect of the invention is characterized in that, in the first or second aspect of the invention, the bonding surface is a bonding surface of a bonding lens including a negative lens and a positive lens in order from the object side.

A zoom lens according to a fourth aspect of the invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power that moves in the optical axis direction during zooming, and a first lens group that does not move for zooming. In a zoom lens having only three lens groups, and four lens groups of a fourth lens group having a positive refractive power that moves in the optical axis direction during zooming,
The first lens group includes, in order from the object side, a cemented lens composed of a negative meniscus lens having a convex surface facing the object side and a positive lens, and a diffraction grating composed of a diffraction grating on the cemented surface of the cemented lens. When an optical part is provided, the radius of curvature of the bonding surface is RD, and the focal length of the first lens group is f1,
0.5 <RD / f1 <1.2
It is characterized by satisfying the following conditions.

The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the phase given to the wavefront by the diffractive optical part is λd and the distance from the optical axis is h.
φ (h) = (2π / λd) · (C ₂ · h ² + C ₄ · h ⁴ + ·· C _{2 · i} · h ^{2 · i} )
When the focal length at the telephoto end of the entire system is ft and the F number at the telephoto end is FnoT,
−0.01 <C ₂ · (ft / FnoT) <0
It is characterized by satisfying the following conditions.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the diffractive optical unit has the highest diffraction efficiency with respect to a light beam incident at an incident angle of 3 degrees to 10 degrees. It is a feature.

  The invention of claim 7 is the invention of any one of claims 1 to 6, wherein the diffractive optical part is composed of one or more diffraction gratings, and one of the diffraction gratings goes from the central part to the peripheral part. It is characterized by having a region where the lattice height changes.

  The invention of claim 8 is the invention of any one of claims 1 to 7, wherein the focal length of the first lens group is f1, and the focal lengths at the wide-angle end and the telephoto end of the entire system are fw and fT, respectively. and when,

It is characterized by satisfying the following conditions.

The invention of claim 9 is the invention of any one of claims 1 to 8, wherein the third lens group is movable so as to have a component in a direction perpendicular to the optical axis in order to stabilize the image. Yes, when the magnification of the third lens group for the object at the telephoto end and at infinity is β3, and the magnification of the optical system on the image side from the third lens group is βr,
0.5 <| (1-β3) · βr | <3
It is characterized by satisfying the following conditions.

  The invention of claim 10 is characterized in that in the invention of any one of claims 1 to 9, an image is formed on the photoelectric conversion element.

  A camera according to an eleventh aspect of the invention includes the zoom lens according to any one of the first to tenth aspects and a photoelectric conversion element that receives an image formed by the zoom lens.

  According to the present invention, it is possible to achieve a zoom lens having high optical performance in the entire zoom range and an optical apparatus having the same.

Specifically, FIG. 1 is a cross-sectional view of a main part of a zoom lens of Numerical Example 1 corresponding to Embodiment 1, and FIGS. 2, 3, and 4 are wide-angle end, intermediate, and telephoto of the zoom lens of Numerical Example 1. It is an aberration diagram in each zoom position of the end. FIG. 5 is a cross-sectional view of the main part of the zoom lens of Reference Numerical Example 1 corresponding to Reference Example 1, and FIGS. 6, 7, and 8 are the wide-angle end, intermediate, and telephoto ends of the zoom lens of Reference Numerical Example 1, respectively. It is an aberration diagram in the zoom position. 9 is a cross-sectional view of the main part of the zoom lens of Reference Numerical Example 2 corresponding to Reference Example 2. FIGS. 10, 11, and 12 are diagrams of the zoom lens of Reference Numerical Example 2 at the wide-angle end, the middle, and the telephoto end, respectively. It is an aberration diagram in the zoom position. FIG. 13 is a schematic view of an optical apparatus using the zoom lens according to the present invention corresponding to the second embodiment.
(Embodiment 1)
In the lens cross-sectional view shown in FIG. 1, L1 is a first lens unit having a positive refractive power (optical power = reciprocal of focal length) that does not move for zooming, and L2 is in the optical axis direction during zooming. The second lens unit having a negative refractive power that moves to L, and the third lens unit having a positive refractive power that does not move for zooming (L3), and L4 moves in the optical axis direction during zooming and focusing. This is a fourth lens unit having a positive refractive power.

  SP is an aperture stop, which is disposed in front of the third lens unit L3. G is a glass block corresponding to a color separation prism, a face plate, a filter, or the like. IP is an image plane, on which a solid-state imaging device (photoelectric conversion device) such as a CCD or CMOS is disposed. FP is a flare cut stop.

  During zooming from the wide-angle end to the telephoto end, as shown by the arrow in FIG. 1, the second lens unit L2 is moved to the image side to perform main magnification, and the fourth lens unit L4 is convex toward the object side. The movement of the image plane is corrected by correcting the fluctuation of the image plane position due to zooming.

  Further, the solid line curve 4a and the dotted line curve 4b of the fourth lens unit L4 shown in FIG. 1 indicate image plane fluctuations accompanying zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. The movement locus | trajectory for correct | amending is shown. In this way, by moving the fourth lens unit L4 so as to have a convex locus on the object side, the space between the third lens unit L3 and the fourth lens unit L4 is effectively used, and the total lens length is shortened. Has been achieved effectively.

  In the first embodiment, for example, focusing from an infinitely distant object to a close object at the telephoto end is performed by extending the fourth lens unit L4 forward as indicated by a straight line 4c in FIG.

  The wide-angle end and the telephoto end refer to zoom positions when the second lens unit L2, which is a variable power lens unit, is positioned at both ends of a range in which the mechanism can move in the optical axis direction. The same applies to other zoom lens embodiments described later.

  In the first embodiment, the first lens unit L1 and the third lens unit L3 are fixed during zooming and focusing, but may be moved as necessary. In addition, by moving the third lens unit L3 so as to have a component in a direction perpendicular to the optical axis, it is possible to stabilize (anti-vibration) the blur of a captured image caused by camera shake or the like.

  In the first embodiment, the first lens unit L1 is made up of, in order from the object side, a cemented lens including a negative meniscus lens G1 and a positive lens G2 having a convex surface facing the object side, and a convex surface having a strong refractive power on the object side compared to the image side. And a positive meniscus lens G3 facing the lens. A diffractive optical part composed of a diffraction grating rotationally symmetric with respect to the optical axis is provided on the bonding surface of the lenses G1 and G2, and the bonded lens is used as a diffractive optical element. By appropriately setting the curvature of the bonding surface provided with this diffractive optical part, the angle of the incident light beam to the diffractive optical part (diffractive optical surface) of the light beam based on each angle of view is within a range of ± 15 degrees. In this way, high diffraction efficiency is maintained over the entire zoom range and the entire angle of view.

  Here, the configuration of the diffractive optical element used in Embodiment 1 will be described.

  FIG. 14 is a partially enlarged sectional view of a diffractive optical part of the diffractive optical element 1, and a diffraction grating 3 composed of one layer is provided on a substrate (transparent substrate) 2. FIG. 15 is a diagram showing the characteristics of the diffraction efficiency of the diffractive optical element 1. In FIG. 15, the horizontal axis represents the wavelength, and the vertical axis represents the diffraction efficiency. Note that the diffraction efficiency is the ratio of the amount of diffracted light to the total transmitted light beam, and the reflected light at the lattice boundary is not considered here because the explanation is complicated.

The optical material of the diffraction grating 3 is an ultraviolet curable resin (refractive index n _d = 1.513, Abbe number ν _d = 51.0), the grating thickness d ₁ is set to 1.03 μm, the wavelength is 530 nm, and the + 1st order. The diffraction efficiency of the diffracted light is maximized. That is, the design order is + 1st order and the design wavelength is 530 nm. In FIG. 15, the diffraction efficiency of the + 1st order diffracted light is indicated by a solid line.

  Further, FIG. 15 also shows diffraction efficiency of diffraction orders in the vicinity of the design order (0th order and + 2nd order which are + 1st order ± 1st order). As can be seen from the figure, the diffraction efficiency at the design order is highest near the design wavelength, and gradually decreases at other wavelengths.

  The decrease in diffraction efficiency at this design order becomes diffracted light of other orders, which causes flare. Further, when the diffractive optical element is used at a plurality of locations in the optical system, a decrease in diffraction efficiency at a wavelength other than the design wavelength leads to a decrease in transmittance.

  Next, a laminated diffractive optical element in which a plurality of diffraction gratings made of different materials are laminated will be described. FIG. 16 is a partially enlarged cross-sectional view of a laminated diffractive optical element, and FIG. 17 is a diagram showing the wavelength dependence of the diffraction efficiency of + 1st order diffracted light of the diffractive optical element shown in FIG. In the diffractive optical element shown in FIG. 16, a first diffraction grating 104 made of an ultraviolet curable resin (refractive index nd = 1.499, Abbe number νd = 54) is formed on a substrate 102, and a second diffraction grating is formed thereon. 105 (refractive index nd = 1.598, Abbe number νd = 28). In this combination of materials, the grating thickness d1 of the first diffraction grating 104 is d1 = 13.8 μm, and the grating thickness d2 of the second diffraction grating 105 is d2 = 10.5 μm.

  As can be seen from FIG. 17, by using a diffractive optical element provided with a diffraction grating having a laminated structure, a high diffraction efficiency of 95% or more is obtained in the entire range of wavelengths used (in this case, the visible region) in the diffracted light of the designed order. Yes.

  The diffractive optical element having the above-described laminated structure is not limited to the material that constitutes the diffraction grating, but other plastic materials may be used. Depending on the substrate, the first layer may be directly You may form in a base material. Further, the lattice thicknesses are not necessarily different, and the lattice thicknesses of the two layers 104 and 105 may be equal depending on the combination of materials. In this case, since the lattice shape is not formed on the surface, it is excellent in dust resistance and can improve the assembling workability of the diffractive optical element. Furthermore, the two diffraction gratings 104 and 105 are not necessarily in close contact with each other, and two diffraction grating layers may be arranged with an air layer therebetween.

  In the case of the first embodiment, the substrates 2 and 102 in FIGS. 14 and 16 are used as at least one lens constituting the bonded lens, and a diffraction grating is provided on the lens surface. For example, as shown in FIG. 14, when the diffraction grating is a single layer, a diffraction grating may be provided on one lens surface. When the diffraction grating is a multilayer of two or more layers, the diffraction grating is provided on both lens surfaces. What is necessary is just to adhere | attach in a peripheral part (outside an effective diameter), aligning.

  In this embodiment, the bonding surface on which the diffractive optical unit is provided is a spherical surface. However, if the base surface on which the diffraction grating is provided is an aspherical surface, spherical aberration and coma at the telephoto end can be further corrected. Can also be done.

  The configuration of these diffractive optical units is the same in Reference Examples 1 and 2 described later.

As described above, since the diffractive optical part is composed of at least one phase type diffraction grating, the diffractive optical part actually has a predetermined thickness, but the thickness is negligible in terms of geometrical optics. When the thickness is ignored, it may be called a diffractive optical surface (diffractive surface).
(Reference Example 1)
In the lens cross-sectional view shown in FIG. 5, L1 is a first lens unit having a positive refractive power that does not move for zooming (fixed), and L2 is a second lens having a negative refractive power that moves in the optical axis direction during zooming. A third lens group having a positive refractive power that does not move for zooming, and a fourth lens group having a negative refractive power that moves in the optical axis direction during zooming and focusing; L5 is a fifth lens unit having a positive refractive power that does not move for zooming (fixed).

  SP is an aperture stop, G is a face plate, a glass block corresponding to a filter, etc., and IP is an image plane.

  During zooming from the wide-angle end to the telephoto end, as shown by the arrow in FIG. 5, the second lens unit L2 is moved to the image side to perform main magnification, and the fourth lens unit L4 is convex toward the image side. The movement of the image plane is corrected by correcting the fluctuation of the image plane position due to zooming.

  Further, the solid line curve 4a and the dotted line curve 4b of the fourth lens unit L4 shown in FIG. 5 indicate image plane fluctuations accompanying zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. The movement locus | trajectory for correct | amending is shown. Thus, by moving the fourth lens unit L4 so as to have a convex locus on the image side, the space between the fourth lens unit L4 and the fifth lens unit L5 is effectively used, and the total lens length is shortened. Has been achieved effectively.

  In Reference Example 1, for example, focusing from an infinitely distant object to a close object at the telephoto end is performed by retracting the fourth lens unit L4 rearward as indicated by a straight line 4c in FIG.

  In Reference Example 1, the first lens group, the third lens group, and the fifth lens group are fixed during zooming and focusing, but may be moved as necessary. In addition, by moving the third lens unit L3 so as to have a component in a direction perpendicular to the optical axis, it is possible to stabilize the blur of the captured image caused by camera shake or the like.

  In Reference Example 1, by adopting such a lens configuration, the change in focal length with respect to the movement of the second lens unit L2 on the wide angle side is positive, negative, positive, and positive refraction as shown in the first embodiment. Compared to a four-group zoom lens composed of four lens groups of power, the front lens effective diameter can be made smaller.

In Reference Example 1, the first lens unit L1 is a cemented lens composed of a negative meniscus lens G1 having a convex surface facing the object side and a positive lens G2 in order from the object side, and has a stronger refractive power on the object side than on the image side. The diffractive optical part is composed of a positive meniscus lens G3 having a convex surface, and a rotationally symmetric diffraction grating with respect to the optical axis is provided on the bonding surface of the lenses G1 and G2. Then, by appropriately setting the curvature of the bonding surface provided with the diffractive optical part, the angle of the incident light beam to the diffractive optical part based on each angle of view is within a range of ± 15 degrees. High diffraction efficiency is maintained over the entire zoom range and the entire angle of view.
(Reference Example 2)
In the lens cross-sectional view shown in FIG. 9, L1 is a first lens unit having a positive refractive power that does not move for zooming (fixed), and L2 is a second lens having a negative refractive power that moves in the optical axis direction during zooming. The lens group, L3 is a third lens group having a positive refractive power that does not move for zooming (fixed), L4 is a fourth lens group having a negative refractive power that moves in the optical axis direction during zooming, and L5 is a light beam during zooming. It is the 5th lens group of the positive refractive power which moves to an axial direction.

  SP is a diaphragm, G is a glass block corresponding to a face plate, a filter, etc., and IP is an image plane.

  During zooming from the wide-angle end to the telephoto end, as shown by the arrows in FIG. 9, the second lens unit L2 is on the image side, the fourth lens unit L4 is on the image side, and the fifth lens unit is convex. L5 is moved along a convex locus toward the object side.

  In addition, a rear focus type is employed in which the fifth lens unit L5 is moved in the optical axis direction to perform focusing. In the present embodiment, the first lens unit L1 and the third lens unit L3 are fixed during zooming, but may be moved as necessary.

  The solid line curve 5a and the dotted line curve 5b of the fifth lens unit L5 shown in FIG. 9 show the image plane variation accompanying zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. A movement trajectory for correction is shown.

  In Reference Example 2, for example, focusing from an infinitely distant object to a close object at the telephoto end is performed by extending the fifth lens unit L5 forward as indicated by a straight line 5c in FIG.

  In Reference Example 2, the first lens group and the third lens group are fixed during zooming and focusing, but may be moved as necessary. In addition, by moving the third lens unit L3 so as to have a component in a direction perpendicular to the optical axis, it is possible to stabilize the blur of the captured image caused by camera shake or the like.

  In Reference Example 2, by adopting such a lens configuration, the change in focal length with respect to the movement of the second lens unit L2 on the wide angle side is positive, negative, positive, and positive refraction as shown in the first embodiment. Compared to a four-group zoom lens composed of four lens groups of power, the front lens effective diameter can be made smaller. Further, by moving the three lens groups during zooming, better optical performance is achieved over the entire zoom range.

  In Reference Example 2, the first lens unit L1 is a cemented lens composed of a negative meniscus lens G1 and a positive lens G2 with convex surfaces facing the object side in order from the object side, and a convex surface having a stronger refractive power on the object side than the image surface side. And a diffractive optical element formed of a diffraction grating rotationally symmetric with respect to the optical axis is provided on the bonding surface of the lens G1 and the lens G2.

  In the zoom lenses shown in Embodiment 1 and Reference Examples 1 and 2, the first lens group is composed of a negative meniscus lens and a positive lens, and a positive meniscus lens having a convex surface facing the object side. By providing a diffractive optical part on the bonding surface and appropriately setting the phase it gives to the transmitted wavefront, the chromatic aberration generated in the first lens group is reduced, and the chromatic aberration is corrected well over the entire zooming range. I have to.

  For example, even if the first lens group is composed of only positive lenses and a diffractive optical element is provided in the first lens group, the chromatic aberration can be suppressed when considering chromatic aberrations of only two wavelengths such as d-line and g-line. it can. However, since the diffractive optical surface has a large anomalous dispersion, the chromatic aberration for the other wavelengths, that is, the so-called secondary spectrum becomes large, especially at the telephoto end, and the chromatic aberration cannot be corrected within the entire visible wavelength range. .

  Therefore, in the present invention, the chromatic aberration including the secondary spectrum at the telephoto end is corrected well by combining the refractive achromatic condition and the achromatic condition of the diffractive optical surface optimally to obtain high optical performance. Yes.

  In order to share the achromatic effect of the first lens group with the diffractive optical surface, it is desirable that the optical power by diffraction has a positive value. If the optical power of the diffractive optical surface becomes a negative value, the direction of chromatic aberration generated will be the same as that of a normal refractive optical system, and the achromatic effect due to the diffractive optical surface will not appear, and the entire optical system will This is because sufficient correction of chromatic aberration cannot be performed.

  In general, in a zoom lens having a high zoom ratio of about 10 times or more, the angle of light rays incident on the first lens group varies greatly depending on the zoom position and angle of view. When the angle of the incident light beam on the diffractive optical surface varies, the diffraction efficiency is lowered, causing color flare. Therefore, in the zoom lenses shown in the embodiment and Reference Examples 1 and 2, the position of the lens surface on which the diffractive optical unit is provided and the radius of curvature thereof are set to appropriate values, and each lens group is appropriately set to set the entire zoom range. High diffraction efficiency is obtained at all angles of view.

  FIG. 19 shows the variation of the incident angle with respect to the height from the optical axis in the diffractive optical surface of Embodiment 1 (Numerical Example 1). The horizontal axis is the height from the optical axis, and the vertical axis is the incident angle. The area within the shaded area is the distribution range of incident light.

  In FIG. 19, when the shape of the diffraction grating is set so that the diffraction efficiency is maximized with respect to a light beam having an incident angle of 0 degrees, the height of the diffractive optical surface is near +19 degrees with respect to the set incident angle. A light beam having a difference in degree is incident. On the other hand, when the shape of the diffraction grating is set so that the diffraction efficiency is maximized with respect to a light beam having an incident angle on the diffractive optical surface of about 9 degrees, about ± 11 degrees with respect to the set incident angle. The fluctuation of the incident angle can be suppressed within the range. Considering the decrease in diffraction efficiency, it is desirable that the variation of the incident angle on the diffractive optical surface is within ± 15 degrees.

  Therefore, in the first embodiment and the reference examples 1 and 2, the diffractive optical system has the highest diffraction efficiency with respect to a light beam incident at a wavelength of 590 nm, a desired order, and a predetermined incident angle between 3 degrees and 10 degrees. The shape of the diffraction grating constituting the part is optimized. As a result, necessary and sufficient diffraction efficiency is obtained over the entire zoom range.

  Furthermore, by dividing the region of the diffractive optical part and changing the assumed incident angle on the diffractive optical surface in the central region and the peripheral region, for example, and optimizing the diffraction grating shape for each region, the variation in the incident angle on the diffractive optical surface It is possible to further suppress the decrease in diffraction efficiency due to. In particular, in the zoom lenses shown in Embodiment 1 and Reference Examples 1 and 2, it is preferable to set the grating thickness in the peripheral region to be thinner than the central region.

  As is clear from Embodiment 1 and Reference Examples 1 and 2, the zoom lens according to the present invention includes, in order from the object side, a first lens unit having a positive refractive power that does not move for zooming, and light during zooming. It has a basic configuration including a second lens unit having a negative refractive power that moves in the axial direction.

The present invention is broadly divided into first and second inventions. Of these, the first invention is characterized in that the first lens group has a convex bonding surface on the object side, and a diffractive optical part having a diffraction grating is provided on the bonding surface.

In the second invention, the first lens unit has a cemented lens composed of a negative meniscus lens having a convex surface facing the object side and a positive lens in order from the object side, and diffracted on the cemented surface of the cemented lens. A diffractive optical part having a grating is provided. At the same time, when the radius of curvature of the bonding surface is RD and the focal length of the first lens group is f1,
0.5 <RD / f1 <1.2 (1)
It is characterized by satisfying the following conditions.

  In the first invention, one or more of the following conditions should be satisfied.

  (A-1) The diffractive optical part is constituted by a laminated structure of a plurality of diffraction gratings made of materials having different dispersions.

(A-2) When the radius of curvature of the bonding surface provided with the diffractive optical part is RD and the focal length of the first lens group is f1,
0.5 <RD / f1 <1.2 (1) is satisfied.

  (A-3) The bonding surface on which the diffractive optical unit is provided is a bonding surface of a bonding lens including a negative lens and a positive lens in order from the object side.

  In the first and second inventions, it is preferable to satisfy one or more of the following conditions.

(A-1) The wavelength given to the wavefront by the diffractive optical unit is φ (h) = (2π / λd) · (C ₂ · h ² + C ₄ · h ⁴ + ・ ・ C ₂・_i・ h ²・ⁱ )
When the focal length at the telephoto end of the entire system is ft and the F number at the telephoto end is FnoT,
−0.01 <C ₂ · (ft / FnoT) <0 (2)
To satisfy the following conditions.

  (A-2) As in Embodiment 1 and Reference Examples 1 and 2, the third lens group that does not move for zooming is disposed on the image side of the second lens group.

  (A-3) As in Embodiment 1 and Reference Examples 1 and 2, the third lens group does not move for zooming on the image side of the second lens group, and moves in the optical axis direction for zooming. The fourth lens group having a positive refractive power is arranged.

  (A-4) As in Reference Examples 1 and 2, a third lens group that does not move for zooming on the image side of the second lens group, and a negative refractive power that moves in the optical axis direction during zooming. That is, four lens groups are arranged.

  (I-5) As in Reference Examples 1 and 2, the third lens group that does not move for zooming on the image side of the second lens group, and the negative refractive power that moves in the optical axis direction during zooming. 4 lens groups and a fifth lens group having a positive refractive power are arranged.

  (A-6) The diffractive optical part is composed of one or more diffraction gratings, and one of these diffraction gratings has a region in which the grating height changes from the central part to the peripheral part.

  Hereinafter, the incident angle of the light beam to the diffractive optical unit refers to the incident angle with respect to the lens surface provided with the diffraction grating, the incident angle with respect to the grating surface of the diffraction grating, or the incident angle with respect to the diffractive optical surface described above.

  (A-7) In the diffraction order in which the diffraction efficiency of the diffractive optical part is the highest, the incident angle of the light having a wavelength of 590 nm to the diffractive optical part in which the diffraction efficiency is the highest is in the range of 3 degrees to 10 degrees. is there.

  (A-8) When the focal length of the first lens unit is f1, and the focal lengths at the wide-angle end and the telephoto end of the entire system are fw and fT, respectively.

To satisfy the following conditions.

(A-9) A third lens group that does not move to the image side of the second lens group for zooming but moves so as to have a component in a direction perpendicular to the optical axis for image stabilization, and zooming In this case, at least one lens unit that moves in the optical axis direction is arranged, the magnification of the third lens unit for the telephoto end and the object at infinity is β3, and the magnification of the optical system on the image side from the third lens unit is βr. and when,
0.5 <| (1-β3) · βr | <3 (4)
To satisfy the following conditions.

  (A-10) The third lens group is moved so as to have a component in a direction perpendicular to the optical axis to displace the image, thereby stabilizing the blur of the photographed image caused by camera shake or the like.

  Next, the technical meaning of each conditional expression described above will be described.

  Conditional expression (1) is for reducing the fluctuation of the incident angle with respect to the diffractive optical part while introducing the diffractive optical part (diffractive optical surface) to the bonding surface in the first lens group. Here, the “incident angle with respect to the diffractive optical part” assumes an incident angle when the diffractive optical part is geometrically optically regarded as a diffractive optical surface, and in the numerical examples of each embodiment described later, diffractive optics. This means the angle of incidence on the optical surface (lens surface) on which the part is provided.

  If the curvature of the diffractive optical surface (bonding surface) exceeds the lower limit of conditional expression (1) and becomes too strong (large), the incident angle with respect to the axial ray at the telephoto end becomes too large and the diffraction efficiency decreases. It ’s not good. On the other hand, if the curvature exceeds the upper limit and the curvature becomes too weak (small), the incident angle becomes large around the wide angle side.

  More preferably, the numerical range of conditional expression (1) is set as follows.

0.6 <RD / f1 <1.0 (1a)
Conditional expression (2) is for appropriately setting the phase to the wavefront provided by the diffractive optical part, and thus for appropriately setting the shape of the diffraction grating constituting the diffractive optical part.

  If the lower limit of conditional expression (2) is exceeded, chromatic aberration correction in the diffractive optical unit becomes too large, and correction of chromatic aberration in the secondary spectrum becomes excessive, which is not good. Conversely, if the upper limit is exceeded, the chromatic aberration of the secondary spectrum will be undercorrected.

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

−0.005 <C2 · (ft / FnoT) <0 (2a)
Conditional expression (3) relates to the refractive power of the first lens group, and is to effectively obtain a desired zoom ratio while reducing aberration fluctuations accompanying zooming. When the refractive power of the first lens unit becomes too strong beyond the lower limit, it is advantageous for downsizing, but it becomes difficult to correct spherical aberration and coma generated at the telephoto end. On the other hand, if the upper limit is exceeded, the amount of movement of the second lens unit during zooming becomes too large and the overall lens length becomes long.

  More preferably, the numerical range of conditional expression (3) is set as follows.

  Conditional expression (4) relates to the imaging magnification of the third lens group. If the lower limit of conditional expression (4) is exceeded, the amount of movement of the third lens unit necessary for image stabilization will not be good. On the other hand, if the upper limit is exceeded, the sensitivity of the third lens group becomes too high, and control during image stabilization becomes difficult. More preferably, the numerical range of conditional expression (4) is set as follows.

0.8 <| (1-β3) · βr | <2.0 (4a)
Numerical Example 1 and Reference Numerical Examples 1 and 2 corresponding to the numerical data of the zoom lenses of Embodiment 1 and Reference Examples 1 and 2 are shown below. In each numerical example, i indicates the order of surfaces from the object side, Ri is the radius of curvature of the i-th surface from the object side, Di is the i-th and i + 1-th lens thickness or air spacing from the object side , Ni and νi are the refractive index and Abbe number of the i-th optical member. f, Fno, and 2ω represent the focal length, the F number, and the angle of view of the entire system when focusing on an object at infinity, respectively.

  The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, k is the eccentricity, and B, C, and D are aspherical coefficients, respectively. When

It is expressed by the following formula.

The diffractive optical surface (diffractive surface) is the aforementioned phase function,
This is expressed by giving a phase coefficient of φ (h) = (2π / λd) · (C ₂ · h ² + C ₄ · h ⁴ + ·· C ₂ · _i · h ² · ⁱ ).

Further, for example, the display of “e-Z” means “10 ^−z ”.

  Table 1 shows the relationship between the conditional expressions described above and the numerical values in the numerical examples.

(Embodiment 2)
Next, an embodiment of a video camera (optical apparatus) using a zoom lens as shown in Embodiment 1 and Reference Examples 1 and 2 as a photographing optical system will be described with reference to FIG.

  In FIG. 13, 10 is a video camera body, 11 is a photographing optical system constituted by any of the zoom lenses described in the first embodiment and Reference Examples 1 and 2, and 12 is a CCD for receiving a subject image by the photographing optical system 11. , CMOS, etc., a solid-state imaging device (photoelectric conversion device), 13 is a recording means for recording a subject image received by the imaging device 12, and 14 is a viewfinder for observing a subject image displayed on a display device (not shown). . The display element is constituted by a liquid crystal panel or the like, and a subject image formed on the imaging element 12 is displayed.

  Thus, by applying the zoom lens of the present invention to an optical apparatus such as a video camera, an optical apparatus having a small size and high optical performance can be realized.

Lens cross-sectional view at the wide-angle end of the zoom lens according to Numerical Example 1 Aberration diagram at the wide-angle end of the zoom lens according to Numerical Example 1 Aberration diagram at the intermediate zoom position of the zoom lens according to Numerical Example 1. Aberration diagram at the telephoto end of the zoom lens according to Numerical Example 1 Cross-sectional view of the zoom lens of Reference Numerical Example 1 at the wide-angle end Aberration diagram at the wide-angle end of the zoom lens of Reference Numerical Example 1 Aberration diagram at the intermediate zoom position of the zoom lens of the reference numerical value example 1 Aberration diagram at the telephoto end of the zoom lens of Reference Numerical Example 1 Cross-sectional view of the zoom lens of Reference Numerical Example 2 at the wide-angle end Aberration diagram at the wide-angle end of the zoom lens of Reference Numerical Example 2 Aberration diagram at the intermediate zoom position of the zoom lens of the reference numerical example 2 Aberration diagram at the telephoto end of the zoom lens of Reference Numerical Example 2 Sectional drawing of the principal part of the optical apparatus of the present invention Cross section of diffractive optical element with single layer structure Illustration of diffraction efficiency of a diffractive optical element with a single layer structure Cross-sectional view of a laminated diffractive optical element Illustration of diffraction efficiency of diffractive optical element with laminated structure Cross-sectional view of a laminated diffractive optical element The figure which shows the incident angle to the diffraction optical part of Numerical Example 1

Explanation of symbols

L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L5 5th lens group d d line g g line ΔM meridional image plane ΔS sagittal image plane SP aperture IP image plane G glass block

Claims (11)

In order from the object side, a first lens group having a positive refractive power that does not move for zooming, a second lens group having a negative refractive power that moves in the optical axis direction during zooming, a third lens group that does not move for zooming, In a zoom lens having only four lens units of a fourth lens unit having a positive refractive power moving in the optical axis direction during zooming as a lens unit, the first lens unit has a convex bonding surface on the object side. A diffractive optical part composed of a diffraction grating is provided on the bonding surface, the radius of curvature of the bonding surface is RD, and the focal length of the first lens group is f1,
0.5 <RD / f1 <1.2
A zoom lens characterized by satisfying the following conditions:   2. The zoom lens according to claim 1, wherein the diffractive optical part is constituted by a laminated structure of a plurality of diffraction gratings made of materials having different dispersions.   The zoom lens according to claim 1, wherein the bonding surface is a bonding surface of a bonding lens including a negative lens and a positive lens in order from the object side. In order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power that moves in the optical axis direction during zooming, a third lens group that does not move for zooming, and an optical axis direction during zooming In the zoom lens having only four lens groups of the fourth lens group having a positive refractive power moving to the lens group,
The first lens group includes, in order from the object side, a cemented lens composed of a negative meniscus lens having a convex surface facing the object side and a positive lens, and a diffraction grating composed of a diffraction grating on the cemented surface of the cemented lens. When an optical part is provided, the radius of curvature of the bonding surface is RD, and the focal length of the first lens group is f1,
0.5 <RD / f1 <1.2
A zoom lens characterized by satisfying the following conditions: Assuming that the wavelength of the d-line is λd and the distance from the optical axis is h, the phase given to the wavefront by the diffractive optical unit is
φ (h) = (2π / λd) · (C ₂ · h ² + C ₄ · h ⁴ + ·· C _{2 · i} · h ^{2 · i} )
When the focal length at the telephoto end of the entire system is ft and the F number at the telephoto end is FnoT,
−0.01 <C ₂ · (ft / FnoT) <0
The zoom lens according to claim 1, wherein the following condition is satisfied.   6. The zoom lens according to claim 1, wherein the diffractive optical unit has the highest diffraction efficiency with respect to a light ray incident at an incident angle of 3 degrees to 10 degrees.   The diffractive optical part is composed of one or more diffraction gratings, and one of the diffraction gratings has a region in which the grating height changes from the central part to the peripheral part. The zoom lens according to any one of 6. When the focal length of the first lens group is f1, and the focal lengths at the wide-angle end and the telephoto end of the entire system are fw and fT, respectively.
The zoom lens according to claim 1, wherein the following condition is satisfied. The third lens group is movable so as to have a component in a direction perpendicular to the optical axis in order to stabilize the image, and the magnification of the third lens group with respect to an object at infinity is β3, When the magnification of the optical system on the image side from the lens group is βr,
0.5 <| (1-β3) · βr | <3
The zoom lens according to claim 1, wherein the following condition is satisfied.   The zoom lens according to claim 1, wherein an image is formed on the photoelectric conversion element.   11. A camera comprising: the zoom lens according to claim 1; and a photoelectric conversion element that receives an image formed by the zoom lens.