JP2005321744A - Small-sized three-group zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a lens system compact at the photographing and collapsing time while favorably maintaining high resolution of the lens system in a small-sized three-group zoom lens whose variable power ratio is threefold or more. <P>SOLUTION: The lens system is composed of three groups of lenses which are negative, positive, and positive in order from an object side. When varying the power, a 1st group G<SB>1</SB>is moved to relatively approach to a 2nd group G<SB>2</SB>, and this G<SB>2</SB>is monotonously moved to the object side, and a 3rd lens group G<SB>3</SB>is moved so that the moving locus is a convex arc to the object side. The G<SB>3</SB>is moved to the object side at the time of focusing. Moreover, the G<SB>1</SB>consists of, in order from the object side, a negative 1st lens L<SB>1</SB>facing a concave surface of a large curvature to the image side and a positive meniscus form 2nd lens L<SB>2</SB>of which at least one surface is made aspherical and the convex surface of a large curvature is faced to the object side. Moreover, the lens system satisfies the conditional expressions (1) and (2); 2.0<¾f<SB>1</SB>¾/f<SB>W</SB><2.6 (1), 0.41<F<SB>2</SB>/f<SB>3</SB><0.50 (2), however, f<SB>W</SB>represents a focal length of the whole system at the wide angle end, and f<SB>1</SB>represents a focal length of the 1st lens group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zoom lens having a three-group structure for reading an image formed on an image sensor such as a CCD or a CMOS. Specifically, the zoom lens is preferably used for a digital camera or a video camera and has a zoom ratio of 3 times. It relates to a small three-group zoom lens.

  In recent years, digital cameras, which are rapidly spreading, use a three-group zoom lens for compactness and good aberration correction. In particular, a rear focus type three-group zoom lens that extends the final group during focusing. Are frequently used (see, for example, Patent Documents 1 and 2 below).

  The three-group zoom lens described in Patent Document 1 below includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power and having an aperture stop, and a positive refractive power. When a zooming operation is performed from the wide-angle end to the telephoto end, the first lens unit is moved toward the image side and then reversed and moved toward the object side. As a result, the movement locus is moved so as to form a convex arc shape on the image side, the second lens group is moved monotonously to the object side, and the third lens group is moved to the object side and then reversed to the image side. It is configured to move so that the movement trajectory has a convex arc shape on the object side.

  The three-group zoom lens described in Patent Document 2 below includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. The third lens unit moves monotonically on the image plane side or has a convex arc shape on the image plane side while focusing on an object at infinity when zooming from the wide-angle end to the telephoto end. It is configured to move while drawing the trajectory.

JP-A-10-307258 JP 2001-296476 A

  However, digital cameras have made remarkable progress over the past few years, and demands for smaller lens systems, higher zoom ratios, and higher resolution have become stricter year by year.

Under such a requirement, in the one described in Patent Document 1, the focal length of the first lens group is about 2.8 to 3.6 times the absolute value of the focal length of the entire lens system at the wide angle end. Yes, when the zoom ratio is 3 times or more, it is difficult to achieve compactness of the entire lens length.
On the other hand, in the lens described in Patent Document 2, as described above, at the time of zooming, the third lens group moves so as to draw a convex arc-like locus on the image surface side or monotonously on the image surface side. If the zoom ratio is 3 times or more, it becomes difficult to correct field curvature at an intermediate magnification.

  In addition, in terms of downsizing the lens system, it is desirable that the lens length is small when the lens system is retracted into the camera body in addition to the compact length of the lens at the time of shooting. For that purpose, it is particularly necessary to reduce the thickness of the first lens group and to reduce the number of the first lens group. However, when the resolution of the peripheral angle of view is taken into consideration, an aspheric lens It is important that the lens is composed of two lenses including

  In that respect, in the configuration described in Patent Document 2, the configuration of the first lens group includes a negative lens having one aspherical surface with a concave surface having a large curvature facing the image side and a spherical surface on both sides in order from the object side. The above condition is satisfied for the time being. However, the negative lens on the object side is composed of an aspherical glass lens, and an aspherical surface is formed on the image-side surface which is a concave surface having a large curvature, as described in each example of Patent Document 2, in particular. In this case, it is difficult to reduce the lens center thickness due to glass molding problems, and it is difficult to achieve further compactness.

  The present invention has been made in view of the above-described circumstances, and in a small three-group zoom lens having a zoom ratio exceeding 3 times, the lens system is made compact at the time of photographing and retracting while achieving high resolution of the lens system. An object of the present invention is to provide a small three-group zoom lens capable of achieving the above.

The small three-group zoom lens of the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power and a diaphragm for adjusting the amount of light, and a positive refractive power A third lens group having
When zooming from the wide-angle end to the telephoto end, the first lens group is moved so as to be relatively close to the second lens group, and the second lens group is moved monotonously to the object side. The third lens group is moved so that the movement locus becomes a convex arc shape on the object side by reversing and moving toward the image side after moving to the object side,
In a compact three-group zoom lens in which the third lens group is moved toward the object side when focusing from infinity to a short distance,
The first lens group includes, in order from the object side, a negative lens having a concave surface facing the image side and a positive lens having a convex surface facing the object side and having an aspheric surface on at least one surface. It is what.

In addition to the above configuration, the small three-group zoom lens according to the present invention preferably satisfies the following conditional expressions (1) and (2).
2.0 <| f ₁ | / f _w <2.6 (1)
0.41 <f ₂ / f ₃ <0.50 (2)
However,
f _w : Focal length of the entire system at the wide angle end f ₁ : Focal length of the first lens group f ₂ : Focal length of the second lens group f ₃ : Focal length of the third lens group

  The second lens group includes a cemented lens of a biconvex lens and a lens having a negative refractive power with a concave surface facing the object side, and a single lens having at least one aspherical surface and a positive refractive power. Are preferably arranged in this order from the object side.

  Further, the positive lens in the first lens group is composed of a composite lens formed by bonding a glass lens and a resin material having a thickness smaller than that of the glass lens, and the positive lens in the side not bonded to the glass lens. The surface of the resin material is preferably an aspheric surface.

  In addition, it is preferable that the negative lens and the positive lens in the first lens group are configured to contact each other directly or via a predetermined parallel member at the periphery of each lens.

  In addition, it is preferable that the cemented lens and the single lens in the second lens group are configured to contact each other directly or via a predetermined parallel member at the periphery of each lens.

  The third lens group is preferably set so that the position at the wide-angle end is closer to the object side than the position at the telephoto end when the object distance is infinity.

  According to the small three-group zoom lens of the present invention, the first lens group has, in order from the object side, a two-lens configuration including a negative lens having a concave surface on the image side and a positive lens having a convex surface on the object side. At least one surface of the positive lens located on the image side has an aspheric surface. This reduces the thickness of the lens system in a state where the lens system is retracted into the camera body, while maintaining the resolution of the peripheral angle of view favorably and minimizing the number of lenses in the first lens group. One condition is satisfied.

  In addition, since the aspherical surface is provided not on the most object-side negative lens but on the positive lens located on the image side of this negative lens, glass molding has become an obstacle to reducing the lens thickness in the prior art. There is no room for the above problems. Therefore, the thickness of each lens constituting the first lens group, particularly the thickness of the negative lens located closest to the object side can be reduced, and not only the total lens length at the time of shooting but also the lens system is retracted into the camera body. It is possible to further reduce the thickness in the applied state.

  Furthermore, according to the small three-group zoom lens of the present invention, when the zooming ratio exceeds three times, the third lens group is moved so as to draw a convex arc-like locus on the object side during zooming. Even at an intermediate magnification that is difficult to correct, the field curvature can be corrected well.

  Further, when focusing from infinity to a short distance, the third lens unit is moved toward the object side to reduce the amount of movement of the third lens unit, particularly during focusing at the telephoto end. The system can be made compact.

Hereinafter, a representative embodiment of a small three-group zoom lens according to the present invention will be described with reference to Example 1 shown in FIG.
FIG. 1 shows the lens configuration of a small three-group zoom lens according to Example 1 of the present invention, in which the upper diagram is a lens configuration diagram at the wide-angle end, and the lower diagram is a lens configuration diagram at the telephoto end. The middle row shows the movement locus of each lens unit from the wide-angle end to the telephoto end.

As shown in FIG. 1, the small three-group zoom lens according to the embodiment of the present invention includes, in order from the object side, a first lens group G ₁ having a negative refractive power, a positive refractive power, and a light amount adjusting lens. A second lens group G ₂ having a diaphragm 2 and a third lens group G ₃ having a positive refractive power are disposed.

Further, when zooming from the wide-angle end to the telephoto end, each lens group is moved as follows. That is, the first lens group G ₁ is moved to draw an arc-like locus on the image side by moving to the image side and then reverse and moving toward the object side, and the second lens group G ₂ is moved. monotonically move toward the object side, the third lens group G ₃ is moved so as to draw a convex arcuate locus toward the object side by inverted after moving toward the object side is moved toward the image side. Thus, conventionally, when the zoom ratio exceeds 3 times, even in the intermediate magnification correction is difficult for curvature of field becomes under, that the movement locus of the third lens group G ₃ and the convex arcuate movement of the object side Thus, it can be corrected satisfactorily.
Incidentally, so that the first lens group G ₁ and the second lens group G ₂ moves closer to relatively monotonous.

Further, when the object distance infinity, and the object side than the position of the position of the third lens group G ₃ at the wide-angle end at the telephoto end. Further, when the focusing toward infinity to a close, moving the third lens group G ₃ toward the object side. Thus, at the time of zooming and focusing, it is possible to reduce the amount of movement of the third lens group G _3.
By moving the three lens groups G ₁ , G ₂ , and G ₃ along the optical axis X as described above, the focal length f of the entire system can be changed and the light beam can be efficiently focused on the imaging surface. .

Between the sixth lens L ₆ and the image plane (CCD imaging surface) filter unit 1 including a low pass filter or an infrared cut filter is arranged.

The first lens group G ₁ includes, in order from the object side, a first lens L ₁ having a negative refractive power with a concave surface having a large curvature directed to the image side, and at least one surface is aspherical and has an object side. The second lens L ₂ having a meniscus shape having a positive refractive power and a convex surface having a large curvature (a compound lens formed by cementing the second lens L ₂ and the third lens L _{3 in} Example 2).

By the first lens group G ₁ with such a configuration, it has been an obstacle to reduce the lens thickness in the prior art, without causing problems in molding the aspherical negative lens of glass, the image It is possible to satisfactorily correct surface curvature, distortion, and the like. Therefore, while achieving high resolution, the thickness of the lenses constituting the first lens group G _1, especially if, it is possible to reduce the thickness of the negative lens located at the most object side, only the total lens length at the time of shooting Therefore, it is possible to further reduce the thickness in a state where the lens system is retracted into the camera body.

The second lens group G ₂ includes a fourth lens L ₄ and a third lens L _{3 (in} the second embodiment the fourth lens L ₄₎ on both sides concave negative lens consisting of a positive lens of both side convex surface _(Example 2 Then, the lens is composed of three lenses, a cemented lens with the fifth lens L ₅ ) and a fifth lens L ₅ (sixth lens L ₆ in the second embodiment) consisting of a single lens, and the fifth lens L ₅ is at least 1 Since the positive lens having two aspheric surfaces can correct spherical aberration satisfactorily, it is possible to reduce the thickness of the entire lens system and the thickness of the retracted lens while achieving high resolution.

In addition, by being in contact through the negative lens in the first lens group G ₁ and (L ₁₎ a positive lens (L ₂₎ are in contact with the periphery of the lens, or the parallel members, the first lens group G it is possible to reduce _a thickness, also can reduce the lens eccentricity of the first lens group G _1.

Further, as described above, the second lens group G ₂ is composed of a cemented lens of a positive lens (L ₃ ) on both sides convex and a negative lens (L ₄ ) on both sides and a single lens (L ₅ ). Since the single lens (L ₅ ) has at least one aspherical surface and can correct spherical aberration well, the entire lens system and the thickness when retracted are reduced while achieving high resolution. be able to.

Further, the cemented lens (L ₃ , L ₄ ) and the single lens (L ₅ ) in the second lens group G ₂ are in contact with each other at the lens peripheral part or through a parallel member, so that the second lens can reduce the thickness of the group G _2, also can reduce the lens decentering of the second lens group G _2.
The third lens group _{G 3} is composed of a sixth lens _{L 6} (seventh lens _{L 7} in the second embodiment).

  Each aspheric surface is represented by the following aspheric expression.

  In the present embodiment, the aspherical shape using not only the conventional low-order even-order terms but also the odd-order terms, against the background of social circumstances such as the recent demand for higher resolution for optical systems and improved computer performance, etc. Is stipulated.

  In this way, by using an aspheric coefficient including odd-order terms, the parameters for determining the aspheric shape increase, so that the shape of the central region including the optical axis of the aspheric surface and the peripheral region are independent of each other. Therefore, both the central region and the peripheral region can be formed in a shape capable of satisfactorily correcting aberrations.

The small three-group zoom lens according to the present embodiment preferably satisfies the following conditional expressions (1) and (2).
2.0 <| f ₁ | / f _w <2.6 (1)
0.41 <f ₂ / f ₃ <0.50 (2)
However,
f _w : Focal length of the entire system at the wide angle end f ₁ : Focal length of the first lens group f ₂ : Focal length of the second lens group f ₃ : Focal length of the third lens group

Next, the technical significance of conditional expressions (1) and (2) will be described.
Conditional expression (1) defines the ratio | f ₁ | / f _w of the absolute value | f ₁ | of the focal length of the first lens group G ₁ and the focal length f _w of the entire system at the wide angle end. This is a conditional expression for satisfactorily correcting field curvature while achieving compactness.
In this condition (1), _| f 1 | when the value of _/ f _w exceeds the lower limit, although it is possible to downsize it is difficult to satisfactorily correct field curvature. On the other hand, | f 1 _| when the value of _/ f _w exceeds the upper limit, although it is possible to effectively correct field curvature becomes difficult to achieve compactness.

Condition (2), by defining the focal length _{f 2} of the second lens _{L 2} to the value of the ratio _f 2 / _{f 3} a focal length _{f 3} of the third lens _{L 3,} the spherical aberration while achieving downsizing And a conditional expression for favorably correcting curvature of field.
In this conditional expression (2), if the value of f ₂ / f ₃ exceeds the lower limit, it is possible to reduce the size, but the refractive power of the second lens group G ₂ increases, the spherical aberration deteriorates, and the image plane The curvature expands. On the other hand, if the value of f ₂ / f ₃ exceeds the upper limit, the refractive power of the second lens group G ₂ becomes small, and it is possible to satisfactorily correct spherical aberration and field curvature, but it is difficult to achieve compactness. It becomes.

<Example 1>
Hereinafter, a specific configuration of the small three-group zoom lens according to the present invention will be described with reference to Example 1.

That is, in the small three-group zoom lens according to Example 1, the first lens group G ₁ has, in order from the object side, a first lens L ₁ having a negative meniscus shape with a concave surface having a large curvature toward the image side, and and a second lens L ₂ having a positive meniscus shape with a large convex curvature on the object side. Further, both surfaces of the second lens L ₂ is a non-spherical surface represented by the above aspheric formula having a value in both of the even-order terms and the odd-order terms. The first lens L ₁ and the second lens L _2, is configured to directly contact with each other in each of the lens periphery.

The second lens group G ₂ includes, in order from the object side, a stop 2, a biconvex third lens L ₃ , a fourth lens L ₄ having a biconcave shape with a concave surface having a large curvature on the image side, and an object side. It consists of a fifth lens L ₅ having a positive meniscus shape with a convex surface, and the third lens L ₃ and the fourth lens L ₄ are cemented lenses. Further, both surfaces of the fifth lens L ₅ is an aspheric surface represented by the above aspheric formula having a value in both of the even-order terms and the odd-order terms.
The third lens group _{G 3} is composed of a sixth lens _{L 6} biconvex.

Numerical values relating to the small three-group zoom lens according to Example 1 are shown in Tables 1 to 3 below.
Table 1 shows the curvature radius R (mm) of each lens surface, the center thickness of each lens, and the air spacing between the lenses (hereinafter collectively referred to as the axial top surface spacing) D (mm), the d-line of each lens. Shows the values of the refractive index N and the Abbe number ν.
The numbers in the table indicate the order from the object side.
Also, the top of Table 1, the focal length f at the wide-angle end and the telephoto end each position (mm), indicating the value of F _NO and the angle 2 [omega.

Table 2 shows the constants KA, A3, A4, A5, A6, A7, A8, A9 of the aspheric formula (in the present embodiment, n is 10) for each of the aspheric surfaces. , A10 values are shown.
Further, in the upper part of Table 3, D ₄ (d1) at the wide angle end (f = 6.6 mm), the intermediate position (f = 11.7 mm) and the telephoto end (f = 20.8 mm) in the column of the shaft upper surface distance D described above, Each value of D ₁₀ (d2) and D ₁₂ (d3) is shown. The lower part of Table 3 shows values corresponding to the conditional expressions (1) and (2) described above in the present example.

  In the present embodiment, all the conditional expressions (1) and (2) described above are satisfied.

  FIG. 2 shows various aberrations (spherical aberration, astigmatism) at the wide-angle end (f = 6.6 mm), the intermediate position (f = 11.7 mm), and the telephoto end (f = 20.8 mm) of the small three-group zoom lens according to Example 1 above. It is an aberration diagram showing aberration, distortion and lateral chromatic aberration). Each spherical aberration diagram shows aberrations at 615 nm, 587.6 nm, and 460 nm, and each astigmatism diagram shows aberrations with respect to the sagittal image surface and the tangential image surface. As can be seen from FIG. 2, the small three-group zoom lens according to Example 1 can satisfactorily correct aberrations over the entire zoom region.

<Example 2>
Next, a small three-unit zoom lens according to Example 2 of the present invention will be described.

That is, as shown in FIG. 3, a small three-unit zoom lens according to Example 2, pertaining to the first embodiment and has been substantially the same configuration, in place of the second lens L ₂ of Example 1 , of the second lens L ₂ and the thin made of glass (made of a resin material) plastic that it uses a third lens L ₃ is bonded to become a composite aspherical lens made of a lens, and, of the composite aspherical lens the object-side surface (a surface of the second lens L ₂ on the object side) is spherical (the image side surface of the third lens L ₃₎ image-side surface is different in that it is an aspherical surface.

  Thus, the aspherical surface is a composite aspherical lens in which a glass lens and a thin plastic lens are joined, and the surface of the plastic lens not joined to the glass lens is aspherical. Since it is composed of a spherical surface, the degree of freedom in selecting a glass lens glass material can be increased compared to the case where an aspherical surface is formed on the surface of a glass lens, and the chromatic aberration of magnification can be reduced at a low cost by selecting an appropriate glass material. Can be reduced. Further, the chromatic aberration of magnification can be further reduced by utilizing the difference in dispersion between the glass lens and the plastic lens.

  In other words, it is possible to alleviate the problem that the change in the optical characteristics due to the temperature change in the plastic lens is large while reducing the manufacturing difficulty and high cost when forming the aspherical surface on the glass lens.

Numerical values relating to the small three-group zoom lens according to Example 2 are shown in Tables 4 to 6 below.
Table 4 shows the values of the curvature radius R (mm) of each lens surface, the axial top surface distance D (mm) of each lens, and the refractive index N and the Abbe number ν in the d-line of each lens.
The numbers in the table indicate the order from the object side.
Also, the top of Table 4, the focal length f at the wide-angle end and the telephoto end each position (mm), indicating the value of F _NO and the angle 2 [omega.

  Table 5 shows the constants KA, A3, A4, A5, A6, A7, A8, A9 of the aspheric formula (in the present embodiment, n is 16) for each of the aspheric surfaces. , A10, A11, A12, A13, A14, A15, and A16 are shown. However, the constants A11 to A16 are set to 0 for the aspheric surfaces of the tenth surface and the eleventh surface.

  That is, each aspheric surface of the second embodiment can also be expressed by the above aspheric formula, and the aspheric coefficient is configured to have values in both the even-order terms and the odd-order terms as in the first embodiment. . However, the aspherical surface (fifth surface) on the image side of the above compound lens is configured to use the third to sixteenth higher order terms as the aspheric coefficient. In this way, by using higher-order aspherical coefficients including odd-order terms, the parameters that determine the aspherical shape further increase, so that both the central region and the peripheral region are formed into shapes that can perform better aberration correction. It becomes possible to do.

Further, in the upper part of Table 6, D ₅ (d1) at the wide angle end (f = 6.6 mm), the intermediate position (f = 11.7 mm) and the telephoto end (f = 20.8 mm) in the column of the shaft upper surface distance D described above, Each value of D ₁₁ (d2) and D ₁₃ (d3) is shown. The lower part of Table 6 shows values corresponding to the conditional expressions (1) and (2) described above in the present example.

  In the present embodiment, all the conditional expressions (1) and (2) described above are satisfied.

  FIG. 4 shows various aberrations (spherical aberration, astigmatism) at the wide-angle end (f = 6.6 mm), the intermediate position (f = 11.7 mm), and the telephoto end (f = 20.8 mm) of the small three-group zoom lens according to Example 2 above. It is an aberration diagram showing aberration, distortion and lateral chromatic aberration). Each spherical aberration diagram shows aberrations at 615 nm, 587.6 nm, and 460 nm, and each astigmatism diagram shows aberrations with respect to the sagittal image surface and the tangential image surface. As can be seen from FIG. 4, the small three-group zoom lens according to Example 2 can satisfactorily correct aberrations over the entire zoom region.

  Note that the small three-group zoom lens of the present invention is not limited to the above-described embodiment, and various other modes can be changed. For example, the aspherical surface of the aspherical lens disposed in the second lens group in each of the above embodiments may be provided on any one surface. In the composite aspheric lens of Example 2, the object-side surface of the composite aspheric lens can also be an aspheric surface.

FIG. 3 is a lens configuration diagram of a small three-group zoom lens according to Example 1 of the present invention. FIG. 5 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end, the intermediate position, and the telephoto end of the small three-unit zoom lens according to Example 1 of the present invention. Lens configuration diagram of a small three-group zoom lens according to Example 2 of the present invention Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion and lateral chromatic aberration) at the wide-angle end, intermediate position and telephoto end of the small three-group zoom lens according to Example 2 of the present invention.

Explanation of symbols

1 filter section 2 aperture G ₁ ~G ₃ lens group L ₁ ~L ₇ lens R ₁ to R ₁₅ lens surfaces such as D ₁ to D ₁₄ axial distance X optical axis

Claims (7)

In order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power and a diaphragm for adjusting the amount of light, and a third lens group having positive refractive power are disposed. And
When zooming from the wide-angle end to the telephoto end, the first lens group is moved so as to be relatively close to the second lens group, and the second lens group is moved monotonously to the object side. The third lens group is moved so that the movement locus becomes a convex arc shape on the object side by reversing and moving toward the image side after moving to the object side,
In a compact three-group zoom lens in which the third lens group is moved toward the object side when focusing from infinity to a short distance,
The first lens group includes, in order from the object side, a negative lens having a concave surface facing the image side and a positive lens having a convex surface facing the object side and having an aspheric surface on at least one surface. A small three-group zoom lens. 2. The compact three-unit zoom lens according to claim 1, wherein the following conditional expressions (1) and (2) are satisfied.
2.0 <| f ₁ | / f _w <2.6 (1)
0.41 <f ₂ / f ₃ <0.50 (2)
However,
f _w : Focal length of the entire system at the wide-angle end f ₁ : Focal length of the first lens group f ₂ : Focal length of the second lens group f ₃ : Focal length of the third lens group   The second lens group includes a cemented lens of a biconvex lens and a lens having negative refractive power with a concave surface facing the object side, and a single lens having at least one aspherical surface and having positive refractive power, 3. The small three-group zoom lens according to claim 1, wherein the zoom lens is disposed in this order from the object side.   The positive lens in the first lens group is composed of a composite lens formed by bonding a glass lens and a resin material having a thickness smaller than that of the glass lens, and the resin material on the side not bonded to the glass lens The small three-group zoom lens according to any one of claims 1 to 3, wherein the surface is an aspherical surface.   The negative lens and the positive lens in the first lens group are configured to contact each other directly or via a predetermined parallel member at the periphery of each lens. 4. A small three-group zoom lens according to claim 1.   2. The cemented lens and the single lens in the second lens group are configured to contact each other directly or via a predetermined parallel member at the periphery of each lens. The small three-group zoom lens according to any one of 5.   The third lens group is set so that the position at the wide-angle end is closer to the object side than the position at the telephoto end when the object distance is infinity. A small three-group zoom lens according to any one of the preceding claims.

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