JP2003098433A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact zoom lens easily applied to a device and also having high optical performance by fixing the entire length of the lens, and made optimum to be used in a digital video camera and a digital still camera and having a variable power ratio being about 3. SOLUTION: This zoom lens 1 is constituted of a 1st lens group GR1 having positive refractive power, always fixed positionally and consisting of a biconvex lens, a 2nd lens group GR2 having negative refractive power, capable of moving positionally and consisting of a concave meniscus lens whose convex surface faces the object side and a convex meniscus lens whose convex surface faces the object side, a 3rd lens group GR3 having positive refractive power, capable of moving positionally and consisting of at least one aspherical lens having positive refractive power and one lens having negative refractive power, and a 4th lens group GR4 having positive refractive power, capable of moving positionally and consisting of a biconvex lens in this order from the object side. Then, the power is varied by moving the 2nd and the 3rd lens groups at a fixed ratio while putting a diaphragm IR fixed positionally with respect to an imaging surface in between, and also the variation of an image point is corrected by moving the 4th lens group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a variable power ratio of about 3 which is optimal for use in digital video cameras and digital still cameras.

[0002]

2. Description of the Related Art As a conventional compact zoom lens having a zoom ratio of about 3 times for a digital video camera or a digital still camera, it is described in, for example, Japanese Patent Application Laid-Open Nos. 2001-33701 and 2001-33702. There was something that was done.

The former is a three-group seven-lens structure consisting of a first lens group having a negative refracting power, a second lens group having a positive refracting power, and a third lens group having a positive refracting power in order from the object side. The zoom lens of No. 1 is adapted to perform zooming by moving the first lens group and the second lens group.
In addition, the latter is the first having a negative refractive power in order from the object side.
A zoom lens having an eight-lens structure including a lens group, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, wherein the zoom lens is configured by moving the first lens group and the second lens group. It was designed to do doubles.

Incidentally, the zoom lenses described in the above two publications have the following problems.

That is, since the total lens length changes due to zooming, it is difficult to configure the entire apparatus when used in a digital camera or digital video camera. Also,
Since the diaphragm moves together with the second lens group, it causes an increase in size of the entire lens. Furthermore, the first
If the lens group has a negative refracting power, negative distortion becomes large at the wide-angle end, and if it is attempted to correct this, the number of lenses forming the first lens group will increase.

Further, as another example of a compact zoom lens having a zoom ratio of about 3 times for a conventional digital video camera or digital still camera, there is disclosed in Japanese Patent Laid-Open No. 2001-42219.
In the seven-lens configuration described in Japanese Patent Laid-Open Publication No. 1994-09, which includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. There is a telephoto type zoom lens in which three lens groups are independently moved to perform zooming.

In the zoom lens disclosed in Japanese Unexamined Patent Application Publication No. 2001-42219, as in the zoom lenses described in the above two publications, the total lens length changes due to zooming, so that the zoom lens can be used in digital cameras and digital video cameras. In addition to the problem that the configuration of the entire device is difficult to use and the configuration in which the diaphragm moves together with the second lens group, it causes the size of the entire lens to increase. There was another problem like. That is, it means that the distance of the exit pupil is short and it is not suitable for an apparatus using an image pickup device, and that it is impossible to make it bright because the F value is large.

Further, as another example of a compact zoom lens having a zoom ratio of about 3 times for a conventional digital video camera or digital still camera, as disclosed in Japanese Patent Laid-Open No. 10-62687, from the object side in order. 7 to 8 including a first lens group having a positive refractive power, a third lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. There is a single-lens zoom lens.

However, the above-mentioned Japanese Unexamined Patent Publication No. 10-6268.
The zoom lens disclosed in Japanese Patent Publication No. 7 is disadvantageous in terms of cost and heavy in weight because the second lens group having negative refracting power is composed of three lenses. There was a problem in that

[0010]

In view of the above problems, the present invention is applied to a digital video camera or a digital still camera which has a high optical performance while facilitating application to the apparatus by fixing the total lens length. An object of the present invention is to provide a compact zoom lens having a variable power ratio of about 3 which is optimum for the above.

[0011]

In order to solve the above-mentioned problems, according to the present invention, in order from the object side, a first lens group having a positive refracting power and a fixed position, and a negative refracting power are provided. A second lens group having a movable position, a third lens group having a positive refractive power and a movable position, and a third lens group having a positive refractive power and a movable position. In the zoom lens composed of four lens groups, each of the first to fourth lens groups is a biconvex lens, a concave meniscus lens having a convex surface facing the object side and a convex meniscus lens having a convex surface facing the object side, at least It is composed of one aspherical lens having a positive refractive power, one lens having a negative refractive power, and a biconvex lens, and the positions of the second lens group and the third lens group are fixed with respect to the imaging surface. Move it at a fixed ratio with the diaphragm Together to perform zooming by, and to correct the variation of the image point by moving the fourth lens group.

Therefore, the total length of the lens does not change, and it is possible to provide a compact zoom lens having high optical performance.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the zoom lens of the present invention will be described below with reference to the accompanying drawings.

First, the outline of the zoom lens of the present invention will be described.

The zoom lens of the present invention comprises, in order from the object side,
A first lens group GR1 having a positive refractive power and a fixed position at all times, a second lens group GR2 having a negative refractive power and a movable position, and a position having a positive refractive power Is composed of a third lens group GR3 that is movable, and a fourth lens group GR4 that has a positive refractive power and is movable in position.

The first lens group GR1 is composed of a biconvex lens, and the second lens group GR2 is composed of a concave meniscus lens having a convex surface facing the object side and a convex meniscus lens having a convex surface facing the object side. The third lens group GR3 is composed of at least one aspherical lens having a positive refractive power and one lens having a negative refractive power, and the fourth lens group GR3 is composed of a biconvex lens. It The second lens group GR2 and the third lens group GR3
A stop IR is provided between the first lens group GR4 and the image plane IMG, and a low-pass filter,
A filter FL including a cover glass of the image pickup device is provided.

In the zoom lens according to the present invention, the second lens group GR2 and the third lens group GR3 have an image pickup surface (image surface) IM.
Zooming is performed by moving the diaphragm IR whose position is fixed with respect to G at a constant ratio with the stop IR interposed therebetween, and by moving the fourth lens group GR4, fluctuation of the image point can be suppressed. It is supposed to be corrected.

The zoom lens according to the present invention has a νPL
When the Abbe number _GR2 at e-line of a lens having a positive refractive power second lens group GR2, it is preferable to configure so as to satisfy the νPL _GR2 <28 (condition 1). In the conditional expression 1, if νPL _{G R2} is 28 or more, the axial chromatic aberration at the telephoto end is overcorrected.

Further, nNL _GR2 is the second lens group GR2.
The refractive index at the e-line of a lens having a negative refractive power of n is preferably configured to satisfy nNL _GR2 > 1.8 (conditional expression 2).

In the conditional expression 2, when nNL _GR2 becomes 1.8 or less, the radius of curvature of the concave surface must be reduced, the Petzval sum tends to the negative side, and the image surface tends to be over. I will end up. In addition, negative distortion will increase at the wide-angle end.

In this case, it is desirable that the lens having the negative refractive power of the second lens group GR2 include an aspherical surface. This has the effect of shifting the image surface to the under side and the distortion aberration to the positive side for the purpose of correcting the aberration that occurs when the conditional expression 2 is satisfied.

Furthermore, if f ₂ is the focal length of the second lens group and f _w is the focal length at the wide-angle end of the entire lens system, then 2 <| f ₂ / f _w | <2.8 (conditional expression 3) It is desirable to configure so that

In the above conditional expression 3, when the value of | f ₂ / f _w | exceeds the lower limit value, the radius of curvature of the concave surface of the negative lens becomes small, the Petzval sum decreases, and the curvature of field at the time of zooming decreases. It becomes difficult to correct the change.

If the value of | f ₂ / f _w | exceeds the upper limit value, the amount of movement at the time of zooming becomes large, which is disadvantageous for downsizing. The coma becomes stronger. Furthermore, the ratio of the movement amount of the second lens group GR2 and the third lens group GR3 approaches 1: 1, the lens system of the third lens group GR3 becomes large, and the aberration correction of the positive lens to the aspherical surface is performed. The burden on you will increase. Specifically, the directions of spherical aberration and field curvature are opposite to each other, and a good balance between them cannot be obtained.

As described above, in the zoom lens of the present invention, the second lens group GR2 and the third lens group GR3, which sandwich the fixed aperture IR, move during zooming. The lens group GR2 and the third lens group GR3 are 2:
It is desirable to be configured to move at a ratio of 1.

That is, at the upper limit of conditional expression 3, the ratio of the amount of movement between the second lens group GR2 and the third lens group GR3 is 1:
When the value approaches 1, the load on the third lens group GR3 becomes heavy and the balance of the lens system becomes poor. These second lens group GR2 and third lens group G
As for R3, roughly speaking, it is desirable that the second lens group GR2 corrects the image plane and that the third lens group GR3 perform spherical aberration.

In order to correct spherical aberration and coma,
It is desirable that the lens having the positive refractive power of the third lens group GR3 be configured to include an aspherical surface.

When both surfaces of the biconvex lens are aspherical surfaces, if the radius of curvature of the reference spherical surface on the object side is r _{o bj} and the radius of curvature of the reference spherical surface on the image side is r _Img , then 2 <| r _img / r _obj | <3 holds.

Both surfaces of the biconvex lens are aspherical.
When Amount of sag on the object side surface: ΔZ_obj= | A ・ H^Four
＋ B ・ H⁶+ C ・ H⁸+ D ・ H¹⁰｜, Amount of sag on the image side: ΔZ_img= | A ・ H^Four＋ B ・ H
⁶+ C ・ H⁸+ D ・ H^{1 0}｜ Using, the aspheric amount is the one that simultaneously satisfies
is there. When H = He, 0.26 <| ΔZ_img/ ΔZ_obj| <0.5, When H = 0.75 He, 0.36 <| ΔZ_img/ ΔZ_obj| <0.9 In the above equation, | ΔZ_img/ ΔZ_objThe value of | is lower
Beyond the limit, the change in meridional image plane during zooming
It becomes large, and the outer coma aberration increases. Also, |
ΔZ_img/ ΔZ_objIf the value of | exceeds the upper limit, wide-angle
Intermediate focal length (angle of view)
Inward coma tends to remain in the entire zoom range.
For reference, in the numerical examples described later, the third lens
The aspherical surface is included in the lens having positive refractive power of the lens group GR3.
Numerical Examples 1 to 3 | ΔZ _img/ ΔZ_obj｜
Are shown in Table 1 below.

[0030]

[Table 1]

The zoom lens of the present _invention, and the refractive index at e-line of the lens having the positive refractive power of the fourth lens group _{NPL GR4,} configured to satisfy the _NPL GR4> 1.7 (Condition 4) It is desirable to do.

That is, in the conditional expression 4, when the value of nPL _GR4 falls below 1.7, the Petzval sum increases and the image plane becomes under. By introducing an aspherical surface, it is possible to correct the meridional image surface to the over side, but with a glass material with a low refractive index, the astigmatic difference (the difference between the sagittal image surface and the meridional image surface) is large. I will remain.

Next, numerical examples 1 to 4 embodying the zoom lens of the present invention will be described.

In the following description, "ri" is the i-th lens surface counted from the object side and its radius of curvature, "di".
Is the i-th lens surface ri and the i + 1-th lens surface r
“Ni” is the refractive index of the material forming the i-th lens Li at the d-line, and “νi” is the Abbe number of the material forming the i-th lens. Similarly, "n
“FL” and “νFL” are the refractive index and Abbe number at the e-line of the material forming the filter FL, respectively.

Further, the definition of the aspherical surface is as follows: Z = Z, where "Z" is the sag amount (depth of the aspherical surface) from the tangent plane at the apex of the surface, and "H" is the vertical height from the optical axis. ^{H 2 / ri {1+ (1} -H 2 / ri 2) 1/2} +
And those represented by ^{A · H 4 + B · H} 6 + C · H 8 + D · H 10.

The zoom lens 1 according to Numerical Example 1 includes
As shown in the lens arrangements at the wide-angle end and the telephoto end in FIGS. 1 and 2, in order from the object side, the first lens group GR1 has a positive refractive power and is always fixed in position, and a negative refractive power. And a second lens group GR2 having a movable position and a third lens group GR3 having a positive refractive power and a movable position.
And a fourth lens group GR4 having a positive refracting power and movable in position, the first lens group GR1.
Is a biconvex first lens L1, and the second lens group GR2 is a second lens L2 which is a concave meniscus lens having a convex surface facing the object side and a third lens which is a convex meniscus lens having a convex surface facing the object side. And L3. The third lens group GR3 includes a fourth lens L4, which is a biconvex lens having a positive refractive power, and a fifth lens L, which is a concave meniscus lens having a negative refractive power and having a convex surface directed toward the object side.
5, and the fourth lens group GR4 is composed of a sixth lens L6 which is a biconvex lens.

An aspherical fifth surface r5 is formed of a resin layer on the image-side surface r4 of the second lens (concave meniscus lens) L2 of the second lens group GR2.

Further, an aperture stop IR is arranged between the second lens group GR2 and the third lens group GR3, and the fourth lens group GR4
Between the lens group GR4 and the image plane IMG, a filter FL including a low-pass filter, a cover glass of the image sensor, etc.
Is provided.

Table 2 below shows numerical values of the zoom lens 1. In addition, a symbol (ASP) is added to the surface formed by the aspherical surface (the same applies to the same type of table in each numerical example below).

[0040]

[Table 2]

In Table 3, the focal length f of the zoom lens 1 and the F number FNo. , A half angle of view ω, and numerical values at the telephoto end and the wide-angle end of the surface distances d2, d7, d8, d12, and d14 that change according to zooming and focusing.

[0042]

[Table 3]

Table 4 shows the fifth surface r formed by an aspherical surface.
5 shows fourth-order to tenth-order aspherical surface coefficients A to D of the ninth surface r9, the tenth surface r10, and the fourteenth surface r14.

[0044]

[Table 4]

3 and 4 show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the zoom lens 1, respectively. In the spherical aberration diagram, the solid line is the e-line (wavelength 54
6.07 nm), the broken line shows the value at the g line (435.84 nm), and the alternate long and short dash line shows the value at the C line (656.27 nm).
The solid line shows the values on the sagittal image plane, and the broken line shows the values on the meridional image plane (FIG. 7, FIG. 8, FIG. 11, which will be described later).
The same applies to FIGS. 12, 15 and 16. As shown in FIGS. 3 and 4, it is understood that the zoom lens 1 has various aberrations corrected well.

The zoom lens 2 in Numerical Example 2 includes
As shown in the lens arrangements at the wide-angle end and the telephoto end in FIGS. 5 and 6, in order from the object side, the first lens group GR1 has a positive refractive power and is always fixed in position, and a negative refractive power. And a second lens group GR2 having a movable position and a third lens group GR3 having a positive refractive power and a movable position.
And a fourth lens group GR4 having a positive refracting power and movable in position, the first lens group GR1.
Is a biconvex first lens L1, and the second lens group GR2 is a second lens L2 which is a concave meniscus lens having a convex surface facing the object side and a third lens which is a convex meniscus lens having a convex surface facing the object side. And L3. The third lens group GR3 includes a fourth lens L4, which is a biconvex lens having a positive refractive power, and a fifth lens L, which is a concave meniscus lens having a negative refractive power and having a convex surface directed toward the object side.
5, and the fourth lens group GR4 is composed of a sixth lens L6 which is a biconvex lens.

A diaphragm IR is provided between the second lens group GR2 and the third lens group GR3, and a low-pass filter and an image pickup device are provided between the fourth lens group GR4 and the image plane IMG. Filter F composed of element cover glass, etc.
L is provided.

Table 5 below shows each numerical value of the zoom lens 2.

[0049]

[Table 5]

Table 6 shows the focal length f of the zoom lens 2 and the F number FNo. , A half angle of view ω, and numerical values at the telephoto end and the wide-angle end of the surface distances d2, d6, d7, d11, and d13 whose distances change due to zooming and focusing.

[0051]

[Table 6]

Table 7 shows the eighth surface r formed by an aspherical surface.
8 shows the fourth-order to tenth-order aspherical surface coefficients A to D of the ninth surface r9 and the thirteenth surface r14.

[0053]

[Table 7]

7 and 8 show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the zoom lens 2, respectively. As shown in FIGS. 7 and 8, the zoom lens 2
Shows that various aberrations are well corrected.

The zoom lens 3 according to Numerical Example 3 includes
As shown in the lens arrangements at the wide-angle end and the telephoto end in FIGS. 9 and 10, in order from the object side, the first lens group GR1 has a positive refractive power and is always fixed in position, and a negative refractive power. And a second lens group GR2 having a movable position, and a third lens group GR having a positive refractive power and a movable position.
3 and a fourth lens group GR4 having a positive refracting power and capable of moving its position, and includes a first lens group GR1.
Is a biconvex first lens L1, and the second lens group GR2 is a second lens L2 which is a concave meniscus lens having a convex surface facing the object side and a third lens which is a convex meniscus lens having a convex surface facing the object side. And L3. The third lens group GR3 includes a fourth lens L4, which is a biconvex lens having a positive refractive power, and a fifth lens L, which is a concave meniscus lens having a negative refractive power and having a convex surface directed toward the object side.
5, and the fourth lens group GR4 is composed of a sixth lens L6 which is a biconvex lens.

A diaphragm IR is provided between the second lens group GR2 and the third lens group GR3, and a low-pass filter and an image pickup device are provided between the fourth lens group GR4 and the image plane IMG. Filter F composed of element cover glass, etc.
L is provided.

Table 8 below shows numerical values of the zoom lens 3.

[0058]

[Table 8]

Table 9 shows the focal length f of the zoom lens 3 and the F number FNo. , A half angle of view ω, and numerical values at the telephoto end and the wide-angle end of the surface distances d2, d6, d7, d11, and d13 whose distances change due to zooming and focusing.

[0060]

[Table 9]

Table 10 shows the fourth-order to tenth-order aspherical surface coefficients A to D of the eighth surface r8 and the ninth surface r9 which are aspherical surfaces.

[0062]

[Table 10]

11 and 12 show spherical aberration, astigmatism and distortion at the wide-angle end and the telephoto end of the zoom lens 2. As shown in FIGS. 11 and 12, it can be seen that the zoom lens 3 has various aberrations favorably corrected.

The zoom lens 4 according to Numerical Example 4 is
As shown in the lens arrangements at the wide-angle end and the telephoto end in FIGS. 13 and 14, the first lens group GR1 having a positive refracting power and always fixed in position from the object side, and the negative refracting power in order from the object side. And a second lens group GR2 having a movable position, and a third lens group G having a positive refractive power and a movable position.
R3 and the fourth, which has a positive refractive power and is movable in position
And a first lens group GR.
1 is constituted by the first lens L1 which is a biconvex lens,
The second lens group GR2 is composed of a second lens L2 which is a concave meniscus lens having a convex surface facing the object side and a third lens L3 which is a convex meniscus lens having a convex surface facing the object side. The third lens group GR3 includes a fourth lens L4, which is a convex meniscus lens having a positive refractive power and having a gentle concave surface on the object side and a convex surface on the image side, and a convex lens having a strong convex surface on the object side. 5 lens L5 and a cemented lens with a sixth lens L6 which is a concave lens having a negative refracting power and having a concave surface facing the image side, and the fourth lens group GR4 is constituted by a seventh lens L7 which is a biconvex lens. To be done.

An aspherical fifth surface r5 is formed of a resin layer on the image-side surface r4 of the second lens (concave meniscus lens) L2 of the second lens group GR2.

A stop IR is provided between the second lens group GR2 and the third lens group GR3, and the fourth
Between the lens group GR4 and the image plane IMG, a filter FL including a low-pass filter, a cover glass of the image sensor, etc.
Is provided.

Table 11 below shows numerical values of the zoom lens 4.

[0068]

[Table 11]

Table 12 shows focal lengths f and F of the zoom lens 4.
Number FNo. , Half angle of view ω, surface spacings d2, d7, d8, d13, d15 that vary with zooming and focusing
The numerical values at the telephoto end and the wide-angle end of are shown.

[0070]

[Table 12]

Table 13 shows the fourth-order to tenth-order aspherical surface coefficients A to D of the fourth surface r4 and the eleventh surface r11 which are aspherical surfaces.

[0072]

[Table 13]

15 and 16 show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the zoom lens 4, respectively. As shown in FIGS. 15 and 16, it can be seen that the zoom lens 4 has various aberrations favorably corrected.

Finally, Table 14 below shows each value relating to the conditional expressions 1 to 4 of the zoom lenses 1 to 4 in the numerical examples 1 to 4.

[0075]

[Table 14]

As shown in Table 14 above, the zoom lens 1
To 3 are conditional expressions 1 to 4, and the zoom lens 4 is conditional expression 1
To 3 are satisfied.

As described above, in the zoom lenses 1 to 4, the second lens group GR2 and the third lens group GR3 move at a constant ratio to change the magnification, and the first lens group GR1 becomes Since the structure does not move, the total length does not change, so that it is easy to handle even when applied to various imaging devices. In addition, since the position of the diaphragm IR is also fixed, it is possible to freely arrange the diaphragm adjusting mechanism, which is advantageous for downsizing of the whole.

Further, since the zoom lenses 1 to 4 use a convex lens for the front lens (first lens L1), it is possible to efficiently correct distortion.

Further, in the zoom lenses 1 to 4, since the second lens group GR2 and the third lens group GR3 used for zooming move at a constant ratio, these drives are
For example, it can be easily performed by a simple structure such as a cam barrel, and the second lens group and the third lens group can be used without using a cam barrel having a complicated cam curve.
The second so that the lens group moves in the opposite direction on the optical axis.
For the lens group and the third lens group, use a lead screw threaded in the opposite direction at a ratio of pitch 2: 1,
It is also possible to move the second lens group and the third lens group at the same time with one actuator by converting the second lens group and the third lens group into different rotational speeds by the reduction gears.

Furthermore, the zoom lenses 1 to 4 are sufficiently bright with an open F value of 2.83 to 2.85, and
Since the distance of the exit pupil is sufficiently long, it is suitable for an apparatus using an image sensor.

The specific shapes and structures of the respective portions shown in the above-mentioned embodiments are merely examples of the implementation of the present invention. The scope should not be limitedly interpreted.

[0082]

As described above, according to the zoom lens of the present invention, in order from the object side, the first lens group having a positive refractive power and the position thereof is always fixed, and the position having a negative refractive power are arranged. Is movable, a third lens group having a positive refractive power and a movable position, and a fourth lens group having a positive refractive power and a movable position. In the zoom lens configured by, the first lens group includes a biconvex lens, and the second lens group includes a concave meniscus lens having a convex surface directed toward the object side and a convex meniscus lens having a convex surface directed toward the object side. , The third lens group includes at least one aspherical lens having a positive refractive power and one lens having a negative refractive power, and the fourth lens group includes a biconvex lens, Lens group and third
The lens group is moved at a constant ratio with an aperture stop whose position is fixed with respect to the image pickup surface to perform zooming, and the fourth lens group is moved to change the image point. Since the correction is made, the total length does not change, so it is easy to handle even when applied to various imaging devices. In addition, since the position of the aperture IR is fixed, the aperture adjustment mechanism can be freely arranged, and It is advantageous for downsizing.

In the invention described in claim 2, the second aspect
The lens having a negative refractive power of the lens group includes an aspherical surface, and νPL _{GR2 is set} to the Abbe number at the e-line of the lens having a positive refractive power of the second lens group, nNL.
_GR2 is the value of e of the lens having negative refractive power of the second lens group.
If the refractive index at the line is nNL _GR2 > 1.8, ν
Since each condition of PL _GR2 <28 is satisfied,
The axial chromatic aberration is not overcorrected at the telephoto end, and various aberrations such as distortion can be favorably corrected.

According to the invention described in claim 3,
Lens group and the third lens group 2: while moving in a ratio, the focal length of the f ₂ second lens group and a focal length at the wide angle end of the f _w the whole lens system, 2 <| f ₂ / f _w
Since the condition of | <2.8 is satisfied, the curvature of field can be effectively corrected, and at the same time, the second
The lens group and the third lens group can be easily driven by a simple structure such as a cam barrel, and
For example, the second lens group and the third lens group are moved such that the second lens group and the third lens group move in opposite directions on the optical axis without using a cam barrel having a complicated cam curve. With, a lead screw threaded in the opposite direction at a pitch of 2: 1 can be used,
It is also possible to move the second lens group and the third lens group at the same time with one actuator, for example, by converting the rotational speeds of the lens group and the third lens group to different ones.

In the invention described in claim 4, nP
_Letting L _{GR4 be} the refractive index at the e-line of the lens having a positive refractive power in the fourth lens group, the condition of nPL _GR4 > 1.7 is satisfied, so that the astigmatic difference due to the introduction of the aspherical surface is effective. Can be corrected dynamically.

[Brief description of drawings]

FIG. 1 shows Numerical example 1 in the embodiment of the zoom lens of the present invention, together with FIGS. 2 to 4, and is a diagram schematically showing the lens arrangement at the wide-angle end.

FIG. 2 is a diagram schematically showing a lens arrangement at a telephoto end.

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

FIG. 4 is a diagram showing spherical aberration, distortion, and astigmatism at the telephoto end.

FIG. 5 shows Numerical example 2 in the embodiment of the zoom lens of the present invention together with FIGS. 6 to 8, and is a diagram schematically showing the lens arrangement at the wide-angle end.

FIG. 6 is a diagram schematically showing a lens arrangement at a telephoto end.

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

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

FIG. 9 shows Numerical example 3 in the embodiment of the zoom lens according to the present invention, together with FIGS.
This figure is a diagram schematically showing the lens arrangement at the wide-angle end.

FIG. 10 is a diagram schematically showing a lens arrangement at a telephoto end.

FIG. 11 is a diagram showing spherical aberration, distortion, and astigmatism at the wide-angle end.

FIG. 12 is a diagram showing spherical aberration, distortion, and astigmatism at the telephoto end.

FIG. 13 shows Numerical example 4 in the embodiment of the zoom lens of the present invention, together with FIGS. 14 to 16, and is a diagram schematically showing the lens arrangement at the wide-angle end.

FIG. 14 is a diagram schematically showing a lens arrangement at a telephoto end.

FIG. 15 is a diagram showing spherical aberration, distortion, and astigmatism at the wide-angle end.

FIG. 16 is a diagram showing spherical aberration, distortion, and astigmatism at the telephoto end.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Zoom lens, 2 ... Zoom lens, 3 ... Zoom lens, 4 ... Zoom lens, GR1 ... 1st lens group, GR2
... 2nd lens group, GR3 ... 3rd lens group, GR4 ... 4th
Lens group, IR ... Aperture

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA02 KA03 MA15 PA06 PA17                       PA18 PB06 PB07 QA02 QA07                       QA14 QA22 QA25 QA34 QA42                       QA45 RA05 RA12 RA13 RA32                       RA43 SA23 SA27 SA29 SA32                       SA63 SA64 SA72 SB02 SB13                       SB23 SB24 SB32

Claims (4)

[Claims] 1. A first lens group having a positive refracting power and a fixed position, and a second lens group having a negative refracting power and a movable position in this order from the object side. A zoom lens including a third lens group having a positive refractive power and a movable position, and a fourth lens group having a positive refractive power and a movable position, wherein The lens group is configured by a biconvex lens, the second lens group is configured by a concave meniscus lens having a convex surface facing the object side and a convex meniscus lens having a convex surface facing the object side, and the third lens group is at least It is composed of one aspherical lens having a positive refractive power and one lens having a negative refractive power, the fourth lens group is composed of a biconvex lens, and the second lens group and the third lens group. The position is fixed with respect to the image plane. The zoom lens is adapted to perform zooming by moving the diaphragm with a fixed ratio, and the fourth lens group is also adapted to correct the fluctuation of the image point. Zoom lens to do. 2. The lens having a negative refractive power of the second lens group includes an aspherical surface, and satisfies the following conditions. Zoom lens. νPL _GR2 <28 nNL _GR2 > 1.8 where νPL _GR2 : Abbe's number at the e-line of the lens having the positive refractive power of the second lens group, nNL _GR2 : of the lens having the negative refractive power of the second lens group The refractive index at the e-line. 3. The second lens group and the third lens group are moved at a ratio of 2: 1 and the following condition is satisfied: Zoom lens. 2 <| f ₂ / f _w | <2.8, where f _{2 is} the focal length of the second lens group, and f _w is the focal length at the wide-angle end of the entire lens system. 4. The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditions. nPL _GR4 > 1.7 where nPL _GR4 is the refractive index at the e-line of the lens having the positive refractive power of the fourth lens group.