JPH0961703A - Focus position correcting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the positional deviation of the best image surface caused by the change of a diaphragm diameter all over a focal distance range by driving a focusing group by an adjusting amount obtained according to focus information and diaphragm information. SOLUTION: This device is provided with an, adjusting amount arithmetic means for calculating the adjusting amount of at least one lens group of a zoom lens by an operation expression based on focal distance information for regulating variation corresponding to the focal distance of a lens entire system, the diaphragm information for regulating the variation corresponding to the diaphragm diameter of the aperture diaphragm and a specified correction factor previously stored. According to the focal distance information and the diaphragm information, the adjusting amount of the focusing lens group G3 is decided based on the specified correction factor previously stored in a camera main body and the operation expression. By driving the focusing lens group G3 by the adjusting amount obtained in such a way, the best image surface and the film surface are controlled to be aligned over each focal distance state and each diaphragm state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus position correction device, and more particularly to a focus position correction device for correcting a shift of the best image plane due to a narrowing of a photographing lens in a camera equipped with a zoom lens.

[0002]

2. Description of the Related Art Generally, a lens has residual aberration even after aberration correction. Since spherical aberration and axial chromatic aberration remain in the taking lens, the best image plane and the Gaussian image plane are displaced from each other in the optical axis direction. Then, the lens barrel is designed so that the best image plane with the highest performance coincides with the film plane.

In a taking lens used for a camera or the like, it is used not only when the diaphragm is open, but also when the diaphragm is narrowed down. Then, usually, the best image plane in the open state of the diaphragm is designed to coincide with the film plane. Therefore, narrowing down improves the performance of the entire screen, but since spherical aberration remains in the shooting lens as described above, the best image plane position shifts in the optical axis direction and shifts from the film plane when narrowed down. I will end up.

If the spherical aberration of the taking lens is not sufficiently corrected, the amount of deviation between the best image plane position and the film plane position becomes large. Therefore, when the aperture is narrowed down, a focus shift (focus shift) occurs. For this reason, in the taking lens, it is necessary to suppress the occurrence of spherical aberration and suppress the movement of the best image plane position when the aperture is narrowed down.

By the way, in recent years, cameras equipped with zoom lenses have become common. In a zoom lens, the use magnification of all or some of the lens groups that make up the zoom lens changes as the magnification changes, and the height of light rays that pass through each lens group changes as the magnification changes. Change,
Each lens group has residual aberration. Therefore, in the zoom lens, the correction state of the spherical aberration and the axial chromatic aberration changes due to the change of magnification due to the change of the use magnification, the change of the height of the light beam, and the residual aberration.

In the zoom lens, the lens barrel is designed so that the best image plane position, not the Gaussian image plane position, is constant over the entire focal length range from the wide-angle end to the telephoto end. However, as described above, the correction state of spherical aberration and axial chromatic aberration varies with zooming, so the amount of movement of the best image plane position when the aperture is narrowed changes with zooming.

[0007]

Generally, suppressing the movement of the best image plane position when the aperture is narrowed down causes an excessive constraint in correcting aberrations. In particular, in the case of a zoom lens, in order to suppress the movement of the best image plane position when focusing is performed over the entire focal length range, it is necessary to suppress the variation of spherical aberration and axial chromatic aberration to an extremely small value. As a result, there was no choice but to cause an increase in the number of lens components and an increase in size of the lens system.

The present invention has been made in view of the above-mentioned problems, and corrects the positional deviation of the best image plane due to the change of the aperture diameter over the entire focal length range of the zoom lens mounted on the camera. It is an object of the present invention to provide a focus position correction device that can be used.

[0009]

In order to solve the above-mentioned problems, according to the present invention, in a focus position correcting device for a camera equipped with a zoom lens, a focus which defines a variation amount corresponding to the focal length of the entire lens system. The adjustment amount δh of at least one lens group Gh of the zoom lens is calculated by an arithmetic expression based on the distance information and the aperture information that defines the amount of change corresponding to the aperture diameter of the aperture diaphragm and a predetermined correction coefficient stored in advance. And an adjustment amount calculating means for adjusting the lens position Gh in each focal length state so as to correct the focal position shift of the best image surface with respect to the film surface due to the change of the diaphragm diameter over the entire zooming region. A focus position correcting device is provided, which is provided with a drive unit for moving the adjustment amount δh along the optical axis.

According to a preferred aspect of the present invention, the lens group Gh has a variable use magnification during zooming and is movable during focusing. Further, the adjustment amount calculating means calculates the following calculation formula based on the correction coefficient a _ij , the focal length information f, and the aperture information φ: δh = Σa _ij f ⁱ φ ^j (i = 0,1,2) It is preferable to calculate the adjustment amount δh according to ..., j = 0,1,2 ...).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In a zoom lens, in order to simplify the lens barrel structure, it is mainstream to move some lens groups of the lens system along the optical axis at the time of focusing. In recent years, cameras having an autofocus function have become the mainstream. Particularly, as the speed of focusing increases, the front focus (F) that drives the first lens unit arranged closest to the object side to perform focusing
In comparison with the F) method, an inner focus (IF) method and a rear focus (RF) method, which drive a lens group arranged on the image side of the first lens group to perform focusing, are becoming mainstream.

The IF system and the RF system are becoming mainstream rather than the FF system because the FF system drives the first lens group having a large lens diameter, while the IF system and the RF system are driven.
This is because the method drives a lens group having a smaller lens diameter. That is, the IF method and the RF method can perform focusing with a smaller work amount (= weight × driving amount) than the FF method, and are suitable for higher speed.

In the non-TTL-AF type camera, the position of the subject is detected by a distance measuring optical system provided separately from the taking lens. Then, depending on the position of the detected subject,
Focusing is performed by driving the focusing lens group. At this time, the required drive amount of the focusing lens group corresponding to each subject position is calculated by a predetermined arithmetic expression based on a predetermined storage coefficient and subject position information stored in advance in the camera body. Then, the focusing lens group is driven by the calculated required driving amount, that is, the focusing driving amount to focus on the subject.

Particularly, in the IF type or RF type zoom lens, the focusing drive amount of the focusing lens group with respect to the same subject position changes with zooming. Therefore, the focusing drive amount is calculated based on both the focal length information and the subject position information. Then, the focusing lens group is driven by the calculated focusing drive amount to focus on the subject.

By the way, as described above, since spherical aberration and axial chromatic aberration remain in the taking lens even after the aberration correction, the best image plane and the Gaussian image plane are deviated in the optical axis direction. Here, the best image plane position is the position where the optical performance is highest when the diaphragm is open, and usually indicates the position where the optical performance is best in the center of the screen. Further, as described above, in the zoom lens, the correction state of spherical aberration and axial chromatic aberration changes with zooming. Therefore, the amount of deviation between the best image plane and the Gaussian image plane changes with zooming, and the amount of movement of the best image plane due to narrowing down also changes with zooming.

In this specification, the defocus amount is defined as the shift amount along the optical axis of the best image plane position in the narrowed down state, with reference to the best image plane position in the fully opened state. Then, when the best image plane position when narrowed down is shifted in the traveling direction of the light beam, the sign of the defocus amount is set to be positive.

FIG. 1 shows spherical aberration correction states (a) to (a).
It is a figure showing (d). In FIG. 1, the correction state (a)
Shows a state in which the negative spherical aberration increases as it becomes brighter, and the corrected state (b) shows a state in which the negative spherical aberration once increases and then the positive spherical aberration increases as it becomes brighter. In the correction state (c), the positive spherical aberration increases as the brightness increases, and in the correction state (d), the positive spherical aberration increases and then the negative spherical aberration increases as the brightness increases. Are shown respectively.

In the correction state (a), the defocus amount changes to the positive side as the diaphragm is narrowed down. In the case of the correction state (b), the day focus amount further changes to the negative side and then to the positive side as the diaphragm is narrowed. In the correction state (c), the defocus amount changes to the negative side as the diaphragm is narrowed. In the case of the correction state (d), the day focus amount further changes to the positive side and then to the negative side as the diaphragm is narrowed.

Next, when the axial chromatic aberration is insufficiently corrected or the axial chromatic aberration is excessively corrected, the positions of the best image plane and the Gaussian image plane do not match, but the amount of deviation depends on the aperture diameter. It becomes almost constant without any. Also, when the correction state of spherical aberration changes depending on the wavelength of light, it is also affected by the correction state of spherical aberration at the reference wavelength. Therefore, as a result, it is considered that the change in the defocus amount when the aperture diameter changes is determined based on the correction state of the spherical aberration at the reference wavelength.

In general, when the focusing lens group, which is a part or the whole of the lens system, is moved in the optical axis direction with respect to a subject at a predetermined position, the image plane position is moved in the optical axis direction. The ratio of the amount of movement of the image plane position to the amount of drive of the focusing lens group at this time is called the image plane movement coefficient. The image plane movement coefficient depends on the use magnification of the lens unit arranged on the image side of the focusing lens unit. Therefore, in the case of a zoom lens, the image plane movement coefficient changes with zooming.

By the way, the focusing lens group is designed so that good imaging performance can be obtained even if it is driven over each photographing distance from a long-distance object to a short-distance object. Therefore, even if the focusing lens group is driven in the optical axis direction, the aberration variation due to the driving is small. Further, the focusing lens group can be continuously driven in the optical axis direction by the driving mechanism. Therefore, by driving the focusing lens group by a predetermined amount, it is possible to correct the variation of the best image plane position due to the change of the aperture diameter, and match the best image plane and the film plane.

In the zoom lens, as described above, the image plane movement coefficient changes as the magnification changes. Therefore, even if the change in the defocus amount due to the change in the aperture diameter is constant over each focal length state without depending on the magnification change, the focusing lens group is driven to correct the constant defocus amount. The amount, that is, the adjustment amount, changes as the magnification changes. Therefore, in the present invention, by driving the focusing lens group by an adjustment amount according to the focal length information and the aperture information, the best image plane and the film surface match each focal length state and each aperture state. To control.

In particular, in the present invention, the adjustment amount of the focusing lens group is determined based on the predetermined correction coefficient and the arithmetic expression stored in advance in the camera body in accordance with the focal length information and the aperture information. In this way, by driving the focusing group by the calculated adjustment amount, it is possible to control so that the best image plane and the film plane match in each focal length state and each aperture state.

Specifically, in the present invention, the adjustment amount δh for correcting the defocus amount due to the change of the aperture diameter.
By using the following polynomial (1) as an arithmetic expression for obtaining, the defocus amount can be easily corrected with a small storage capacity. δh = Σa _ij f ⁱ φ ^j (i = 0,1,2 ..., j = 0,1,2 ...) (1)

Here, δh: Adjustment amount of focusing lens group a _ij : Correction coefficient f: Focal length information φ: Aperture information As described above, the correction coefficient a _ij is stored in advance in the camera body. is there.

As the focal length information, for example, in addition to the drive amount for zooming one lens group, information about the rotation angle of the lens barrel during zooming can be used. That is, as long as the amount changes during zooming and the focal length can be uniquely calculated based on the change, it can be used as the focal length information.

As described above, the focusing lens group can be continuously moved along the optical axis and can be easily driven by electric control. Therefore, in the above description, discussion has been limited to the method of correcting the defocus amount by driving the focusing lens group by the adjustment amount. However, it is obvious that the adjusting method of the present invention can be applied to any lens group that can be continuously moved and can be driven by electrical control.

Generally, even if the focal length is the same, if the position of the subject changes, the correction state of spherical aberration will change. Therefore, when the change in the spherical aberration correction state due to the change in the subject position (that is, the shooting distance) is large, the following polynomial (2) can be used instead of the above polynomial (1). That is, according to the polynomial (2), the adjustment amount δh according to changes in the subject position information (shooting distance information), the focal length information, and the aperture information is obtained, and the defocus amount according to the change in the aperture diameter is adjusted appropriately. It is possible.

Δh = Σa _ijk f ⁱ φ ^j R ^-k (i = 0,1,2 ..., j = 0,1,2 ..., k = 0,1,2 ...) (2 Here, a _ijk : correction coefficient f: focal length information φ: aperture information R: shooting distance information Note that the correction coefficient a _ijk is stored in advance in the camera body.

According to another aspect, the taking lens is required to have a certain number of resolutions or more, but a depth of focus for satisfying the requirement of the number of resolutions is conceivable. For example, the resolution of the human eye is said to be θ = 1 '(minutes),
When expanding to service size, enlargement ratio β
Is about 3 times. This photo is a clear distance L (250m
Considering observation with m), the resolution K on the film surface is expressed by the following equation (a).

[0031]

## EQU00001 ## K = .theta..multidot.L = {2.pi.L / (360.60)} /. Beta. = 0.02424 [mm] (a) Therefore, the number of resolutions k necessary for observation is calculated by the following equation (b). ) Is given. k = 1 / K = 41.25 [lines / mm] (b)

When the aperture ratio at this time is FNO,
The depth of focus S in the optical axis direction is expressed by the following equation (c). S = ± K · FNO = ± 0.02424 · FNO (c) Therefore, even if the focal position deviates from the film surface position within this depth of focus S, defocus (focal defocus) occurs.
Not observed as.

The depth of focus based on the above discussion does not allow the focus shift, but relates to the accuracy of the focal position of the camera. The required depth of focus also changes depending on the size of the film surface and the enlargement magnification. Further, since the focus shift is mostly due to the subjective judgment of the observer, the distance of clear vision and the number of resolutions also subjectively change. Therefore, the above specific numerical values are merely non-limiting numerical examples.

[0034]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each embodiment of the present invention, the aspherical surface is
The height in the direction perpendicular to the optical axis is y, the displacement amount in the optical axis direction at the height y is S (y), the reference radius of curvature, that is, the apex radius of curvature of the aspherical surface is r, the conic coefficient is κ, and When the aspherical surface coefficient is Cn, it is expressed by the following mathematical expression (d).

[Formula 2] S (y) = (r / κ) / [1- (1-κ · y ² / r ² ) ^1/2 ] + C ₄ · y ⁴ + C ₆ · y ⁶ + C ₈ · y ⁸ + C ₁₀・ Y ¹⁰ + ... (d) The aspherical surface in the specification table of each example is marked with * on the right side of the surface number.

[First Embodiment] FIG. 2 is a refractive power arrangement diagram at a wide-angle end (W) and a telephoto end (T) of a zoom lens to which a focus position correcting device according to a first embodiment of the present invention is applied. is there. The zoom lens of FIG. 2 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a third lens group G3 having a positive refractive power. It is composed of a fourth lens group G4 and a fifth lens group G5 having a negative refractive power.

During zooming from the wide-angle end to the telephoto end, the air gap between the first lens group G1 and the second lens group G2 increases, and the air gap between the second lens group G2 and the third lens group G3. Decreases, and the third lens group G3 and the fourth lens group G4
The lens groups move toward the object side such that the air distance between the lens groups increases and the air distance between the fourth lens group G4 and the fifth lens group G5 decreases. It should be noted that during zooming, the second lens group G2
And the fourth lens group G4 move integrally, and the third lens group G3 moves relatively to the second lens group G2 and the fourth lens group G4. Further, during focusing on a short-distance object, only the third lens group G3 moves toward the image side along the optical axis.

FIG. 3 is a view showing the lens arrangement of the zoom lens shown in FIG. The zoom lens of FIG. 3 includes, in order from the object side, a first lens group G1 including a cemented positive lens L1 including a biconvex lens and a negative meniscus lens having a concave surface facing the object side.
And a second lens group G2 including a biconcave lens L21, a biconvex lens L22, and a negative meniscus lens L23 having a concave surface facing the object side, a third lens group G3 including a biconvex lens L3, and a concave surface facing the object side. Negative meniscus lens L
41, a fourth lens group G4 including a positive lens L42 including a biconvex lens and a negative meniscus lens having a concave surface facing the object side, and a positive meniscus lens L43 having a concave surface facing the object side, and a concave surface facing the object side. Positive meniscus lens L5
1, a negative meniscus lens L52 having a concave surface facing the object side,
And a fifth lens group G5 including a negative meniscus lens 53 having a concave surface facing the object side.

The aperture stop S is arranged between the third lens group G3 and the fourth lens group G4. FIG. 3 shows the positional relationship between the lens groups at the wide-angle end, and when the magnification is changed to the telephoto end, the lens units move on the optical axis along the zoom orbit shown by the arrow in FIG.

The following table (1) lists the values of specifications of the first embodiment of the present invention. In Table (1), f is the focal length, F
NO represents the F number, 2ω represents the angle of view, Bf represents the back focus, and Δ represents the amount of extension of the first lens group G1 based on the wide-angle end as focal length information. Further, the surface number indicates the order of the lens surface from the object side along the direction in which the light beam travels, and the refractive index and Abbe number indicate values for the d-line (λ = 587.6 nm).

[0040]

[Table 1] f = 38.79 to 153.22 FNO = 3.89 to 10.00 2ω = 58.7 to 15.6 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 73.3723 4.02 1.48749 70.41 2 -41.3728 1.38 1.86074 23.01 3 -63.5060 (d3 = variable) 4- 40.8258 1.13 1.79668 45.37 5 21.8873 0.88 6 18.8014 3.14 1.78472 25.80 7 -125.2349 1.00 8 -20.9542 1.13 1.79668 45.37 9 -221.6481 (d9 = variable) 10 437.8482 2.13 1.51680 64.10 11 -20.1039 (d11 = variable) 12 ∞ 2.26 (aperture diaphragm S) ) 13 * -44.4771 1.26 1.58518 30.24 14 -62.7167 0.38 15 28.0309 3.39 1.48749 70.41 16 -14.9351 1.26 1.86074 23.01 17 -24.7823 2.01 18 -24.3656 1.63 1.49108 57.57 19 -20.8520 (d19 = variable) 20 -62.9139 3.14 1.80458 25.50 21-22.4 0.25 22 -53.4113 1.26 1.79668 45.37 23 -214.2797 4.27 24 -15.0687 1.50 1.77279 49.45 25 -828.1507 (Bf) (aspherical data) κ C ₄ 13 surface 1.0000 -0.2141 × 10 ^-4 C ₆ C ₈ C ₁₀ -0.4131 × 10 ^-7 -0.1680 × 10 ^-8 0.1023 × 10 ^-10 (Variable distance during zooming) Δ Focal length d3 d9 d11 d19 Bf FNO (A) 0.00 0 38.794 2.135 4.406 3.129 16.801 9.059 3.89 (B) 8.789 50.738 7.237 3.686 3.849 13.134 16.462 4.68 (C) 17.579 64.003 11.049 2.965 4.570 10.496 24.124 5.50 (D) 26.363 78.314 14.272 2.245 5.290 8.586 31.635 6.30 (E) 34.889 91.993 17.179 2.047 5.488 6.731 39.110 7.03 (F) 43.412 106.381 19.984 1.849 5.686 5.172 46.377 7.71 (G) 51.944 121.461 21.698 1.651 5.883 3.905 54.446 8.51 (H) 60.467 137.092 23.463 1.454 6.081 2.813 62.267 9.25 (I) 67.989 153.220 24.996 1.256 6.279 1.877 70.131

The aberration diagrams shown in FIGS. 4 to 8 are spherical aberration diagrams in the focal length states (A) to (I) of Table (1), respectively. In each aberration diagram, FN is the F number, H is the height of the incident light, and D is the d line (λ = 587.6n).
m) and G indicates the g-line (λ = 435.8 nm).

On the other hand, the drawings shown in FIGS. 9 to 11 are MTF diagrams in the respective focal length states (A) to (I) of Table (1). Each MTF diagram shows the MTF in the defocus direction in the center of the screen for a spatial frequency of 30 lines / mm in white, the horizontal axis represents the defocus amount of the best image plane with respect to the Gaussian image plane, and the vertical axis represents the contrast. Are shown respectively. As described above, the sign of the defocus amount has a negative movement toward the object side and a positive movement toward the image side.

In the figure, m1 indicates the open state of the aperture stop S, m
2 is the -0.5EV state, m3 is the -1EV state, m4
Indicate the -1.5 EV state, respectively. Also, DF
1, DF2, DF3 and DF4 are open, -0.5EV, -1EV and -1.5E, respectively.
The defocus amount of the best image plane (image plane with the highest contrast) in the V state with respect to the Gaussian image plane is shown. With reference to FIGS. 9 to 11, it can be seen that in each of the focal length states (A) to (I), the position of the best image plane varies with the change of the aperture diameter.

The following table (2) corresponds to the image plane movement coefficient in each focal length state, the defocus amount in each focal length state and each aperture state, and the defocus amount in each focal length state and each aperture state. The strict adjustment amount δh0 obtained by dividing by the image plane movement coefficient is shown.

[0045]

[Table 2] Defocus amount Strict adjustment amount δh0 Δ -1 / 2EV -1EV -1.5EV Transfer coefficient -1 / 2EV -1EV -1.5EV 0.000 -0.025 +0.000 +0.020 1.23 -0.0203 0.0000 +0.0163 8.789 -0.025 +0.015 +0.045 1.77 -0.0141 +0.0085 +0.0254 17.579 -0.025 +0.030 +0.070 2.44 -0.0102 +0.0123 +0.0287 26.363 -0.010 +0.055 +0.095 3.21 -0.0031 +0.0171 +0.0296 34.889 -0.010 +0.055 +0.090 3.91 -0.0026 +0.0141 + 0.0230 43.412 0.000 +0.060 +0.085 4.59 0.0000 +0.0131 +0.0185 51.944 +0.015 +0.070 +0.085 5.50 +0.0027 +0.0127 +0.0155 60.467 +0.060 +0.085 +0.080 6.40 +0.0094 +0.0133 +0.0125 67.989 +0.095 +0.090 +0.060 7.36 + 0.0129 +0.0122 +0.0082

When the aperture diameter of the aperture stop S is set to φ0,
When the aperture diameter when the aperture is narrowed down is φ1, the aperture value F is given by the following equation (3). F = log ₂ (φ0 / φ1) (3) In the first embodiment, the first lens group G1 is based on the wide-angle end.
The amount of adjustment Δ of the third lens group G3, which is the focusing lens group, is calculated by the following equation (4) corresponding to the equation (1), using the amount of extension Δ of the focal length information as the focal length information and the aperture value F as the aperture information. There is. Thus, in the first embodiment, the adjustment amount δh is set to the strict adjustment amount δ based on the above polynomial (4).
It is possible to approximate h0 with high accuracy. ^{_{δh = Σa ij Δ i F j}} (i = 0,1,2,3 j = 1,2,3) (4) where the correction factor is as shown in the following table (3).

[0047]

[Table 3] a ₀₁ = -0.6066 × 10 ^-1 a ₀₂ = 0.4693 × 10 ^-1 a ₀₃ = -0.8298 × 10 ^-2 a ₁₁ = 0.1273 × 10 ^-2 a ₁₂ = -0.4534 × 10 ^-3 a ₁₃ = 0.5978 × 10 ^-4 a ₂₁ = -0.1595 × 10 ^-4 a ₂₂ = 0.3002 × 10 ^-6 a ₂₃ = 0.7207 × 10 ^-7 a ₃₁ = 0.2110 × 10 ^-6 a ₃₂ = -0.8067 × 10 ^-7 a ₃₃ = 0.1529 x 10 ^-7

As described above, in the first embodiment, the zooming range from the wide-angle end to the telephoto end is calculated based on the total 12 correction coefficients, the movement amount Δ due to the zooming of the first lens group, and the aperture value F. Adjustment amount of focusing lens group δh
Can be approximated well. Then, by driving the focusing lens group by the adjustment amount δh that is appropriately approximated, it is possible to satisfactorily correct the defocus amount due to the change in the aperture diameter over the entire variable power region.

[Second Embodiment] FIG. 12 is a refractive power arrangement diagram at a wide-angle end (W) and a telephoto end (T) of a zoom lens to which a focal position correcting apparatus according to a second embodiment of the present invention is applied. is there. The zoom lens of FIG. 12 includes, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a third lens group G3 having negative refractive power. 4th lens group G4 and 5th lens group G5 of negative refracting power
It is composed of

During zooming from the wide-angle end to the telephoto end, the air gap between the first lens group G1 and the second lens group G2 decreases, and the air gap between the second lens group G2 and the third lens group G3 decreases. Decreases, and the third lens group G3 and the fourth lens group G4
The lens groups move so that the air distance between the lens groups increases and the air distance between the fourth lens group G4 and the fifth lens group G5 decreases. That is, the second lens group G2 to the fifth lens group G5 move to the object side, and the first lens group G1 once moves to the image side and then moves to the object side. During zooming, the second lens group G2 and the fourth lens group G4 move integrally, and the third lens group G3 moves relatively to the second lens group G2 and the fourth lens group G4. To do. Further, during focusing on a short-distance object, only the third lens group G3 moves toward the object side along the optical axis.

FIG. 13 is a view showing the lens arrangement of the zoom lens shown in FIG. The zoom lens of FIG. 13 includes, in order from the object side, a first lens group G including a biconcave lens L11 and a positive meniscus lens L12 having a convex surface facing the object side.
The second lens group G2 includes a positive lens L2 including a biconvex lens and a negative meniscus lens having a concave surface facing the object side.
And a positive meniscus lens L31 having a convex surface facing the object side,
A third lens group G3 composed of a biconcave lens L32, a cemented positive lens L33 composed of a biconvex lens and a negative meniscus lens having a concave surface facing the object side, and a fourth lens group G4 composed of a biconcave lens L4.
It includes a lens group G4, a positive meniscus lens L51 having a concave surface facing the object side, and a fifth lens group G5 including a negative meniscus lens 52 having a concave surface facing the object side.

The aperture stop S is arranged between the third lens group G3 and the fourth lens group G4. FIG.
The positional relationship of each lens group at the wide-angle end is shown, and during zooming to the telephoto end, the lens units move on the optical axis along the zoom orbit shown by the arrow in FIG.

The following table (4) lists the values of specifications of the second embodiment of the present invention. In Table (4), f is the focal length, F
NO represents the F number, 2ω represents the angle of view, Bf represents the back focus, and θ represents focal length information indicating rotation angle information of the lens barrel (0 at the wide-angle end and 1 at the telephoto end). Further, the surface number indicates the order of the lens surface from the object side along the direction in which the light beam travels, and the refractive index and Abbe number indicate values for the d-line (λ = 587.6 nm).

[0054]

[Table 4] f = 28.8 to 80.8 FNO = 3.59 to 7.01 2ω = 76.7 to 30.8 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 -133.0401 1.41 1.83500 42.97 2 19.6778 3.84 3 23.4223 3.84 1.80518 25.46 4 53.7405 (d4 = variable) 5 23.9419 5.25 1.58913 61.24 6 -29.9494 1.02 1.84666 23.83 7 -45.7211 (d7 = variable) 8 15.7761 2.88 1.65160 58.44 9 715.7299 0.51 10 -46.8535 1.15 1.80610 33.27 11 17.4909 0.58 12 31.9319 3.84 1.59551 39.23 13 -16.6912 1.28 1.28 1.10 (d14 = variable) 15 ∞ 3.07 (aperture stop S) 16 -245.1548 1.02 1.83500 42.97 17 44.4955 (d17 = variable) 18 -76.8134 2.69 1.67270 32.17 19 -22.5339 2.82 20 -11.5314 1.28 1.77250 49.65 21 -24.1342 (Bf) (variable Focal length d4 d7 d14 d17 Bf FNO (A) 0.00 28.801 19.634 1.968 1.104 7.394 12.611 3.59 (B) 0.20 35.396 14.487 1.946 1.126 5.449 18.705 4.03 (C) 0.40 43.504 10.036 1.923 1.149 4.246 25.081 4.55 (D) 0.60 53.468 6.423 2.016 1.056 3.466 32.427 5.21 (E) 0.80 65 .715 3.572 2.224 0.848 2.844 41.394 6.03 (F) 1.00 80.767 1.277 2.433 0.639 2.127 52.544 7.01

The aberration diagrams of FIGS. 14 to 16 are spherical aberration diagrams in the focal length states (A) to (F) of Table (4), respectively. In each aberration diagram, FN is the F number, H is the height of the incident light, and D is the d line (λ = 587.6n).
m) and G indicates the g-line (λ = 435.8 nm).

FIGS. 17 and 18 show MT in each of the focal length states (A) to (F) in Table (4).
FIG. Each MTF diagram shows the MTF in the defocus direction in the center of the screen for a spatial frequency of 30 lines / mm in white, the horizontal axis represents the defocus amount of the best image plane with respect to the Gaussian image plane, and the vertical axis represents the contrast. Are shown respectively. As described above, the sign of the defocus amount has a negative movement toward the object side and a positive movement toward the image side.

In the figure, m1 indicates the open state of the aperture stop S, m
2 is the -0.5EV state, m3 is the -1EV state, m4
Indicate the -1.5 EV state, respectively. Also, DF
1, DF2, DF3 and DF4 are open, -0.5EV, -1EV and -1.5E, respectively.
The defocus amount of the best image plane (image plane with the highest contrast) in the V state with respect to the Gaussian image plane is shown. Referring to FIGS. 17 and 18, it can be seen that in each of the focal length states (A) to (F), the position of the best image plane fluctuates as the diaphragm diameter changes.

The following table (5) corresponds to the image plane movement coefficient in each focal length state, the defocus amount in each focal length state and each aperture state, and the defocus amount in each focal length state and each aperture state. The strict adjustment amount δh0 obtained by dividing by the image plane movement coefficient is shown.

[0059]

[Table 5] Defocus amount Strict adjustment amount δh0 θ -1 / 2EV -1EV -1.5EV Transfer coefficient -1 / 2EV -1EV -1.5EV 0.000 +0.030 +0.105 +0.160 2.09 +0.0144 +0.0502 +0.0766 0.200 +0.010 + 0.085 +0.145 2.60 +0.0038 +0.0327 +0.0558 0.400 -0.010 +0.065 +0.125 3.26 -0.0031 +0.0199 +0.0383 0.600 -0.020 +0.060 +0.125 4.17 -0.0048 +0.0144 +0.0300 0.800 -0.010 +0.080 +0.150 5.43 -0.0018 +0.0147 +0.0276 1.000 +0.005 +0.075 +0.100 7.23 +0.0007 +0.0104 +0.0138

Similar to the first embodiment, if the aperture diameter of the aperture stop S when opened is φ0 and the aperture diameter when the aperture is narrowed is φ1, the aperture value F is given by the following equation (3). F = log ₂ (φ0 / φ1) (3) In the second embodiment, 0 at the wide-angle end and 1 at the telephoto end.
Using the rotation angle information θ of the lens barrel as the focal length information and the aperture value F as the aperture information, the adjustment amount δh of the third lens group G3, which is the focusing lens group, is expressed by the following equation (1). We asked for it in 5). Thus, in the first embodiment, the adjustment amount δh can be approximated to the strict adjustment amount δh0 with high accuracy based on the above polynomial (5). δh = Σa _ij θ ⁱ F ^j (i = 0,1,4,7 j = 1,2,3) (5) However, each correction coefficient is as shown in the following table (6).

[0061]

[Table 6] a ₀₁ = -0.1417 × 10 ^-1 a ₀₂ = 0.5500 × 10 ^-1 a ₀₃ = -0.1083 × 10 ^-1 a ₁₁ = -0.1907 ^{_{a 12 = 0.9573 × 10 -1 a}} 13 = -0.1469 × 10 -1 a 41 = 0.9814 × 10 -1 a 42 = 0.2946 × 10 -1 a 43 = -0.8952 × 10 -2 a 71 = -0.3993 × 10 - ¹ a ₇₂ = -0.2392 x 10 ^-1 a ₇₃ = 0.2394 x 10 ^-2

As described above, in the second embodiment, based on the total of 12 correction coefficients, the lens barrel rotation angle information θ, and the aperture value F, the entire zoom area from the wide-angle end to the telephoto end is selected. Therefore, the adjustment amount δh of the focusing lens group can be satisfactorily approximated. Then, the adjustment amount δh that is closely approximated
By only driving the focusing lens group, it is possible to satisfactorily correct the defocus amount due to the change in the aperture diameter over the entire zoom region.

[0063]

As described above, according to the focus position correction device of the present invention, the best image plane position shift due to the change of the aperture diameter is caused over the entire focal length range of the zoom lens mounted on the camera. Can be corrected.

[Brief description of drawings]

FIG. 1 is a diagram showing correction states (a) to (d) of spherical aberration.

FIG. 2 is a refractive power arrangement diagram at a wide-angle end (W) and a telephoto end (T) of a zoom lens to which a focus position correcting device according to a first embodiment of the present invention is applied.

FIG. 3 is a diagram showing a lens configuration of the zoom lens of FIG.

4A and 4B are focal length states (A) and (B) of the first embodiment.
6 is a spherical aberration diagram in FIG.

5A to 5C are focal length states (C) and (D) of the first embodiment.
6 is a spherical aberration diagram in FIG.

FIG. 6 shows focal length states (E) and (F) of the first embodiment.
6 is a spherical aberration diagram in FIG.

FIG. 7 shows focal length states (G) and (H) of the first embodiment.
6 is a spherical aberration diagram in FIG.

FIG. 8 is a spherical aberration diagram in the focal length state (I) of the first example.

FIG. 9 is an MTF diagram in focal length states (A) to (C) of the first embodiment.

FIG. 10 shows focal length states (D) to (F) of the first embodiment.
3 is an MTF diagram in FIG.

FIG. 11 shows focal length states (G) to (I) of the first embodiment.
3 is an MTF diagram in FIG.

FIG. 12 is a refractive power arrangement diagram at a wide-angle end (W) and a telephoto end (T) of a zoom lens to which a focus position correction device according to a second example of the present invention is applied.

13 is a diagram showing a lens configuration of the zoom lens of FIG.

FIG. 14 is a spherical aberration diagram in focal length states (A) and (B) of the second example.

FIG. 15 is a spherical aberration diagram in focal length states (C) and (D) of the second example.

FIG. 16 is a spherical aberration diagram in focal length states (E) and (F) of the second example.

FIG. 17 shows focal length states (A) to (C) of the second embodiment.
3 is an MTF diagram in FIG.

FIG. 18 shows focal length states (D) to (F) of the second embodiment.
3 is an MTF diagram in FIG.

[Explanation of symbols]

 G1 first lens group G2 second lens group G3 third lens group G4 fourth lens group G5 fifth lens group S aperture stop

Claims (5)

[Claims] 1. A focal position correction device for a camera equipped with a zoom lens, comprising: focal length information defining a variation amount corresponding to a focal length of the entire lens system; and a diaphragm defining a variation amount corresponding to an aperture diameter of an aperture diaphragm. An adjustment amount calculation means for calculating the adjustment amount δh of at least one lens group Gh of the zoom lens by an arithmetic expression based on the information and a predetermined correction coefficient stored in advance, and the best value according to the change of the diaphragm diameter. Drive means for moving the lens group Gh along the optical axis by the adjustment amount δh in each focal length state so as to correct the focal position shift of the image plane with respect to the film surface over the entire zooming region. A focus position correction device comprising: 2. The focus position correcting apparatus according to claim 1, wherein the lens group Gh has a variable use magnification when zooming and is movable when focusing. 3. The adjustment amount calculating means is configured to correct the correction coefficient a.
_ij and the focal length information f and the following operation based on said aperture information phi formula ^{_{δh = Σa ij f i φ j}} (i = 0,1,2 ..., j = 0,1,2 .. .) Is used to calculate the adjustment amount δh. 4. The adjustment amount calculating means is configured to correct the correction coefficient a.
_ij and, with the focal length information f, and the aperture information phi, the following calculation formula .delta.h =? a _ijk based on the object distance information R which defines the distance to the object ^{f i φ j R -k (i} = 0, 1,2 ..., j = 0,1,
2. The focus position correcting device according to claim 1, wherein the adjustment amount δh is calculated by 2 ..., k = 0,1,2 ...). 5. The lens group Gh is a focusing lens group that is movable at the time of focusing, and the drive unit is based on photographing distance information that defines a distance to a subject and the focal length information, and the lens group Gh.
Further comprises a focusing movement amount calculation means for calculating the focusing movement amount δf of the lens group Gh, and the driving means is an amount represented by the sum of the focusing movement amount δf and the adjustment amount δh.
The focus position correction device according to claim 1, wherein the focus position correction device is configured to be moved along the optical axis.