JPH04293008A - Zoom lens system - Google Patents

Abstract

PURPOSE:To increase the focusing accuracy and to improve the operability by equalizing the quantity of rotary movement of a distance ring for the focusing of a focusing lens group to the angle of rotation of a rotary lens barrel which is prescribed by the track of movement for the focusing. CONSTITUTION:The zoom lens system consists of four lens groups, i.e., a 1st lens group G1 with positive refracting power, a 2nd lens group G2 with negative refracting power, a 3rd lens group G3 with positive refracting power, and a 4th lens group G4 with positive refracting power. For power variation from the wideangle side to the telephoto side, all the lens groups move toward the object side on the optical axis and for focusing, the 2nd lens group G2 moves toward the object side on the optical axis. The movement track of the focusing lens group is composed of the movement track for focusing and movement track for power variation correction and the quantity of rotary movement of the distance ring for the focusing of the focusing lens group is equalized to the rotation of the rotary lens barrel prescribed by the movement track for the focusing.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a zoom lens, and particularly to its focusing method, from a so-called inner focus or rear focus method by moving some of the lens groups within the lens system, to a focusing method for focusing the lens group on the object side. Regarding the front ball feeding method by movement.

0002

2. Description of the Related Art In recent years, various focusing methods other than the front lens extension method have been proposed in order to make zoom lenses more compact, higher in performance, and even higher in magnification. However, when using a focusing method other than the front lens extension method, the amount of extension changes as the focal length changes.
This has the disadvantage that so-called manual focusing becomes impossible. In addition, in a zoom lens in which the front lens is moved out, and the overall length changes with the focal length, a similar problem arises in that the amount of movement for focusing changes. Therefore, the present applicant applied for Japanese Patent Application Publication No. 63-16380.
In step 8, by using the locus of movement of the focusing lens group when changing the magnification, so-called manual focusing is possible even if the amount of extension necessary for focusing differs depending on the state of changing the magnification or the focusing group. proposed a method to do so.

This method means that when a predetermined locus of movement for zooming is expressed as a variable, the rotation angle of the rotating lens barrel for defining the amount of movement of each lens group in the optical axis direction, All movement trajectories are set so that the amount of rotational movement for focusing of the focusing lens group on the movement trajectories is equal for a constant object distance in any zooming state. there were.

0004

[Problems to be Solved by the Invention] The above-mentioned method is a highly practical method that enables manual focusing when the amount of feeding is different, which was conventionally considered impossible. However, when applied to an actual optical system, the rotation angle required for focusing is generally much smaller than the rotation angle required for zooming.

[0005] Furthermore, in view of the hardware structure, it is desirable to cut a plurality of cams corresponding to the locus of movement of a given movable lens group, taking into account eccentricity and operability of the lens group. For this reason, the magnitude of the rotation angle required for zooming is subject to certain limitations. Therefore, if the rotation angle required for focusing is considerably smaller than the rotation angle required for zooming, the rotation angle for focusing due to the hardware structure will necessarily be considerably smaller.

In this case, if the rotation angle for focusing of the focusing lens group and the rotation angle of the distance ring match, that is, the rotation mechanism for focusing of the focusing group and the distance ring are directly connected. When the distance ring is turned for focusing, the shooting distance at which the subject is in focus changes rapidly, making it difficult to achieve fine focusing. From the above, in reality, it is necessary to increase the rotation angle of the distance ring, and it is also necessary to enlarge the rotation angle for focusing the focusing lens group and transmit it to the distance ring. However, since the helicoid mechanism cannot be used to expand rotation into rotation, it is necessary to newly provide a cam mechanism or differential mechanism for expansion. This causes a looseness factor due to the hardware structure, resulting in a decrease in focusing accuracy and deterioration in operability.

Furthermore, since focusing is achieved by moving the focusing lens group on a locus that moves during zooming, the position of the imaging point at any focal length and shooting distance is the same as the depth of focus. It has the disadvantage that it can change internally. Therefore, by adding an enlarging mechanism to this, the amount of displacement of the imaging point position is enlarged, and the depth of focus may be exceeded. From the above points, it is difficult to provide a zoom lens with high focusing accuracy and good operability, and to achieve this, it is necessary to improve the precision of the hardware, leading to an increase in costs.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to secure a sufficiently large rotation angle of a rotating lens barrel for focusing movement of a focusing lens group without intervening a special enlarging mechanism on the lens barrel structure,
By directly transmitting the rotation amount of the distance ring and at the same time converting the movement trajectory of each lens group so as to suppress the displacement of the imaging point due to focusing to a sufficiently small value, focusing accuracy is high and operability is improved. Our goal is to provide a good zoom lens.

[0009]

[Means for Solving the Problems] In the present invention, in a zoom lens system having a plurality of lens groups including a focusing lens group having both magnification changing and focusing functions, the movement locus of the focusing lens group is focused. It is formed by combining the focusing movement trajectory and the magnification correction movement trajectory, and the rotational movement amount of the distance ring for focusing the focusing lens group is determined by the rotational movement amount of the rotating lens barrel defined by the focusing movement trajectory. It is configured to be equal to the rotation angle.

Specifically, first, the movement trajectory of a plurality of lens groups that move on the optical axis for zooming is determined by the rotation angle of the rotating lens barrel to define the amount of movement of each lens group in the optical axis direction. When expressed as a variable, the rotational movement amount for focusing on the rotating lens barrel of the focusing lens group is calculated. If the amount of rotational movement can be used as the rotation angle of the distance ring, consider manual focus and, if necessary, convert the movement trajectory so that the deviation of the imaging point is sufficiently small.
The rotation angle of the focusing lens group is transmitted to the range ring.

Next, if the amount of rotational movement of the focusing lens group for focusing is too small or too large to be used as the rotation angle of the distance ring, the amount of rotational movement is expanded or reduced. For this purpose, the movement trajectory of the focusing lens group during zooming is divided into a focusing movement trajectory and a zooming correction movement trajectory. Furthermore, when performing focusing using this focusing movement trajectory, the shape of the focusing movement trajectory is determined so that the amount of displacement of the imaging point is sufficiently small at any focal length and arbitrary shooting distance. . Finally, the movement trajectory for magnification correction and the movement trajectory of each lens group not involved in focusing are converted according to the focusing movement trajectory to determine the final movement trajectory.

In order to carry out the above method and to sufficiently reduce the amount of deviation of the imaging point, it is preferable that all movement trajectories of the movable lens group be made nonlinear. In addition, in the present invention, the focusing movement locus and the magnification correction movement locus refer to a focusing movement cam and a magnification movement cam formed on a rotating lens barrel that rotates around the optical axis of the lens system. Corresponding to the magnification correction moving cam, the movement locus of the focusing lens group is formed as a composite movement form due to the rotation of both cams.

[0013]

[Operation] According to the structure of the present invention, the rotation angle on the rotary lens barrel for focusing the focusing lens group is ensured to be sufficiently large, and the distance lens can be directly focused without using any other magnification mechanism. Therefore, it is possible to eliminate the backlash caused by the magnifying mechanism and the error caused by the optical arrangement. Since the rotation angle of the distance ring can be made sufficiently large, it is possible to improve the operability during manual focusing. Furthermore, since the shape of the divided focusing movement trajectory is determined so that the amount of deviation of the image forming point is sufficiently small, it is possible to significantly improve the focusing accuracy.

[0014]

EXAMPLES The present invention will be specifically explained below based on examples. As shown in FIG. 1, the zoom lens of Example 1 includes, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a positive refractive power. Consisting of four lens groups, the fourth group G4 has refractive power, all lens groups move toward the object side along the optical axis when changing the magnification from the wide-angle side to the telephoto side, and the second lens group G2 moves toward the object side during focusing. It is configured to move on the optical axis toward the object.

To explain the structure of each lens group, the first lens group G1 with positive refractive power includes a negative meniscus lens L1 with a convex surface facing the object side, a biconvex lens L2 cemented to this, and a biconvex lens L2 with a convex surface facing the object side. The second lens group G2 with negative refractive power is composed of a negative meniscus lens L4 with a surface with a stronger curvature facing toward the image side.
, a double-concave negative lens L5, a convex meniscus lens L6 cemented thereto, and a positive meniscus lens L7 with its convex surface facing the object side, and the third lens group G has a positive refractive power.
3 consists of a biconvex positive lens L8, a biconvex positive lens L9, and a negative lens L10 cemented thereto, and a fourth lens group G4 with positive refractive power includes a positive lens L11 and a biconvex positive lens L.
12, and a negative meniscus lens L13 having a surface with a stronger curvature facing toward the object side. Note that the aperture S is the third lens group G3 on the object side of the third lens group G3.
It is arranged integrally with.

Table 1 shows the specifications of this zoom lens. f
represents the focal length, and FN represents the F number. In Table 1, r is the radius of curvature of each lens surface, d is the distance between lens surfaces, and n
represents the refractive index of each lens, V represents the Abbe number, and the subscript number represents the order from the object side. The middle row of Table 1 shows the values of each coefficient representing the shape of the aspheric surface formed on the object side lens surface (r6) of the object side lens L4 in the second lens group G2.

The height of the aspherical surface from the optical axis is h, the distance from the tangential plane of the apex of the aspherical surface at h is x, the conic constant is k, the second order, the fourth order, the sixth order, etc. The 8th and 10th aspherical coefficients are A2, A4, A6,
When A8 and A10 and the paraxial radius of curvature is r,
It is expressed by an aspherical equation as shown below.

[0018]

[Math 1]

In the middle row of the lens system specification table in Table 1,
From left to right: conic constant k, 2nd, 4th, 6th, 8th, and 10th aspheric coefficients A2, A4, A6
, A8, and A10 are listed in order. Note that E-n in the value of the aspheric coefficient represents 10-n.

The bottom row of Table 1 shows six positions (f=36.
0, 50.0, 60.0, 70.0, 85.0, 103
．． 0) shows the spacing between each lens group. FIG. 1 also shows the locus of movement of each lens group during zooming. Here, the amount of movement in the optical axis direction and the rotation angle of the rotating lens barrel are selected so that the movement locus of the first lens group G1 during zooming becomes a straight line.

[0021] First, in this zoom lens,
The amount of movement ΔX of the second lens group G2 in the optical axis direction for focusing on a subject at a shooting distance of 0.85 m is calculated. Next, the rotation angle φ of the rotating lens barrel corresponding to this value ΔX is determined from the movement trajectory shown in FIG. Note that the movement trajectories g1, g2, g3, and g4 of each lens group from the first lens group G1 to the fourth lens group G4 in FIG. 2 are essentially the same as the movement trajectories shown in FIG. In the figure, the locus of movement of each group is drawn such that 1 mm of movement of the first lens group G1 in the optical axis direction for zooming corresponds to a rotation angle of 2 degrees of the rotating lens barrel. Table 2 shows ΔX and φ determined in this way. For example, from Table 2, focal length f = 103m
The amount of movement of the second lens group in the optical axis direction required to focus on a subject at a shooting distance of 0.85 m at m is 4.
08 mm, and the corresponding rotation angle is 54.4°.

Further, Table 3 shows specific numerical values of the movement locus shown in FIG. 2. In addition, the second lens group G2 is used for focusing by extending the locus it moves during zooming, so it is extended to the telephoto side by the rotation angle necessary for focusing, and its value is It is written. Table 2 shows that the rotation angle φ of the rotating lens barrel required for focusing in each focal length state does not match, so if the zoom is changed when the lens is focused at a certain short distance, focusing scan will be required again. , manual focusing is not possible. Therefore, the rotation angle φ required for focusing so that manual focus is possible
The locus of movement shown in FIG. 2 or Table 3 must be changed so that the distances are equal at each focal length.

FIG. 3 shows the movement locus g1 of each lens group shown in FIG. 2 so that the rotation angle φ for focusing required to focus on an object at a shooting distance of 0.85 m is the same at each focal length. , g2, g3, and g4. Table 4 lists numerical values indicating the specific shape. The configuration up to this point is based on the earlier application (Japanese Patent Application Laid-open No. 163808/1983).
The basic configuration is similar to that disclosed in . In Table 4, the total rotation angle of the second lens group G2 including zooming and focusing is approximately 100°. This is because it is assumed that three sets of the same cam will be cut over a 360° circumference, taking into account eccentricity, etc.

From Table 4, the rotation angle φ required for focusing is 100.
7133°−73.0744°≒27.64°. Considering that the rotation angle φ from infinity to close range in manual focus would need to be at least 50° to 60°, the focusing rotation angle would be 27.6.
This means that sufficient manual focusing accuracy and operability cannot be obtained at 4°.

Therefore, in order to directly enlarge this rotation angle, the second lens group G, which is a focusing lens group, is used as described above.
Consider dividing the movement trajectory of 2 into a focusing movement trajectory and a magnification correction movement trajectory. As mentioned above, the total rotation angle of the second lens group, which is the focusing lens group, including zooming and focusing is 1
00° to 110°, and in this example, both the rotation angle from the wide-angle end to the telephoto end during zooming and the rotation angle for focusing were set to 55°. This makes it possible to improve the operability and precision of both focusing and zooming. In other words, it is originally desirable for the rotation angle for focusing to be larger, but since there is a limit to the combined rotation angle for focusing and zooming (110° in this example), if the rotation angle for focusing is made larger, This is because if it is too large, the rotation angle for changing the magnification becomes smaller, and the operability of changing the magnification deteriorates.

Now, regarding the method of determining the focusing movement locus gF, specifically, as shown in FIG. 4, the focal length f=f'(
f'=36,50,60,70,85,103), and the coordinates on the focusing movement trajectory at infinite shooting distance are (X; θ)
= (X f=f', R=un; θf=f'), ΔX f=f', R
= 850, the coordinates corresponding to focal length f = f' and shooting distance R = 0.85 m are (X; θ) = (X f
=f', R=un+ΔX f=f', R=850; θ
It is sufficient to determine the focusing movement locus so that f=f'+55). Here, R=un is the shooting distance at infinity (unend
lich).

When obtained in this way, the representative point (X; θ) = (0; 0) of the focusing movement locus is f = 36, R =
(X; θ) = (1.0365; 55) represents f = 103, R = un and f = 36, R = 850. Then, (X; θ)=(5.1165;110) represents f=103 and R=850. However, with this method, when the shooting distance R = 850 mm, the desired amount of extension is obtained, so the imaging plane is kept constant, but when it comes to an arbitrary shooting distance, the imaging point is kept near the imaging plane. There is no guarantee whether or not this is the case.

Therefore, in this embodiment, the shooting distance R=1
．． The focusing movement locus was determined using an optimization method so that the deviation amount of the imaging point was small even at 0, 1.5, 2.0, 3.0, and 5.0 m. In other words, the amount of displacement of the imaging point at focal length fi and shooting distance Rj is DX
When ij, the single evaluation function Φ is

[0029]

[Math 2]

[0030] However, gij is a load indicating the relative importance of DXij m = n = 6 fi = 36, 50, 60, 70, 85, 103 mm
Rj =0.85, 1.0, 1.5, 2.0, 3
．． 0,5.0 m(1), and mainly θ f=f' (f at R=un) to minimize equation (1).
Focusing is performed by changing the θ coordinates of i = 36, 50, 60, 70, 85, 103) and φ R = R' (rotation angle for focusing required to focus on each shooting distance) as variables. The focus movement trajectory was determined.

Table 5 shows a numerical table representing the focusing movement locus obtained as described above. Then, the focusing movement trajectory g2F and the magnification correction movement trajectory g2Z of the second lens group G2 as the focusing group, which are determined according to the relationship between the rotation angle θ (ANGLE) and the focal length shown in this table, are included. All movement trajectories are shown in Figure 5. In addition, the second lens group G2
The movement trajectory is the focusing movement trajectory g2F (0<θ<110
°) and the magnification correction movement trajectory g2Z (0<θ<55°) correspond to cam grooves formed in completely different rotating lens barrels, but they are written together here to make it easier to understand both trajectories. and showed. Table 6 shows a numerical table representing the movement locus g2Z for magnification correction of the second lens group G2.
Table 7 shows a numerical table showing the movement trajectories of the third lens group G3 and the fourth lens group G4.

Here, the focusing movement locus g2F and the magnification correction movement locus g2Z of the second lens group G2 are both within the range of rotation angle 0<θ<55° used for zooming. The movement form of the second lens group G2 is determined by the movement trajectory obtained by combining the trajectories, and this trajectory coincides with the trajectory of movement during zooming. Therefore, in reality, the movement locus for zoom correction is determined by subtracting the focusing movement locus from the movement locus during zooming of the focusing lens group before division.

Next, FIG. 6 shows the synthesized movement trajectory in this magnification change, in other words, the movement trajectory before division in the final sense, and Table 8 shows the numerical values representing the movement trajectory. Therefore, in Table 8, the relationship between the amount of movement of each lens group and the focal length is the same as in Tables 3 and 4, except for the rotation angle. As can be seen from FIG. 5 or 6, according to the present invention, when the focusing movement locus is determined so as to keep the deviation amount of the imaging position small, the movement locus of all the movable lens groups is adjusted to the lens barrel rotation angle. It becomes non-linear.

FIG. 7 is a diagram for explaining the movement locus g2Z for magnification correction and the movement locus g2F for focusing of the second lens group G2 as the focusing lens group in the embodiment. First, it is assumed that the rotating lens barrel rotates from the wide-angle end (the upper end of FIG. 7) by a rotation angle of θ f = f' in a state where the photographing distance is infinite, and the magnification is changed to the focal length f = f'. At this time, the focusing lens group rotates on the rotating lens barrel by θ=θ f=f', and moves by XF = . At the same time, move along the movement trajectory for magnification correction in the direction of the optical axis.
H = XZ −XF Move. Then, this is combined in terms of hardware structure, and the focusing lens group moves on the optical axis by XH +XF =XZ, thereby contributing to variable magnification.

Next, the in-focus state, that is, the focal length f=f'
Let us consider focusing from an infinite shooting distance to a shooting distance R=R'. If the rotation angle of the rotating lens barrel corresponding to the photographing distance R=R' is φ R=R', then from FIG. 7, the focusing lens group moves on the focusing movement trajectory (X f=f', R=un; θ f=
f') to (X f=f', R=R'; θ f=f'
+φ R=R'). Therefore, the focusing lens group moves along the optical axis ΔX=Xf=f', R=R'-Xf=f', R=
Focus is achieved by moving by un.

Table 9 shows the focal length f=3 when focusing using the focusing movement locus (Table 5) determined in this example.
Shooting distance R in each zooming state of 6, 50, 60, 70, 85, 103 mm = 0.85, 1.0, 1.5
, 2.0, 3.0, 5.0 m, the rotation angle of the rotating lens barrel (range ring) for focusing, and the actual extension amount ΔX of the focusing lens group corresponding to this rotation angle. DX), and further Δ
It shows the amount of displacement (BF) of the imaging point when X is given.

The upper row of Table 9 shows the amount of displacement (BF) of the imaging point for various shooting distances R in each zooming state, and the middle row shows the amount of displacement (BF) of the imaging point for each shooting distance R. It shows the rotation angle of the rotating lens barrel (distance ring). Note that this focusing rotation angle is selected such that there is no displacement of the imaging point at the wide-angle end and the telephoto end. In addition, the lower row shows the actual extension amount Δ of each lens group corresponding to each focusing rotation angle.
The value of X (DX) is set to focal length F = 36, 50, 60, 7
Shooting distance R = 0.85, 1.0, 1.5, 2.0, 3.0 in each zooming state of 0, 85, 103 mm
, 5.0 m. In the lower row, the leftmost number indicates the focal length F of the entire system.
The right end shows the shooting distance R, and the numbers in between these are the values of the actual extension amount ΔX (DX) for the first lens group G1, second lens group G2, third lens group G3, and fourth lens group G4, in order. It is. In addition, for any value, the case of movement toward the object side is shown as a positive value.

Table 9 shows that the amount of displacement of the imaging point at each focal length and photographing distance is extremely small, and is well within the depth of focus in any zooming state and for any object distance. Next, Table 10 shows the values of the rotation angle for focusing necessary to completely optimize the amount of displacement of the imaging point due to focusing to zero, for each zooming state and shooting distance R. This is obtained from the movement trajectory. The upper row of Table 10 shows the focal length F=36, 50, 60, 70, 85, 10
Shooting distance R = 0.85, 1 in each variable magnification state of 3mm
．． The optimal rotation angles of the rotating lens barrel (distance ring) for focusing at 0, 1.5, 2.0, 3.0, and 5.0 m are shown, and the lower row shows the rotation angle for focusing. The value of the actual extension amount ΔX (DX) of each corresponding lens group is determined by the focal length F=36,
Shooting distance R = 0.85, 1.0, 1.5, 2.
The cases of 0, 3.0, and 5.0 m are shown.

From the values in the upper row of Table 10, it can be seen that the values of the rotation angle for focusing are extremely close for the same shooting distance R, and the amount of change due to zooming is extremely small. . Therefore, even when focusing is achieved using autofocus, the amount of correction is extremely small, so it is clear that the quick response of focusing is improved. In FIGS. 8 to 10,
Regarding the embodiments of the present invention, the focal length F=36, 50, 60, 70, 85, 103 when the shooting distance is infinite
Various aberration diagrams are shown for each magnification change state of m. Also, Figure 11~
In FIG. 13, the focal length F=36, 50, 60, 7
In each zooming state of 0, 85, and 103 mm, focusing is performed by giving the focusing extension amount ΔX calculated from the focusing movement locus obtained by the present invention for the shooting distance R = 0.85 m. The figure shows various aberrations when

From these aberration diagrams, it is clear that the zoom lens according to the present invention not only maintains good performance over the entire magnification range when photographing at infinity, but also maintains good performance over the entire magnification range when photographing at close range. It is clear that excellent imaging performance is maintained. In the above embodiment, the rotation angle of the focusing lens group is 55° + 55° for zooming and focusing.
The reason for this is that it is assumed that three sets of the same cam locus are cut on the rotating lens barrel.For example, if two sets are sufficient, the rotation angle should be made larger (for example, 110°<θ<
180°), it becomes possible to further increase the rotation angle for focusing and the rotation angle for zooming.

[0041] If both the rotation angle for focusing and the rotation angle for variable magnification can be ensured to be large, it is not necessary to make the rotation angle for focusing and the rotation angle for variable magnification the same value as in the above embodiment. However, it is generally preferable to have the same angle from both a mechanical and operational point of view. Further, in this embodiment, the focusing lens group is limited to the second lens group G2, but any lens group that can be used can be used as long as it can focus, and it is not limited to a 4-group zoom lens system; It is possible to adapt to the lens.

By the way, in the above explanation, as previously proposed in Japanese Patent Laid-Open No. 63-163808 by the same applicant as the present application, in order to enable manual focusing, the focusing lens group changes the magnification when in focus. The assumption is that the vehicle moves along the trajectory of the vehicle. however,
In the present invention, by simply dividing the movement locus of an arbitrary lens group that has both a focusing function and a variable magnification function into a movement trajectory for focusing and a trajectory for magnification correction, manual focusing is made possible. can do. Therefore, the present invention can be achieved even without the premise that the focusing lens group moves along a movement locus for zooming during focusing. In other words, after determining the amount of movement Δx on the optical axis during focusing in the description of this embodiment, it is sufficient to directly determine the movement locus for focusing without determining the rotation angle φ of the rotating lens barrel. Yonaru.

For example, in the case of a so-called U-turn trajectory in which the movement locus for zooming of the focusing group is reversed during zooming, the structure of the previous application has an area where focusing is not possible. However, by dividing the movement trajectory into a magnification correction movement trajectory and a focusing movement trajectory as in the present invention,
It becomes possible to eliminate areas that cannot be focused. moreover,
The lens group that has a variable power function here does not only mean a lens group that moves for variable power, but also a lens group that is fixed on the optical axis during variable power.
Depending on the relationship with the front and rear lens groups, the lens may have a substantially variable magnification function, and the present invention also includes these functions. Therefore, it is also possible to make the movement trajectory determined by combining the focusing movement trajectory and the magnification change correction trajectory fixed with respect to the image plane when changing the magnification.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

[Table 9]

[0053]

[Table 10]

[0054]

As described above, according to the present invention, in a zoom lens system having a plurality of lens groups including a focusing lens group having both magnification changing and focusing functions, the movement trajectory of the focusing lens group can be adjusted. By dividing the movement trajectory into a focusing movement trajectory and a magnification correction movement trajectory, a sufficiently large rotation angle for focusing can be secured and the information can be directly transmitted to the distance ring, improving operability and accuracy during focusing. It is possible to increase it.

At the same time, since a hardware structural enlarging mechanism is not required, it is possible to eliminate the backlash caused by the enlarging mechanism. Furthermore, since the focusing movement trajectory is determined in such a way that the amount of displacement of the imaging point is minimized, even if the amount of movement for focusing differs depending on the magnification change state, extremely high-precision focusing can be achieved, making it an excellent lens. This enables manual focus and rapid autofocus.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a lens structure of a zoom lens system according to the present invention, and a diagram showing an example of movement trajectories for changing the magnification of each lens group.

FIG. 2 is a diagram showing a movement trajectory including zooming and focusing in the example.

FIG. 3 is a diagram showing a trajectory resulting from changing the movement trajectory shown in FIG. 2 so that the rotation angle φ for focusing to focus at a shooting distance of 0.85 m is the same at each focal length.

FIG. 4 is an explanatory diagram for determining a focusing movement locus of a focusing lens group.

FIG. 5 is a diagram showing the final movement trajectory of each lens group according to the example.

FIG. 6 is a diagram showing movement trajectories for synthesized magnification changing according to the embodiment.

FIG. 7 is a diagram for explaining the zooming and focusing operations of the focusing lens group in the present invention.

FIG. 8 is a diagram showing various aberrations when the focal length f=36, 50 mm and the shooting distance is infinite in the example.

FIG. 9 is a diagram showing various aberrations when the focal length f=60, 70 mm and the shooting distance is infinite in the example.

FIG. 10: Focal length f=85,103 mm in the example;
Diagrams of various aberrations when the shooting distance is infinite.

FIG. 11 is a diagram showing various aberrations when the focal length f=36.50 mm and the shooting distance is 0.85 m in the example.

FIG. 12 is a diagram showing various aberrations when the focal length f=60, 70 mm and the shooting distance is 0.85 m in the example.

FIG. 13: Focal length f=85,103 mm in the example;
Various aberration diagrams when the shooting distance is 0.85 m.

[Explanation of symbols of main parts]

G1...First lens group G2...Second lens group (focusing lens group) G3...
・Third lens group G4...Fourth lens group g1...Locus of variable power of the first lens group g2...Locus of variable power of the second lens group (focusing lens group) g3...Third lens Group magnification change trajectory g4...Fourth lens group magnification change trajectory gF, g2F...Focusing movement trajectory g2Z...Magnification change correction movement trajectory

Claims (2)

[Claims] Claim 1: In a zoom lens system having a plurality of lens groups including a focusing lens group having both functions of zooming and focusing, a predetermined movement locus for zooming is set in the direction of the optical axis of the lens group. When expressing the rotation angle of the rotating lens barrel for defining the amount of movement as a variable, the movement trajectory of the focusing lens group is formed by combining the focusing movement trajectory and the magnification correction movement trajectory, and A zoom lens system characterized in that a rotational movement amount of a distance ring for focusing the focusing lens group is equal to a rotation angle of a rotating lens barrel defined by the focusing movement locus. 2. The focusing movement locus along which the focusing lens group moves for focusing is such that the amount of displacement of the imaging point position is sufficiently small in any zooming state and also at any shooting distance. 2. The zoom lens system according to claim 1, wherein the shape of the zoom lens system is determined in accordance with the shape of the zoom lens system, and accordingly, all movement trajectories including lens groups not involved in focusing are set to be nonlinear.