JPH07113697B2 - Zoom lens focusing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a focusing device for a zoom lens such as a camera.

(Prior Art) In a zoom lens that performs focus adjustment by moving a movable lens in a master lens unit, the focus position of the master lens unit moves when the magnification is changed in the zoom lens unit even if the subject distance is constant. Therefore, in order to keep the focal position constant, it is necessary to calculate the focal length and automatically correct the movable lens position of the master lens unit. Examples of this method include JP-A-57-186872 and JP-A-52
As shown in Japanese Unexamined Patent Publication No. 114321 or the like, a moving range calculation circuit that incorporates the positional information of the movable lens of the master lens unit that depends on the focal length and the subject distance as a calculation formula or a table is provided to detect the focal length. The position of the movable lens of the master lens unit is corrected by using this. A digital circuit is generally used to hold the position information as a calculation formula or a table.

(Problems to be Solved by the Invention) However, when a digital circuit is used, the resolution of the analog-digital conversion circuit and the digital-analog conversion circuit affects the precision of control. Therefore, if the resolution is increased, the conversion circuit becomes complicated. Conversely, if the resolution is decreased, continuous control cannot be performed, resulting in an unsightly image.
Generally, in the automatic focus adjustment state, the focus distance and aperture information are contained in the servo loop and the focus adjustment is performed as a whole, so the image is not unsightly. Since no correction means is included, the image tends to be unsightly. Moreover, the stability of the conversion circuit is poor and the circuit cannot be simplified.

The present invention has been made in view of the above problems, and an object thereof is to provide a simple and accurate focusing device for a zoom lens.

[Structure of Invention]

(Means for Solving Problems) A focusing device for a zoom lens according to the present invention has a cam mechanism C for advancing and retracting a movable lens by rotation and a zoom ring 14 for rotating the cam mechanism C. C is the zoom ring
The zoom lens unit A formed so that the rotation angle of 14 is a logarithmic function of the focal length, the master lens unit B having the drive unit 23 that moves the movable lens forward and backward, and the applied voltage changes according to the subject distance information. Charge / discharge circuit 70 and the zoom ring 14
A sample pulse generating circuit 60 that outputs a sampling pulse that changes according to the position of the sample pulse, and a sample that holds the output of the charging / discharging circuit 70 by the sampling pulse and controls the driving unit 23 of the master lens unit B by the output. And a hold circuit 78.

(Operation) The present invention rotates the zoom ring 14 to rotate the cam mechanism C,
The cam mechanism C advances and retracts the movable lens of the zoom lens unit A. At this time, since the zoom ring 14 is graduated by the cam mechanism C in the logarithmic function of the focal length of the zoom lens unit A, the movable lens of the zoom lens unit A is the zoom ring 14.
It reciprocates with a logarithmic function for the rotation of. Then, the position of the zoom ring 14 is detected as the movable lens of the zoom lens unit A moves back and forth, and the sample pulse generating circuit 60 outputs a pulse corresponding to the position of the zoom ring 14 and applies the pulse corresponding to the subject distance information. The output changed by the discharge of the charging / discharging circuit 70 in which the voltage changes is held, and the drive unit 23 is driven by this output to drive the movable lens of the master lens unit B to adjust the focal length.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a cylindrical base cylinder, and a support portion 2 connected to the rear portion of the base cylinder 1 to the camera body via an adapter or the like.
And a cylindrical lens barrel main body 4 is attached to the front portion of the base cylinder 1 via a cylindrical fixed cylinder 3. A first group lens including first, second, and third lenses L ₁ , L ₂ , and L ₃ is provided in the front part of the lens barrel body 4 via a first group lens frame 5, and a mirror is provided. A second lens group, which is a variator composed of _fourth , _fifth , and sixth lenses L ₄ , L ₅ , and L ₆ , and a third lens group frame 7 are provided in the cylinder body 4 via a second lens group frame 6. The third lens group as a compensator composed of the seventh lens L ₇ is provided so as to be movable back and forth in the axial direction. That is, the second lens group frame 6 and the third lens group frame 7 are movably supported by a plurality of guide shafts 8 provided in parallel in the upper and lower parts of the lens barrel main body 4, and the second lens group lens Engaging elements 9 and 10 project from the upper portions of the frame 6 and the third lens group frame 7, and the engaging elements 9 and 10 are cylindrical cams concentrically and rotatably provided in the lens barrel body 4. Tube 11
Engaging with the cam grooves 11a, 11b, and an engaging member 13 projecting from an opening groove 12 in the circumferential direction of the lens barrel main body 4 is provided on the upper part of the cam cylinder 11 so as to project from the cam cylinder 11 and the cam grooves 11a, 11b. Cam mechanism C with 11b
Are configured. Further, a cylindrical zoom ring 14 is concentrically and rotatably provided on the rear outer peripheral portion of the lens barrel body 4, and an engaging element 13 of the cam barrel 11 is engaged inside the zoom ring 14. Together with the zoom lever 15 on the outside of the zoom ring 14.
Is provided, and a cylindrical movable cylinder 16 facing the outer periphery of the fixed cylinder 3 is integrally provided at the rear part of the zoom ring 14.

In the cam grooves 11a and 11b, the rotation angle of the zoom ring 14 is a logarithmic function of the focal length, that is, θ is a rotation angle, f is a focal length, and F and G are constants, θ = F logf−G Is formed.

When the zoom ring 15 is rotated by the zoom lever 15, the cam barrel 11 is rotated via the engaging element 13 engaged with the zoom ring 14, and the engaging elements 9 and 10 engaged with the cam grooves 11a and 11b. The second group lens frame 6 and the third group lens frame 7 advance and retreat in the axial direction along the guide shaft 8 via the, and advance and retract the second and third group lenses L _{4 to} L ₇ as movable lenses. It is like this.

Further, a fourth lens group including the eighth and ninth lenses L ₈ and L ₉ is provided at the rear part of the lens barrel body 4 via a fourth lens group frame 17.

In the front part of the base cylinder 1 through the fifth group lens frame 18, the tenth,
A fifth group lens including the eleventh and twelfth lenses L ₁₀ , L ₁₁ , and L ₁₂ is provided, and a cylindrical fixed barrel 19 is integrally provided at the rear portion of the fifth group lens frame 18. . In addition, the 13th and 14th lenses L ₁₃ and
A sixth lens group consisting of L ₁₃ is provided so as to be movable back and forth in the axial direction. That is, the sixth group lens frame 20 is supported by a guide shaft 21 provided in the base cylinder 1 so as to be able to move forward and backward, and an operating portion 22 is projectingly provided above the sixth group lens frame 20. A movable cylinder 25 is connected to a drive shaft 24 of a linear motor 23 serving as a drive unit provided in the base cylinder 1, and the front part of the sixth group lens frame 20 faces the fixed cylinder 19. Are provided integrally.

Then, the linear motor 23 is driven to advance / retreat the drive shaft 24 thereof, and the sixth lens group frame 20 is axially advanced / retreated along the guide shaft 21 via the actuating portion 22 to form a sixth lens group as a movable lens. It is designed to move back and forth between L ₁₃ and L ₁₄ .

Then, above the zoom lens unit A by the first to ninth lens L ₁ ~L _9, constitutes a master lens section B by tenth to fourteenth lens L ₁₀ ~L _14.

Further, a zoom ring position detecting device 31 is provided between the base barrel 1 and the zoom ring 14, and a master lens position detecting device is provided between the fixed barrel 19 of the base barrel 1 and the sixth lens group frame 20. 32 are provided.

As shown in FIGS. 2 and 3, the zoom ring position detecting device 31 includes a pair of semicircular arc-shaped electrodes 33 and 34 in the circumferential direction of the outer periphery of the fixed cylinder 3 in the front part of the base cylinder 1. Electrodes 35 which are mounted adjacent to each other in an insulating state and which have a length equal to or greater than the amount of rotation of the zoom ring 14 in the circumferential direction of the inner periphery of the movable barrel 16 at the rear portion of the zoom ring 14 are substantially semi-circular.
The electrodes 33 and 34 of the fixed cylinder 3 and the electrode 35 of the movable cylinder 16 are opposed to each other with a small gap therebetween to form two variable capacitors 36 and 37.

As shown in FIGS. 2 and 4, the master lens position detecting device 32 includes a fixed cylinder in the front part of the base cylinder 1.
A pair of cylindrical electrodes 38, 38 are attached to each other in the axial direction of the inner circumference of 19 so as to be adjacent to each other in an insulated state, and a sixth electrode is provided on the outer circumference of the movable cylinder 25 in the front part of the sixth group lens frame 20. A cylindrical electrode 40 having a width equal to or larger than the movement amount of the group lens frame 20 is attached, and the electrodes 38 and 39 of the fixed cylinder 19 and the electrode 40 of the movable cylinder 25 are opposed to each other with a small clearance, Two variable capacitors 41 and 42 are configured.

In FIG. 1, 51 is a square wave of opposite polarity φ ₁ , φ ₂
And a reference signal generating circuit for generating a triangular wave φ ₃ and a timing pulse φ _4. The square wave φ ₁ output end of the reference signal generating circuit 51 is connected to _one of the inside of the zoom ring position detecting device 31 via a resistor 52. The output end of the square wave φ ₂ is applied to the electrode 33 via the resistor 53 to the other electrode 34 inside the zoom ring position detection device 31, and the output end of the triangular wave φ ₃ is applied to the electrode 54 between the electrode 33 and the resistor 54. , 55 are connected. Further, a sample pulse generating circuit 60 is connected to the electrode 35 outside the zoom ring position detecting device 31. This sample pulse generation circuit 60 is connected from the output end of the amplifier 61 to the non-inversion input end of a zero-cross comparator composed of an operational amplifier 63 via a capacitor 62. The inverting input end of this operational amplifier 63 is grounded and Is connected to a monostable multivibrator 64.

Reference numeral 66 is a variable voltage source that is changed by the distance setting means 67, and this variable voltage source 66 is connected to the charging / discharging circuit 70. The charge / discharge circuit 70 is composed of a capacitor 72 and a resistor 73 which are connected in parallel via a switch 71 and have one end grounded. The switch 71 has an output end for the timing pulse φ ₄ of the reference signal generation circuit 51. Connected, switch 71 is closed with timing pulse φ ₄ . The charge / discharge circuit 70 is connected to the sample hold circuit 75. This sample-hold circuit 75 is connected to a switch capacitor 76, which is connected to the holding capacitor 77 whose one end is grounded, and the non-inverting input terminal of an operational amplifier 78, and which is connected to the output terminal and the inverting input terminal of the operational amplifier 78 by a voltage follower. The sample pulse generating circuit 60 is connected to the switch 76, and the switch 76 is closed by the sample pulse.

The sample hold circuit 75 is connected to the lens drive circuit 81. The lens drive circuit 81 includes an operational amplifier 82 for the drive unit 23 that drives the master lens unit B.
To the inverting input side of the operational amplifier 82, the sensor 83 that includes the master lens position detecting device 32 and outputs the position of the master lens unit B corresponding to the voltage is connected. And this lens drive circuit 81
Constitutes a servo system that advances and retracts until the voltages of the sample hold circuit 75 and the master lens position detecting device 32 become equal.

Next, the operation will be described with reference to FIG.

The image of the subject is formed on the film (imaging surface) of the camera body through the lenses L _{1 to} L ₁₄ of the first group to the sixth group.

In imaging, first, the zoom ring 14 is rotated to move the second and third lens groups forward and backward, and the fourth, fifth, sixth and seventh lenses L ₄ , which are movable lenses of the zoom lens unit A. L ₅ ,
Change L ₆ and L ₇ back and forth to change the magnification. At this time, the zoom ring position detection device 31 operates. That is, when the zoom lens is at the standard focal length S, that is, the center position of the displacement, the facing areas of the pair of electrodes 33 and 34 of the fixed barrel 3 with respect to the electrode 35 of the movable barrel 16 of the zoom ring 14 are equal to each other, and the pair of variable The capacitors 36 and 37 have the same capacitance. Then, by rotating the electrode 35 together with the movable barrel 16 of the zoom ring 14, the facing areas of the pair of electrodes 33, 34 of the fixed barrel 3 are changed, and for example, the telephoto focal length T is set to a larger magnification than in the previous state. So that one of the variable capacitors
As the capacitance of 36 increases, the capacitance of the other variable capacitor 37 decreases, and conversely, if the wide-angle focal length W is set to a smaller magnification than in the previous state, the static capacitance of one variable capacitor 36 will decrease. As the capacitance decreases, the capacitance of the other variable capacitor 37 increases, thus
The capacitances of the pair of variable capacitors 36 and 37 change in association with the displacements of the second and third lens groups, and this is output as the positions of the second and third lens groups. Then, in order to change the magnification of the zoom lens, the zoom ring 14 is rotated to rotate the second and third zoom rings.
When the group lens is moved, the zoom ring position detection device 31 outputs the moved position.

At this time, the reference signal generation circuit 51 applies a combined wave φ ₁ + φ ₃ of the square wave φ ₁ and the triangular wave φ ₃ to one electrode 33, and combines the square wave φ ₂ and the triangular wave φ ₃ to the other electrode 34. The wave φ ₂ + φ ₃ is added. When the zoom lens is at the standard focal length S, the capacitors 36 and 37 have the same capacitance, and the unbalanced square wave φ ₁ and square wave φ ₂ cancel each other on _one electrode 35, and only the triangular wave φ ₃ component is present. Appears. Then, the comparator 63 of the sample pulse generation circuit 60 outputs normal rotation when the voltage of the triangular wave φ ₃ is 0 V or more, and outputs reverse rotation when the voltage of 0 V or less, and the monostable multivibrator 64
The sample pulse P _S is output when the output of the comparator 63 changes from the normal output to the inverted output, or when the inverted output changes to the normal output.

Also, when the zoom lens is at the telephoto focal length T, the facing area of the condenser 36 increases, whereas the condenser 37
Since the area facing each other decreases, the capacity of the capacitor 36 becomes larger than the capacity of the capacitor 37, and the voltage appearing on the electrode 35 and input to the comparator 63 is the triangular wave φ ₃ strongly influenced by the square wave φ ₁ . When the voltage crosses 0V and the comparator 63 changes to the normal output or from the inverted output to the normal output earlier than when the standard focal length S is set,
Sampling pulse P _T from monostable multivibrator 64
Will be output earlier.

On the contrary, when the zoom lens has a wide-angle focal length W, the facing area of the condenser 36 decreases,
Since the facing area of 37 increases, the capacitance of the capacitor 36 becomes smaller than the capacitance of the capacitor 37, and the voltage appearing at the electrode 35 and input to the comparator 63 becomes a triangular wave φ ₃ and a square wave φ _3.
The influence of ₂ becomes strong, the voltage crosses 0V, and the time when the comparator 63 changes from the normal output to the inverted output or from the inverted output to the normal output is the standard focal length S.
In the case of, the timing when the sampling pulse P _W is output from the monostable multivibrator 63 is delayed.

Then, when operating the above device, first, the distance setting means 67 sets the distance to a desired position, and the variable voltage source 66 is set to a voltage value corresponding to the distance.

Then, each time the timing pulse φ ₄ of the reference signal generating circuit 51 is output, the switch 71 of the charging / discharging circuit 70 is closed, the capacitor 72 is charged, and the switch 71 is opened.
As shown in the figure, the electric charge charged in the capacitor 72 is discharged by the RC circuit including the capacitor 72 and the resistor 73, and the voltage decreases exponentially. Further, in the sample hall circuit 75, the switch 76 is closed by the sample pulse from the sample pulse generating circuit 60, and the voltage of the capacitor 72 at that time shown in FIG. 7 is held by the holding capacitor 77, and the voltage follower circuit is operated. The same voltage is output from the output terminal of the constituent operational amplifier 78 and input to the non-inverted input terminal of the operational amplifier 82.

At this time, a relatively high voltage is applied to the holding capacitor 77 in the case of the telephoto focal length _T that outputs the sampling pulse P _T soon after the discharge of the capacitor 72 is started, and conversely in the case of the slow sampling pulse P _W , on the contrary. It becomes a low voltage. In the case of the sampling pulse P _{S having} the standard focal length S, the sampling pulse P _S has an intermediate value.

Regarding the master lens portion B, when the master lens portion B is at the center position, the facing areas of the electrodes 38 and 40 and the facing areas of the electrodes 39 and 40 are equal, and the capacitances of the variable capacitors 41 and 42 are equal. Are equal. When the master lens unit B advances, the facing area between the electrode 38 and the electrode 40 increases and the facing area between the electrode 39 and the electrode 40 decreases, so that the capacitance of the variable capacitor 41 is larger than that of the variable capacitor 42. Will increase. On the contrary, when the master lens portion B is retracted, the facing area between the electrodes 38 and 40 decreases and the facing area between the electrodes 39 and 40 increases, so that the capacitance of the variable capacitor 41 becomes larger than that of the variable capacitor 42. Less. Then, as in the case of the zoom lens unit A, the position of the master lens unit B is set to the variable condenser 4
Replace it with a displacement of 1,42 and convert the position into a voltage value.

Then, the voltage indicating the position of the zoom lens unit A is input to the normal input side of the operational amplifier 82, and is input to the inverting input side of the sensor 83 indicating the position of the master lens unit B. Then, the drive unit 23 advances and retreats the master lens unit B in a direction in which the difference between the two inputs is eliminated by the operational amplifier 82, and the focus is adjusted.

The reason why the cam mechanism C of the zoom lens unit A is set by a logarithmic function and the CR circuit is used is as follows. If x is the lens extension amount, a is the subject distance, and f is the focal length, then x = f ² / a (1) Further, the rotation angle θ of the zoom ring 16 is a logarithmic function of the focal length f. In the zoom lens set as described above, θ = Flogf−G or θ = F′lnf−G (F, F ′, and G are constants) (2), and by transforming the equation (2), lnf = ( θ + G) / F '... (3) Therefore, f = e ^{(θ + G) / F'} ... (4).

From equations (1) and (4), On the other hand, the discharge voltage Ex after t seconds in the CR discharge circuit is Ex = E ₀ e ^{−t / CR} (11) When the initial value is E ₀ , the discharge voltage Ex after t seconds in the CR charge circuit is Becomes Ex = E ₀ (1-e ^{−t / CR} ) = E ₀ −E ₀ e ^{−t / CR} (12), and if E ₀ −Ex is E _X , then substituting it in equation (12) , E _X = E ₀ e ^{−t / CR} (13), and equations (6) and (13) can be expressed by similar functions.

Therefore, from equations (5) and (13), If each constant is set so that
Can be calculated as the change in the terminal voltage E _X.

Further, the sensor 83 is not limited to one that determines the voltage based on the discharge time of the capacitor 72 using the charge / discharge circuit 70 as described above, but may be one that outputs the voltage from the capacitance of the variable capacitors 40 and 41.

Also, if the distance setting means 67 is switched to a distance measuring device, an automatic focus adjustment operation is possible.

Further, the charging / discharging circuit 70 is not limited to the circuit shown in the figure, and the same operation can be obtained by using a known CR charging / discharging circuit.

〔The invention's effect〕

According to the present invention, the charge charged in the charge / discharge circuit is discharged, the sample pulse circuit outputs the sample pulse at different time depending on the position of the lens, and the discharge time is changed to output the voltage corresponding to the position. Therefore, a simple, inexpensive and accurate focusing device can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a focusing device for a zoom lens according to the present invention, FIG. 2 is a longitudinal sectional view of the device, and FIG.
FIG. 4 is a perspective view of a part of FIG. 2, FIG. 4 is a perspective view of a part of FIG. 2, FIG. 5 is a flow chart, FIG. 6 is a time-voltage relationship diagram of a discharge circuit, and FIG. FIG. A: Zoom lens part, B: Master lens part, C ...
… Cam mechanism, 14 …… Zoom ring, 23 …… Drive unit, 60 …… Sample pulse generation circuit, 70 …… Charge / discharge circuit, 75 …… Sample hold circuit, L ₄ , L ₅ , L ₆ , L ₇ … ... Zoom lens section A
Second lens group, third lens group, and L ₁₃ and L ₁₄ as movable lenses of
The sixth lens group as the movable lens of the master lens unit B.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location G03B 13/36 (72) Inventor Tomio Fujimori 1-21-17 Takashima, Suwa-shi, Nagano Chinon Co., Ltd. (72) Inventor Akihiko Seiya 1-217 Takashima, Suwa, Nagano Chinon Co., Ltd. (72) Inventor Katsuhiko Otsuki 1-217 Takashima, Suwa, Nagano Chinon Co., Ltd. (56) References JP-A-60-143309 (JP, A) JP-A-52-114324 (JP, A)

Claims (1)

[Claims] 1. A cam mechanism for advancing and retracting a movable lens by rotation and a zoom ring for rotating the cam mechanism, wherein the cam mechanism is formed such that a rotation angle of the zoom ring is a logarithmic function of a focal length. A zoom lens unit, a master lens unit that has a drive unit that moves the movable lens forward and backward, a charge / discharge circuit that changes the applied voltage according to the subject distance information, and a sampling pulse that changes according to the position of the zoom ring. A zoom lens comprising: a sample pulse generation circuit for outputting; and a sample hold circuit for holding the output of the charge / discharge circuit by the sampling pulse and controlling the drive unit of the master lens unit by the output. Focusing device.