JP2732564B2 - Focus adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a focus adjusting device, and more particularly, to an optical device such as a camera, the focus adjusting operation of a focus lens comprising a rear group lens according to a zooming operation. And a focusing device for automatically performing the focusing. [Prior Art] There are a method of driving a front lens group and a method of driving a rear lens group as focus adjusting means for a still camera, a video camera, and the like. In the latter case, the rear group lens is smaller and lighter than the front group lens, so less power is required to move the lens.Focus is performed in a shorter time because the rear group lens moves less than the front group lens. There are a number of excellent advantages, for example, the need for helicoids for driving the front group lens is eliminated, and the cost of manufacturing the lens can be reduced. Although the latter has many advantages as described above, the former drive method is adopted in a camera having a zoom lens (Japanese Utility Model Publication No. 54-14496,
See JP-B-51-17045). [Problems to be solved by the invention] The reason is that in the method of driving the rear group lens,
This is because the focus position changes with the movement of the zoom lens during manual focusing. That is, there is no problem if the zoom lens moves at a speed that the rear group lens can follow at the time of autofocusing. Will be shifted. Therefore, in order to solve this, the cams that determine the movement amount of the zoom lens and the rear group lens are correlated, and the rear group lens moves following the movement of the zoom lens. However, it is difficult to actually provide such a cam mechanism in the lens barrel because the configuration becomes very complicated. Further, even if the above-described cam mechanism can be provided, sufficient working accuracy cannot be obtained, and high focusing accuracy cannot be obtained over the entire zooming region. Accordingly, if the rear group lens can be moved in response to zooming even during manual focusing without providing such a complicated cam mechanism, the advantage of the camera having a zoom lens can be obtained as described above. Many rear group driving methods can be realized. The present invention has been made in view of the above-described circumstances, and has a simple configuration without using a complicated mechanism or the like, and automatically sets a focus lens including a rear group lens at a focusing corresponding position according to a set distance. It is an object of the present invention to provide a focus adjustment device that can maintain a focused state even during a zooming operation by moving the focus adjustment device. [Means and Actions for Solving the Problems] A focus adjusting device of the present invention includes a lens system including at least a zoom lens and a rear group lens movably provided for focusing adjustment, and Setting distance signal generating means for generating a signal corresponding to the setting distance related to the lens system,
A zoom lens driving unit configured to indirectly drive the displacement of the zoom lens via a driving source that responds to an operation of an operating element, a zoom sensor that detects a position of the zoom lens, and the zoom lens driving unit Detecting means for detecting a lens driving speed, and a positional relationship between the zoom lens and the rear lens group in various focusing distances in a focused state at that distance are previously set inside, and the zoom lens detected by the zoom sensor A control signal for tracing the position and the rear group lens position in the focused state corresponding to the set distance according to the output signal of the set distance signal generating means based on the internal setting, and moving the rear group lens to that position. A rear-group lens control circuit that outputs a signal, and drives the rear-group lens in response to a control signal from the rear-group lens control circuit. Rear lens drive means, and the zoom lens drive means and the rear lens drive means adjust the lens drive speed of the zoom lens drive means detected by the detection means to the in-focus state by the rear lens drive means. The rear lens group is configured so as not to exceed a speed at which the rear group lens can follow the lens while holding the lens. [Embodiment] Hereinafter, the present invention will be described based on an illustrated embodiment. FIG. 1 is a block diagram of a focus adjusting device showing one embodiment of the present invention. The focus adjusting device shown in FIG. 1 is applied to a video camera, and an imaging lens barrel 1 of the camera has a front lens group 2, a zoom lens 3, a diaphragm 4, a rear lens group 5, and the like. Thus, while the front lens group 2 is fixed to the fixed portion of the lens barrel 1, the rear lens group 5 can be moved in the optical axis direction for focus adjustment.
That is, as shown in FIG. 2, the rear lens group 5 has a pin 7a integrally provided on the lens holding frame 7 and a stepping motor 8
Is engaged with the feed screw 9 connected to the output shaft 8a of
When the stepping motor 8 is driven, the lens holding frame 7 moves the guide member 10 provided along the optical axis direction in the direction of arrow A or B by the pitch of the feed screw 9. The stepping motor 8 is driven by a control signal from the control circuit 11. When the rear lens group 5 reaches the infinity position, as shown in FIG. 2, the light-shielding portion 7b provided integrally with the lens holding frame 7 is moved by the zero point sensor 12 composed of a photo interrupter. The reference position (zero point) is detected. The output of the zero point sensor 12 is input to the control circuit 11. As shown in FIG. 3, an operation ring 6 engraved with a distance scale is rotatably provided on the outer periphery of the lens barrel 1 with an appropriate frictional force between the operation ring 6 and a fixed frame. The operation ring 6 is not mechanically connected to an optical element or the like in the lens barrel 1, and its own rotation causes the distance scale supported by the index 1a to serve as a set distance signal generating means. The electric signal is electrically read by the distance scale sensor 13, and the read electric signal is input to the control circuit 11. The electric signal in the above is a set distance signal indicating a distance set using the distance scale as a standard. The distance scale sensor 13 is configured, for example, as shown in FIG. That is, in FIG. 4, a conductive contact 14 is fixedly provided inside the operation ring 6, and the conductive contact 14 is
A thin-film conductor 15 formed on the outer periphery of the fixed frame of the lens barrel 1 along the rotation direction and a thin-film resistor 16 formed substantially in parallel with and similar to the conductor 15 are in sliding contact with each other. . conductor
15 is grounded, and the resistor 16 is connected to the input terminal of the control circuit 11. Then, the operation ring 6 is set to “auto” which exceeds the “closest” scale position or the “infinite” scale position.
(Not shown), and when the resistance value changes according to the rotation position of the operation ring 6,
A / D of the control circuit 11 according to the change of this resistance value
The electric signal input to converter 17 changes. The A / D converter 17 converts the electric signal from the distance scale sensor 13 into an A / D signal.
The digital signal is converted and sent to the microcomputer 18 according to the distance scale. When the operating ring 6 is set to the "auto" rotation position, the conductive contact 14 does not contact the resistor 16 but only the conductor 15, so that the conductor 15 and the resistor 16
The gap is in an open state, and the input information to the control circuit 11 at this time is “auto”. That is, when the control circuit 11 reads "auto", the control circuit 11
Numeral 11 switches the control of the stepping motor 8 for driving the rear group lens 5 from manual focus by the operation ring 6 to auto focus. When the zoom switch 3 operates the zoom switch 32,
The zoom sensor can be moved in the optical axis direction by a motor 20 driven by a control signal from a lens control unit 19.
The focal length is read by 21, and the read electrical signal is input to the lens control unit 19. The zoom sensor 21 is a position sensor including, for example, a potentiometer, a photo sensor, and the like. The iris 4 may be operated either manually or automatically. The iris value is read by the iris sensor 22, and the read electric signal is input to the lens control unit 19. ing. The subject light transmitted through the optical system of the lens barrel 1 forms an image on an imaging surface of an imaging device 23, and is photoelectrically converted by the imaging device 23 into a video signal. The video signal is processed by a camera circuit 24. Extracted as a video signal. The luminance signal of the video signal is input from the camera circuit 24 to the auto focus processing circuit 25. This auto focus processing circuit
25 performs signal processing such as differentiation from the luminance signal to extract harmonic components, compares the phase of the output of the same harmonic component with the phase of vibration of the rear lens group 5 during autofocusing, It is a well-known circuit (for example, Japanese Patent Application Laid-Open No. 56-116007), which determines either the back focus or focus and sends a focus state signal to the control circuit 11. Further, the control circuit 11 receives, for example,
A clock signal that is an integral multiple of 15 Hz is input. When this clock signal is input to the control circuit 11, a necessary pulse is sent from the control circuit 11 to the stepping motor 8 based on the frequency of 15 Hz, and the stepping motor 8 drives the auto focus or the manual focus based on the pulse. Do. As shown in FIG. 5, the control circuit 11 includes a storage unit 30, an operation unit 28, and a step number calculation unit 29 in the microcomputer 18. The storage unit 30 stores a characteristic curve representing a proper position of the rear group lens 5 determined by the focal length and the photographing distance, a ROM (read only memory).
It is. The calculation unit 28 includes an output of the distance scale sensor 13 input from the A / D converter 17, an output of the zoom sensor 21 input from the lens control unit 19, and the aperture sensor 22.
Is read, and an appropriate position of the rear lens group 5 is calculated from the characteristic curve stored in the storage unit 30.
Further, at the time of auto focus, the output of the auto focus processing circuit 25 is guided to calculate this. The output of the calculation unit 28 is guided to a motor drive circuit 31 and the number of steps calculation unit 29 causes the rear group lens 5 to output.
The number of steps is always counted where the position is. Further, a distance display device 27 for displaying a distance at the time of auto-focusing is connected to the calculation unit. The characteristic curve stored in the storage unit 30 in the microcomputer 18 is, for example, as shown in FIG. In FIG. 6, the horizontal axis represents the rear group lens 5.
The vertical axis indicates the amount of movement of the zoom lens 3 on the basis of the imaging surface of the image sensor 23. As is apparent from FIG. 6, when the zoom lens 3 is at the position of “T (telephoto)”, the rear group lens 5 is “infinity”, “1 m”, “0.
Each position of focus that fit length position of 5m "a _1, a _2, a ₃
It is. Further, when the zoom lens 3 is in position "S (standard)", the focus that fits in the rear lens group 5 is each distance position is a position b _1, b _2, b _3, respectively, the zoom lens 3 when in the position of "W (wide-angle)", the rear lens group 5 are each the position c _1, c _2, c ₃ of in focus to the respective distance position. That is, when the rear lens group 5 is focused on “infinity”, a change in the focal length due to the movement of the zoom lens 3 from “W” to “T” is substantially “く”. As shown by the characteristic curve l ₁ in the shape of “
Needs to be changed. Also, the rear group lens 5
In order to focus on “1 m” and “0.5 m”, respectively, the characteristic curve l ₂ , which has a substantially “<” shape, with respect to a change in the focal length due to the movement of the entire zoom lens 3. l it is necessary to change the feeding amount of the rear group lens 5 as indicated by _3. The shapes of the characteristic curves l ₁ , l ₂ , l ₃ are all different. For the distance positions other than these three distance positions “infinity”, “1 m”, and “0.5 m”, the extension amount of the rear group lens 5 is the above-mentioned characteristic curve.
Needless to say, the characteristic curve between l ₁ , l ₂ , and l ₃ follows a characteristic curve (not shown) having a different shape from these. Although it is difficult for the cam mechanism to extend the rear group lens 5 that differs depending on the focal length and the photographing distance, as represented by the characteristic curves l ₁ , l ₂ , and l ₃ , the characteristic curves In the area between l ₁ , l ₂ , l ₃ and each of these curves, each characteristic curve (not shown) corresponding to the focal length and the photographing distance is stored in the storage unit 30, so that the feeding amount by the stepping motor 8 is obtained. Can be controlled in a complicated manner. Lens 5 after the addition area between the characteristic curve l ₁ of the "infinite" characteristic curve l ₃ of the "close" is set so as not to be controlled. Still further, according to the present invention, the focal length is set exclusively by operating the zoom switch 32 as an operation element, and the motor 20 is driven by a control signal from the lens control unit 19 to drive the zoom lens. 3 is controlled to a position of a desired focal length. In the above description, the zoom lens driving means, which is a component of the present invention, includes the zoom switch 32 and the lens control unit 1.
9 (part) and a motor 20. The rear lens control circuit is a microcomputer of the control circuit 11.
The rear lens drive means includes a motor drive circuit 31 of the control circuit 11 and the stepping motor 8. As described above, in the present invention, the zoom lens driving unit and the rear group lens driving unit can follow the rear group lens while maintaining the in-focus state by the lens driving speed V by the zoom lens driving unit. Speed Vo. For this purpose, for example, a motor having a smaller capacity (small torque) than the motor 8 for driving the rear lens group is applied as the motor 20 for driving the zoom lens, and the displacement transmission system for both of them is decelerated with respect to the motor 20. The ratio may be made much larger than that for the motor 8. Alternatively, the lens control unit 19 is configured to detect the moving speed V of the zoom lens 3 based on the output signal of the zoom sensor 21 and to perform control such that this speed does not exceed the speed Vo that can be followed. Is also good. This can be realized, for example, by incorporating a known power control circuit in the circuit of the lens control unit 19 to control the power supplied to the motor 20 in response to the output signal of the zoom sensor 21. Next, the operation of the focus adjustment device configured as described above will be described. In the case of manual focusing, when the operation ring 6 is rotated to set the index 1a to a desired distance scale, an electric signal corresponding to the set distance scale is input to the control circuit 11 rather than the distance scale sensor 13. On the other hand, as described above, the focal length is set by operating the zoom switch 32 as an operation element. The motor 20 is driven by a control signal from the lens control unit 19, and the zoom lens 3 is driven to a desired position. It is controlled to the position of the focal length. Then, the position of the zoom lens 3, that is, the focal length information is detected by the zoom sensor 21 and the lens control unit 19
Read by. Also, the information of the aperture 4 is converted into an electric signal by the aperture sensor 22 and is converted into a lens control unit.
Read by 19. The electric signal from the distance scale sensor 13 is converted to an A / D converter 17
The A / D conversion is performed, and the photographing distance information set at the time is input to the arithmetic unit 28 of the microcomputer 18 of the control circuit 11, and the focal length information and the aperture information are transmitted from the lens control unit 19 to the arithmetic unit 28. Is input, the calculation unit 28 reads these pieces of information and refers to them as each characteristic curve which is the content of the storage unit 30. Then, when the proper extension position of the rear lens group 5 is traced from the characteristic curve suitable for the input information, the arithmetic unit 28 sends a signal corresponding to this to the motor drive circuit 31 to rotate the stepping motor 8 to the appropriate position. . As a result, when a zooming operation is performed at a certain shooting distance, the rear group lens 5 moves in response to this operation so as to always maintain a focused state. As described above, in the present invention, the zoom lens driving unit and the rear group lens driving unit can follow the rear group lens while maintaining the in-focus state by the lens driving speed V by the zoom lens driving unit. Speed Vo. Therefore, the in-focus state is always maintained automatically even if the zooming operation is performed. When the focus adjusting device is set to the auto focus state, the operation ring 6 is rotated in the direction of arrow C as shown in FIGS. )) Position. Then, at this time, the control circuit 11 is switched to perform a control operation for auto focus, and the control circuit 11
The stepping motor 8 causes the rear group lens 5 to vibrate alternately in the optical axis direction along arrows A and B (see FIG. 2) by a pulse having a frequency of 15 Hz as a reference. Since the rear lens group 5 vibrates in the optical axis direction, the optical path length fluctuates minutely.
The level of the high-frequency component included in the luminance signal input to the autofocus processing circuit 25 fluctuates slightly. The fluctuation waveform (modulation signal) of this high-frequency component is minimized in the in-focus state, and the phase of the modulation signal is inverted by 180 ° between the front and rear pins. When the arithmetic unit 28 is input to the arithmetic unit 28, the arithmetic unit 28 provides the motor drive circuit 31 with a signal for causing the stepping motor 8 to vibrate forward and backward with the same amplitude around the focal point. Since this amplitude is performed in consideration of the aperture information, that is, the depth of field, the rear group lens 5 does not change when it is actually stationary at the focal point. In this in-focus state, a display signal is sent from the calculation unit 28 to the distance display device 27, and the distance display of the focal point is performed by a light emitting diode or a liquid crystal. The signal is shifted from the focal point, and the signal of the front focus or the rear focus from the auto focus processing circuit 25 is calculated by the arithmetic unit of the control circuit 11.
When guided to 28, the arithmetic unit 28 gives a signal to the motor drive circuit 31 to move the stepping motor 8 toward the focal point while oscillating the stepping motor 8. That is, a signal oscillating with a large amplitude toward the focal point and with a small amplitude in the opposite direction is applied to the stepping motor 8, whereby the rear lens group 5 moves toward the focal point. Note that the speed at which the zoom lens 3 moves by the motor 20 during autofocusing is lower than the speed at which the rear lens group 5 moves toward the focal point, so that the autofocus operation can always follow. The distance scale sensor 13 in the above embodiment converts a distance scale into an electric signal by using a change in resistance value. In addition, for example, the distance scale sensor 3 shown in FIG.
3, or a distance scale sensor 43 shown in FIG. 8 may be used. As shown in FIG. 7, the distance scale sensor 33 includes a 3-bit photo sensor 34 integrally attached to the operation ring 6 and the outer periphery of the fixed frame of the lens barrel 1 along the rotation direction for each bit. Reflector partially pasted
35, 36, 37, and the lead wire of the photo sensor 34 is connected to the microcomputer 18 of the control circuit 11.
It is connected to the. Therefore, in the distance scale sensor 33, the photo sensor 34 is positioned at a position corresponding to the amount of rotation of the operation ring 6.
The microcontroller 18 reads the presence or absence of the reflectors 35, 36, 37 based on the presence or absence of reflected light, converts this to an electrical signal, and
Therefore, the distance scale is read into the microcontroller 18 as a digital signal. As shown in FIG. 8, the distance scale sensor 43 is a 3-bit conductive contact integrally attached to the operation ring 6.
44, and thin-film conductors 45 to 48 formed on the outer periphery of the fixed frame of the lens barrel 1 along the rotation direction for each bit, of which the conductor 45 is grounded, The conductors 46 to 48 are connected to the input terminal of the microcomputer 18 while the voltage Vcc is applied by the resistors 51 to 53. Accordingly, in the distance scale sensor 43, the conductive contact 44 is connected to the conductor 46 in accordance with the rotational position of the operation ring 6.
~ 48 and the conductor 45 are short-circuited or released,
Each of the conductors 46 to 48 becomes low level "L" (ground) or high level "H" (voltage Vcc), and the distance scale is inputted to the microcomputer 18 as a 3-bit digital signal. Although the distance scale sensors 33 and 43 shown in FIGS. 7 and 8 are of a 3-bit configuration, actually, in the telephoto (T) state, the distance from 0.5 m to ∞ (see FIG. 6) is reduced. It is desirable to have a configuration of about 7 bits so that it can be divided into 80 to 100. [Effects of the Invention] As described above, according to the present invention, with a simple electric circuit configuration without using a cam mechanism or the like, the focusing state according to the set distance is always performed regardless of the zooming operation. Can be maintained. Further, the lens driving speed by the zoom lens driving means is detected, and the lens driving speed is maintained by the rear lens driving means so that the in-focus state is maintained and the rear lens group does not exceed the following speed. Therefore, at the time of the zooming operation, it is possible to perform the zooming in which the subject can be more easily visually recognized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an electric circuit of a focus adjusting device showing one embodiment of the present invention, and FIG. 2 is a cross section showing a driving portion of a rear group lens in FIG. FIG. 3, FIG. 3 is a perspective view showing the appearance of the operation ring in FIG. 1, FIG. 4 is a schematic configuration diagram showing an example of the distance scale sensor in FIG. 1, and FIG. FIG. 6 is a block diagram showing a part of the function of the control circuit in FIG. 1, FIG. 6 is a characteristic curve diagram for lens control stored in the storage unit in FIG. 5, and FIG. It is a schematic structure figure showing other examples of a scale sensor. 3. Zoom lens 5 Rear group lens 8 Stepping motor 11 Control circuit 13 Distance scale sensor 19 Lens control unit 20 Motor 21 Zoom sensor 32 Zoom switch

Claims (1)

(57) [Claims] A lens system including at least a zoom lens and a rear group lens movably provided for focusing adjustment; setting distance signal generating means for generating a signal corresponding to a setting distance related to the lens system; A zoom lens driving unit configured to indirectly drive the displacement of the zoom lens via a driving source that responds to an operation of a child; a zoom sensor for detecting a position of the zoom lens; and a lens by the zoom lens driving unit Detecting means for detecting a driving speed; and a positional relationship between the zoom lens and the rear lens group in various focusing distances in a focused state at the distance is previously set inside, and a zoom lens position detected by the zoom sensor And raising the rear lens group position in the in-focus state corresponding to the set distance based on the output signal of the set distance signal generating means. A rear-group lens control circuit for tracing based on internal settings and outputting a control signal for moving the rear-group lens to that position; and the rear-group lens in response to a control signal from the rear-group lens control circuit And a rear lens driving means for driving the zoom lens. The zoom lens driving means and the rear lens driving means are arranged so that the lens driving speed of the zoom lens driving means detected by the detecting means is adjusted by the rear lens driving means. A focus adjustment device, wherein the focus adjustment device is configured to maintain a focus state so that the rear group lens does not exceed a speed that can be followed.