GB1579518A

GB1579518A - Automatic focusing system in zoom lens camera

Info

Publication number: GB1579518A
Application number: GB1164178A
Authority: GB
Original assignee: Bell and Howell Japan
Current assignee: Bell and Howell Japan
Priority date: 1977-03-23
Filing date: 1978-03-23
Publication date: 1980-11-19
Also published as: JPS53116828A

Description

(54) AUTOMATIC FOCUSING SYSTEM IN ZOOM LENS CAMERA (71) We, BELL & HOWELL JAPAN, LTD, NIHON BERU-HAUERU KABUSHIKI KAISHA of 10-1, 2-chome, Misumicho, Higashimurayama-City, Tokyo 189, Japan, a corporation organized under the laws of Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a camera having a zoom lens and an automatic focusing device.

The camera may be a movie camera. In the past, zoom lenses have been focused by movement of a heavy large diameter front objective. The weight of such objectives and their distance from the body of the camera has required that large and powerful motors be provided to adjust them for automatic focus. Such focusing systems require heavy auxiliary batteries or quickly exhaust conventional built-in batteries.

It is an object of this invention to provide an automatic focus system for a zoom lens of a camera, which does not require extra high capacity or large and heavy batteries to power the motor for the automatic focusing of the lens.

Improvements are continuously being made to optical instruments such as cameras having a focusable objective lens. One of the more recent series of improvements is an automatic focusing system for adjusting the focus of the lens to subject distance corresponding to the distance of the camera to remote subjects in the field of view of that lens. Typically, an automatic focusing system may use the principle of spatial image correlation wherein a scene imaged by a first auxiliary optical system is scanned by a sensor and the image therefrom is correlated electronically by another sensor with an image from a fixed auxilary optical system. Such an automatic focusing system has electronics for evaluating the light bundles from images passed through those optical systems and impinging on sensor arrays. Electronic circuits are used to control power for a motor for driving the focusing cell of an objective lens in accordance with the relationship of the images transmitted by the optical systems. Correct focus of the objective lens occurs when the images from the optical systems are coincident; under such conditions the position of the scanning optical system is related to the position of the objective lens.

Certain of the automatic focusing systems, as described in recently issued United States patents, can be mass produced, are not unduly complex, bulky, or expensive, and are reliable for use in optical instruments or cameras for the mass market. Such systems include a scanning means, which moves an optical axis to sweep an image across a light sensitive array, and which is connected with another similar array of a distance detector.

One of the optical axes is fixed relative to the rangefinder and camera lens and the other is moveable so as to scan along the other optical axis. An automatic rangefinder of the type generally described in U.S. Patent 4,002,899 assigned to Honeywell, Inc., and called the Honeywell Visitronics module responds to the two optical systems that bring light from the subject to a detector having a pair of photo sensitive arrays. The module is responsive to the fact that the axes of the optical systems are aligned with one another and directed toward the same subject. Such alignment causes the detector to generate a peak pulse which pulse can be used to adjust the focus of the camera lens.

Rangefinding is accomplished by triangulation of the correlated images from the fixed axis and from the scanning axis relative to the position of the scanning axis at peak pulse.

By means of suitable electronic circuitry the timing of the peak signal can be converted to a control signal for the focusing motor.

The invention consists in a camera with a zoom lens system adapted to be used for zooming and automatic focusing which includes an optical axis normally extending from said camera through the lens system front objective; a focusing and zooming system having a variator lens mounted between said front objective and said camera for movement along the optical axis of the lens system for zooming, a compensator lens mounted between said variator lens and said camera for movement along the optical axis of the lens system for focusing, an automatic focusing detection means including a photo sensitive means being cyclically subjected to light from a subject to detect a peak signal for providing a pair of first signals corresponding to the distance of the subject from the camera and for designating a preferred focused position for said compensator lens along said optical axis for optimum focus, a variator lens position indicating means operatively connected to said variator lens for providing a second signal correspondingto the position of the variator lens along the optical axis, circuitry for receiving said first pair of signals and said second signal to compare the preferred position of the compensator lens to the actual position of said variator lens and for providing a third signal corresponding to a modified preferred focused position of the compensator lens along the optical axis relative to the camera and to the instantaneous position of said variator lens, and compensator lens positioning means responsive to said third signal for positioning said compensator lens along said optical axis, whereby automatically focusing and zooming is achieved.

Thus it will be seen that an automatic focusing camera is disclosed which includes a system for moving the elements of the lens system of a zoom lens which are near the camera body. More particularly the control and movement of the variator lens group for zooming and the compensator lens group for maintaining focus is disclosed, whereby zooming and focusing may be accomplished without use of complicated mechanical systems for the combined movements of variator and compensator or without requiring excess battery power for movement of the heavier and larger front objective when focusing. When focusing with any lens that is close to the camera (e.g. the compensator) the front lens is fixed while the focusing is performed thereby permitting a simplified low power motor arrangement and simple mechanical connection to the focusing lens.

The variator is moved for zooming and the compensator is moved to correct backfocus during zooming and to refocus during auto focusing.

In order to make the invention clearly understood, reference will now be made to the accompanying drawings which are given by way of example and in which: Fig. 1 is a schematic diagram of an automatic focusing system and the electronic control circuitry which controls the movements of the variator lens group and the compensator lens group during zooming and focusing; and Fig. 2 is a schematic diagram of another automatic focusing system and electronic control circuitry which includes feedback to the optical scanner and which adjusts the positions of the variator lens group and the compensator lens group during zooming and focusing.

A movie camera is disclosed with a zoom lens capable of automatic focus by movement of the lens system closest to the camera body instead of the front objective. As a result the system is more efficient because the heavy large front objective is fixed during automatic focusing and the focusing system need only move a smaller lens or group of lenses which is closer to the camera body.

The variator lens group is used for zooming and the compensator lens group is moved for focusing during zooming. The relationship between variator lens group movement and compensator lens group focusing during zooming is known and can be automatically accomplished, but the automatic focusing system is arranged to also move the compensator for focus adjustment in response to changes in the subject distance.

Figures 1 and 2 diagrammatically illustrate systems for moving the lighter, smaller lenses closer to the camera body for the purpose of focusing. In those figures, each system is laid out with the front focusing lens 11 at the left and the prime lens 14b at the right, disposed therebetween are moveable lenses 12, 13 and 14a. To the extent that the systems of Figures 1 and 2 are identical the components will be identified with the same reference numbers. In Figures 1 and 2, lens 12 is a variator lens and will be designated the second lens group; it may be composed of a single lens or a series of lens elements cemented or held together. Similarly, the lenses 14 are a compensator lens group and it will be generally designated as the fourth lens group as it may be composed of a single lens or a series of lens elements cemented or held together. Lens 13 is a collimation lens and is referred to as the third lens group as it too may be composed of a single lens or a number of lens elements cemented or held together. In Figures 1 and 2, 14a is a compensator and 14b is a prime lens. Compensator 14a is moved by a rack 18 driven by a pinion 17 along the optical axis of the lens system. A motor 19 is drivingly connected to pinion 17 so as to move rack 18 in accordance with signals from a motor control circuit 20.

Figures 1 and 2 schematically show an external rangefinding automatic focus detection system 30. System 30 has a motor control circuit 20 which is responsive to a calculating circuit 16. The motor control circuit 20 can include a switching relay for supplying power to the motor 19 to turn it for focus adjustment of the compensator lens 14a according to the signal input from the calculating circuit 16. The input for the calculating circuit 16 comes from an automatic focusing detector 43.

Detection is accomplished by establishing two optical paths designated 31 and 32; 32 is the scanning optical path. That is to say that, there is a scanning mirror 35 mounted for pivotal oscillatory movement by an eccentrically mounted disk or cam 39 driven by a belt and pulley 38. Optical path 32 varies and intersects optical path 31 over a short range located somewhere between near focus and infinity thus transmitting a varying image. Optical path 31 is fixed and is aligned substantially parallel to the optical axis of the camera taking lens such that when the images of optical paths 31 and 32 coincide with one another the distance of the subject can be determined and used as a parameter for adjusting the focus setting of the taking lens by moving lens 14a. Detection of image coincidence is accomplished by comparing images transmitted via the optical paths 31 and 32 to a pair of identical photo detectors located within a module 43 such as the Honeywell Visitronics module. Mirrors 36 and 34 are used to reflect the optical paths 31 and 32 for alignment with module 43. Optical path 31 includes a mirror 33 which is fixed to align its axle with mirror 34 for reflection through auxiliary lens 41 into module 43. Similarly, scanning mirror 35 aligns its image from optical path 32 with mirror 36 for reflection through auxiliary lens 42 into module 43.

When the image from optical path 32 is in coincidence with the image from optical path 31 a peak correlation signal is produced by module 43 and is selectively transmitted to the calculating circuit 16.

The correlation signal is sensed on a periodic basis for purposes of knowing the relative position of the scanning mirror 35 to the location of the moveable lens groups.

In Figure 2, only scanning mirror 35 is pivotally mounted on shaft 37. Shaft 37 is connected to gear 47 which is engaged with pinion 48 such that rotation of pinion 48 causes gear 47 to rotate which also rotates shaft 37. Scanning mirror 35 is mounted on shaft 37 for limited pivotal movement.

Therefore, rotation of gear 47 and shaft 37 changes the range or aspect over which scanning mirror 35 may rotate shifting toward near or far focus as a function of the position of the lens adjustment.

The position, aim or relative range for scanning mirror 35 is sensed in the following manner; cam 39 has a nib 44 which activates a phase detector switch arm 45 once per revolution of cam 39 for the systems of Figures 1 and 2. The switching provided by nib 44 is a function of the rotation of cam 39. More particularly, as focus of the lens is adjusted to be nearly that of perfect focus, the aim of scanning mirror 35 toward the subject changes to a lesser degree. The switch arm 45 acts to establish a threshold for monitoring the peak correlation signal once per revolution of cam 39, and for establishing a datum or reference pulse which is time related to the aim of the scanning mirror 35. An electronic phase detector circuit 46 receives the pulses from switch 45 and acts to time the consideration of signals from module 43 by the calculating circuit 16. The aim of mirror 35 is directly related to the timing of the peak signal from module 43. The peak signal is periodically reviewed by the calculating circuit 16 and the amount that the lens is out of focus is determined at least once per cycle so that corrections in the focus of the lens and the alignment (Figure 2 only) of scanning mirror 35 can be made.

The lens is zoomed by combined movements of the variator lens group 12 and the compensator 14a. The variator lens group 12 is carried by a zooming control external of the lens so that the operator can move the variator lens group 12 axially along the optical axis changing the image field from wide angle to telephoto and back. A position indicating device 15 is connected to the variator lens group 12 whereby a position signal is generated in accordance with the location of the variator lens group 12. The variator position signal is transmitted to the calculating circuit 16 and is applied thereto to obtain an output signal therefrom which not only accounts for focus adjustment as already described but also includes compensator 14a movement as necessary during zooming, to maintain proper focus by calculating circuit 16 which compares the relative positions of the variator lens 12 to that of the compensator lens 14a, with the position of the compensator lens being defined as the point of reference during automatic focusing and the position of variator lens 12 as the point of reference during zooming.

More particularly, the auto focus input from automatic focusing detector 43 and phase detector circuit 46 which delineates a preferred focused position for the compensator 14a, to the calculating circuit 16 and the zoom position signal or the relative position of variator 12 by variator position indicating device 15 which produces an output indicative of the position of lens 12 along the optical axis and which acts as an input to the calculating circuit 16 are combined and issue as a combined correction or output signal to adjust the compensacor 14a.

A motor control circuit 20 is connected in circuit with the output of calculating circuit 16 and controls a motor 19 which drives a pinion 17 for moving a rack 18 to which the compensator 14a is mounted, Figures 1 and 2.

Compensator 14a is moved axially along the optical axis of the lens to correct for zooming and focus; such that no matter where the zoom position of the lens or the object distance of the subject, the lens is kept in precise focus adjustment.

Consequently, the positioning of the compensator 14a is known to the calculating circuit 16 since the end position to which it is driven is known. Readjustment of the compensator 14a in response to movement of the variator lens group 12 or to the signal of the automatic focus system 30 begins at the known position of the compensator.

More particularly, a position detecting device could also be connected between the rack 18 and the calculating circuit 16 thus simplifying the design of the calculating circuit 16.

In Figures 1 and 2, the automatic focusing position of the compensator lens 14a is a function of the position of the variator lens 12. Proper focus, as controlled by compensator 14a is dependent upon the focal length or zoom position of variator lens 12. In Figure 2, position indicating devices 15 and 51, in the form of variable resistors in a bridge circuit or the like, monitor the relative positions of lenses 12 and 14a respectively, which information is furnished to and is interpreted by calculating circuit 16. As described above, the relative position of compensator 14a is continuously monitored by phase detector circuit 46.

The system of Figure 2 is different in that the readjustment of the focus position of compensator 14a is also considered by the calculating circuit 16. That is to say that, pinion 48 drives a rack 49 which translates across a detecting device 51; the latter giving a position signal relative to the aim or range of scan of the scanning mirror 35.

A motor 50 is connected to drive pinion 48 for shifting the range or aspect of the mirror 35. The scan position signal is applied to the calculating circuit 16 to modify the output signal therefrom so that the motor control circuit 20, figure 2, will be capable of adjusting the power supplied to motors 19 and 50.

Thus, the readjustment of compensator 14a by motor 19 is accompanied by a readjustment of the aspect of scanning mirror 35 by motor 50.

WHAT WE CLAIM IS: 1. A camera with a zoom lens system adapted to be used for zooming and automatic focusing which includes an optical axis normally extending from said camera through the lens system front objective; a focusing and zooming system having a variator lens mounted between said front objective and said camera for movement along the optical axis of the lens system for zooming, a compensating lens mounted between said variator lens and said camera for movement along the optical axis of the lens system for focusing, an automatic focusing detection means including a photo sensitive means being cyclically subjected to light from a subject to detect a peak signal for providing a pair of first signals corresponding to the distance of the subject from the camera and for designating a preferred focused position for said compensator lens along said optical axis for optimum focus, a variator lens position indicating means operatively connected to said variator lens for providing a second signal corresponding to the position of the variator lens along the optical axis, circuitry for receiving said first pair of signals and said second signal to compare the preferred position of the compensator lens to the actual position of said variator lens and for providing a third signal corresponding to a modified preferred focused position of the compensator lens along the optical axis relative to the camera and to the instantaneous position of said variator lens, and compensator lens positioning means responsive to said third signal for positioning said compensator lens along said optical axis, whereby automatic focusing and zooming is achieved.

2. A camera as claimed in claim 1, wherein said compensator lens positioning means includes a rack connected to said compensator lens, a pinion, and a controlled motor for driving said pinion, which motor is operatively connected to said circuitry means and is adapted to drive said pinion for movement of said rack along a path parallel to said optical axis.

3. A camera as claimed in claim 1, wherein said zoom lens is a variator, compensator and collimator zoom lens system, and said compensator lens is moved in response to movement of said variator lens during zooming and is moved in response to movement of the subject during automatic focusing and wherein said responsive movements are not exclusive but are cumulative.

4. A camera as claimed in claim 1, further including means for shifting the cyclical orientation of said photo sensitive means to enhance the relative level of detection of said automatic focusing means, means for detecting the cyclical orientation of the photo sensitive means and for generating a corresponding position signal, and control means receiving said position signal and said third signal and for modifying the latter.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. optical axis of the lens to correct for zooming and focus; such that no matter where the zoom position of the lens or the object distance of the subject, the lens is kept in precise focus adjustment. Consequently, the positioning of the compensator 14a is known to the calculating circuit 16 since the end position to which it is driven is known. Readjustment of the compensator 14a in response to movement of the variator lens group 12 or to the signal of the automatic focus system 30 begins at the known position of the compensator. More particularly, a position detecting device could also be connected between the rack 18 and the calculating circuit 16 thus simplifying the design of the calculating circuit 16. In Figures 1 and 2, the automatic focusing position of the compensator lens 14a is a function of the position of the variator lens 12. Proper focus, as controlled by compensator 14a is dependent upon the focal length or zoom position of variator lens 12. In Figure 2, position indicating devices 15 and 51, in the form of variable resistors in a bridge circuit or the like, monitor the relative positions of lenses 12 and 14a respectively, which information is furnished to and is interpreted by calculating circuit 16. As described above, the relative position of compensator 14a is continuously monitored by phase detector circuit 46. The system of Figure 2 is different in that the readjustment of the focus position of compensator 14a is also considered by the calculating circuit 16. That is to say that, pinion 48 drives a rack 49 which translates across a detecting device 51; the latter giving a position signal relative to the aim or range of scan of the scanning mirror 35. A motor 50 is connected to drive pinion 48 for shifting the range or aspect of the mirror 35. The scan position signal is applied to the calculating circuit 16 to modify the output signal therefrom so that the motor control circuit 20, figure 2, will be capable of adjusting the power supplied to motors 19 and 50. Thus, the readjustment of compensator 14a by motor 19 is accompanied by a readjustment of the aspect of scanning mirror 35 by motor 50. WHAT WE CLAIM IS:

1. A camera with a zoom lens system adapted to be used for zooming and automatic focusing which includes an optical axis normally extending from said camera through the lens system front objective; a focusing and zooming system having a variator lens mounted between said front objective and said camera for movement along the optical axis of the lens system for zooming, a compensating lens mounted between said variator lens and said camera for movement along the optical axis of the lens system for focusing, an automatic focusing detection means including a photo sensitive means being cyclically subjected to light from a subject to detect a peak signal for providing a pair of first signals corresponding to the distance of the subject from the camera and for designating a preferred focused position for said compensator lens along said optical axis for optimum focus, a variator lens position indicating means operatively connected to said variator lens for providing a second signal corresponding to the position of the variator lens along the optical axis, circuitry for receiving said first pair of signals and said second signal to compare the preferred position of the compensator lens to the actual position of said variator lens and for providing a third signal corresponding to a modified preferred focused position of the compensator lens along the optical axis relative to the camera and to the instantaneous position of said variator lens, and compensator lens positioning means responsive to said third signal for positioning said compensator lens along said optical axis, whereby automatic focusing and zooming is achieved.