Abstract: An optical instrument equipped with a zoom lens installed in a zoom lens barrel having a lens guide arrangement for zooming up and down and focusing which includes a zooming-up guide path for guiding the lens group and positioning it in one of fixed zoom positions during zooming-up, a zooming-down guide for guiding the lens group and positioning it in one of fixed zoom positions during zooming-down, and focusing guide paths arranged parallel to one another and connect the zooming-up and zooming-down guide path in the fixed zoom position for guiding the lens group during focusing after zooming up or down to one of the fixed zoom position.

Abstract: A TV camera lens device includes a flange back length control signal for moving a master lens group to a position of the proper flange back length in accordance with the operation of a flange back length control. It further includes a macro control signal generating device for outputting a macro control signal for moving the master lens group to a preset macro position where the master lens group is to be positioned during the macro-shooting. Then, either one of the flange back length control signal and the macro control signal is made to take preference in accordance with the operation of a selector switch, and the selected control signal is input to a control circuit. Incidentally, the macro position may be relatively defined as referenced from the position of the proper flange back length.

Abstract: A camera, lens positioning mechanism and method use a lens holding member to hold a lens therein for receiving optical information that may be captured on film or digitally. The lens holding member interfaces with a ring-shaped barrel member, geared ring or the like, that when turned in one direction by a motor forces the lens holding member out, or back, depending on a slope of a cam placed on the barrel member, slot in the barrel member or the like. When driven in the single direction, the cam member on the ring barrel member, forces the lens holding member in a predetermined direction. A biasing member connected to the ring provides an opposing force that when used during a focusing operation pulls the lens holding member and cam member back to a home position without the need of a driving force from the motor. A clutch mechanism engages and disengages the driving force of the motor on the geared ring depending on whether a focusing operation, lens storage operation, or zooming operation is performed.

Abstract: A focal length detector of a camera having a zoom lens includes a brush having three sliding contacts which are electrically connected to one another; a code plate having three code patterns and a ground pattern, the code plate and the brush being moved relative to each other according to a variation of the focal length of the zoom lens; and a focal-length detecting circuit which is connected to the three code patterns and the ground pattern. The ground pattern always contacts a specific sliding contact of the three sliding contacts. The three code patterns are arranged so that the three code patterns come into contact with the remaining two sliding contacts in predetermined combinations when the code plate and the brush are moved relative to each other.

Abstract: A photographic lens includes, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of negative refractive power, wherein, during focusing from an infinitely distant object to a minimum-distance object, the first lens unit remains stationary, the second lens unit moves toward the image side, the third lens unit moves toward the object side and the fourth lens unit moves in such a way as to include a locus convex toward the object side.

Abstract: A zoom lens barrel driving system for a camera includes a driving source, a magnification controlling unit, and a focus controlling unit. The magnification controlling unit is formed with a plurality of barrels and a plurality of lens groups. The barrels and the lens groups move in an optical axis direction upon receipt of a driving power from the driving source such that magnification continuously varies. The focus controlling unit is formed by the lens groups. The lens groups repeatedly move between a near focal position and an infinite focal position in the optical axis direction in synchronization with variation in the magnification to perform a focus controlling operation.

Abstract: A zoom lens includes the first lens unit with a positive refracting power, the second lens unit with a negative refracting power, the third lens unit with a negative refracting power, and the fourth lens unit with a positive refracting power. When the magnification is changed, ranging from the wide-angle position to the telephoto position, each of the second, third, and fourth lens units is moved independently along the optical axis. In this case, the zoom lens satisfies the following conditions: Di/fw>0.65 &bgr;2w>−0.35 where Di is the maximum image height of the zoom lens, fw is the focal length of the zoom lens at the wide-angle position, and &bgr;2w is the lateral magnification of the second lens unit at the wide-angle position of the zoom lens.

Abstract: A different amount of movement is provided for the first lens unit L1 relative to the rotation angle of the drive ring 1 in at least one zoom lens section 12z-15z provided on a first cam 1d and a focus section 12f-15f corresponding to the zoom section. A different amount of movement is provided for the second lens element L2 relative to the rotation angle of the drive ring 1 in at least one zoom section 22z-25z provided on a second cam 1c and a focus section 22f-25f corresponding to the zoom section. The average inclination angle &thgr;3 of the retracting section 10s is increased to be greater than the average inclination angle &thgr;2 of the total section B2 excluding the retracting section 10s of the first cam 1d.

Abstract: A zooming optical system is provided with a plurality of lens groups that are moved to change a focal length of the zooming optical system. One of the plurality of lens groups including an aperture member has constituted to have (I) a focusing lens group that is driven to move for focusing, and (II) a image-vibration compensation lens group that is driven to move for compensating trembling of image due to a hand-vibration applied to the zooming optical system. The aperture member does not move when the focusing lens group or the image-vibration compensation lens group is driven to move.

Abstract: Disclosed is a device and method for opening and closing a barrier in a zoom camera. The device includes a connection lever fixed to a lens barrel of a focus lens group and rotated by the transmission of a rotational power of a focusing motor; and a barrier driving unit including a barrier driving lever contacting the connection lever to receive rotational force of the connection lever and a ring portion for pushing sector pins of barrier sectors in a direction to close the barrier sectors.

Abstract: A lens control apparatus drives a lens with a sine wave by means of a pulse motor and detects the position of the lens by counting the number of pulses during the driving of the pulse motor, and stores a stop phase which is reached by a rotor when the pulse motor is brought to a driving-stopped state. When the lens control apparatus is to move the lens to an initial position and initialize a counter for detecting the position of the lens, the lens control apparatus corrects the count value of the counter by using information indicative of the stored stop phase of the rotor.

Abstract: A zoom lens barrel has a stationary barrel, a rotatable cam barrel, a straight-movable barrel, a first lens component, and a second lens component. The stationary barrel is fixed to a camera body. The rotatable cam barrel is screw-engaged with the stationary barrel and moves along the optical axis while rotating about the optical axis. The straight-movable barrel is guided straight along the optical axis by the stationary barrel and is fitted to the rotatable cam barrel so as to be movable together therewith along the optical axis and rotatable independently thereof about the optical axis. The first lens component is fixed to the straight-movable barrel. The second lens component is guided straight along the optical axis by the straight-movable barrel and is cam-coupled to the rotatable cam barrel so as to be cam-driven along the optical axis by the rotatable cam barrel.

Abstract: A zoom lens barrel assembly includes an operating barrel formed with a zooming cam operative to perform zooming and focusing while turning, an inner movable barrel fixedly holding a front lens group and formed with a focusing cam which is movable axially only, an intermediate barrel capable of turning relatively to the inner movable barrel within a specified extent of angular interval, and a clutch mechanism operative to couple the intermediate barrel, during zooming, to the inner movable barrel together to restrain the intermediate barrel from turning relatively to the inner movable barrel so as thereby to shift axially the inner movable barrel through the zooming cam following a turn of the operating barrel and, during focusing, to the operating barrel together to restrain the intermediate barrel from turning relatively to the operating barrel and allow the inner movable barrel to turn relatively to the intermediate barrel so as thereby to shift axially the inner movable barrel relatively to the intermediat

Abstract: A camera for use with interchangeable lens barrels that can be attached to and detached from the camera body has a drive mechanism that provides the generating source for the drive power of drive elements inside each lens barrel built into the camera body. The connecting structure that provides a connection between the camera body and lens barrels varies according to the type of lens barrel, for example, whether the lens barrel contains a fixed focal length lens or a variable focal length lens. So, the functions realized by the drive of the drive elements from the drive mechanism vary according to the type of lens barrel.

Abstract: In a lens control apparatus, the performance does not deteriorate even if a filter is inserted and removed. Correction amounts of a focusing lens position which are necessary to eliminate an out-of-focus that is caused when, for example, a filter is inserted are actually measured at several zooming positions such as zm0, zm1, zm2, and zm3 and the results are stored into a predetermined memory such as an ROM or the like in a CPU 36 with respect to a position control of a lens. A correction amount when the filter is inserted at an arbitrary zooming position is calculated by a polygonal line approximation based on correction amounts at the several zooming positions. By adding this correction amount to the focusing lens position which is calculated in accordance with separately stored zoom tracking curve data when the filter is removed, a correct in-focus state can be obtained even when the filter is inserted.

Abstract: A varifocal mechanical correction mechanism for a lens barrel for a camera, wherein the mechanism drives a lens with a pair of cam rings for carrying out zooming and focusing functions. One of the cam rings is caused to linearly move in and out along an optical axis by a feed screw. The feed screw that has a shank portion outside a normal feed range and on a non-threaded portion of a shaft.

Abstract: A camera in which the ratio of an object to the photographing frame can be set comprises a varifocal lens in which the in-focus position is changed in accordance with the change in the focal lens and a focusing lens for correcting the focus by the varifocal lens. The size of the object is set to the desired size by using the varifocal lens, and thereafter the deviation of the in-focus point is controlled by the focusing lens. Since the zooming is carried out by using a varifocal lens, a camera can be provided in which the ratio of an object to the photographing frame can be set in a simple structure.

Abstract: An optical apparatus according to the present invention includes a cylindrical holding barrel, a lens moving mechanism including a cylindrical cam which is rotatably fitted on an outer surface of the holding barrel in such a manner that a plurality of moving lens frames held in the holding barrel are moved in an optical axis direction, a light quantity adjusting mechanism held in the holding barrel, for adjusting a quantity of light passing therethrough, lens moving mechanism driving sources for driving the lens moving mechanism, and light quantity adjusting mechanism driving sources for driving the light quantity adjusting mechanism. The lens moving mechanism driving sources and the light quantity adjusting mechanism driving sources are held in the holding barrel.

Abstract: A lens barrel and a camera system are capable of precisely calculating a photographic magnification and a field range. The lens barrel having a focusing or zooming movable lens unit is stored with effective focal length data corresponding to a position of the movable lens unit, detects the position of the movable lens unit, outputs the corresponding effective focal length data and calculates the photographic magnification and the field range. An accuracy of a calculated value is thereby enhanced enough not to cause an underexposure on the whole or the underexposure in a peripheral portion as compared with a central portion.

Abstract: An automatic focus adjusting apparatus comprises: a focus detecting circuit for detecting a focusing state and generating a signal according to the focusing state; a speed control circuit to switch a focus adjusting speed to a plurality of stages on the basis of an output of the focus detecting circuit; a depth detecting circuit to detect a depth of field; and a control circuit to change a threshold value of a speed switching point in the speed control circuit on the basis of an output of the depth detecting circuit.

Abstract: In a finder unit of the present invention, a cam plate for changing the magnification of a finder optical system is arciform and is, when disposed on a lens barrel on a camera, movable along the cylindrical lens barrel's outer periphery. Consequently, the finder unit can easily be incorporated into the camera, and contributes to reducing the size of the camera.

Abstract: An optical apparatus has an optical system incorporating a plurality of lenses including at least one movable lens. The optical apparatus detects temperature information or humidity information concerning the temperature or humidity around a structural member of the optical system other than the lenses, and performs, based on the detected information, compensation for a shift of the focal position caused by a change in the temperature or humidity around the structural member.

Abstract: An optical system controlling apparatus includes a plurality of lenses for varying an optical characteristic, a plurality of driving parts for driving the plurality of lenses, respectively, a plurality of sensors for detecting the respective states of drive of the plurality of lenses, and a controlling circuit for driving each of the driving parts on the basis of detection information provided by the sensor and controlling each of the lenses during a steady state, the controlling circuit being capable of performing initialization for the respective lenses by parallel processing during an initial state before the steady state is established.

Abstract: In a new retractable lens barrel of a type wherein a movable barrel is mounted protrudably in an optical axis direction from a fixed barrel or a camera body and filming is possible when the movable barrel is in a protruded state and comprising a movable lens of a variable power and/or focusing system, a space formed when the movable barrel is protruded from the fixed barrel or camera body is made a space in which the movable lens is movable during filming and the casing of the iris unit and a lens holder of a fixed lens are formed integrally. Because the space in which the movable lens is movable during filming is used to accommodate the movable barrel when the camera is not being used and the movable barrel is retracted, the length of the retracted lens barrel in the front-rear direction can be made short.

Abstract: A single-lens reflex camera comprises a taking lens having a zooming optical system, a finder whose angle of view is determined according to a focal length of the taking lens, and an operation member which is manually operated. In the single-lens reflex camera, the focal length of the taking lens is changed by driving the zooming optical system, and the zooming operation is controlled in response to an operation of the operation member so that the focal length of the taking lens is changed in the wide-angle direction by a predetermined amount. An angle of view corresponding to that which is seen before the focal length is changed is displayed within the finder.

Abstract: An image magnification control device for a camera. Control focal length required to maintain an image magnification constant is computed based upon defocus information detected by analyzing a light that passes through a photographic lens. In case a focal length of the photographic lens moves out of a range wherein the set image magnification can be obtained, various options, such as a shutter-release lock operation, can be executed depending upon the chosen design of the camera.

Abstract: A TV camera lens of the present invention is provided with a position-control signal generating means for outputting a position-control signal representing a position where a master lens group should be positioned, and a rate-control signal generating means for outputting a rate-control signal representing a rate at which the master lens group should be moved. A position/rate control changeover means validates one of the position-control signal generating means and the rate-control signal generating means. A control circuit drives a motor to move the master lens group according to the rate-control signal or the position-control signal which is validated by the position/rate control changeover means. The TV camera lens is also provided with a limit circuit. A limit position, at which the master lens group stops when the master lens group moves under the rate control, is set to a proper flange back length position, which is adjusted under the position control.

Abstract: An optical assembly includes a lens assembly having a lens barrel for supporting a lens along an optical axis, an optical base having an opening aligned with the optical axis, and a plurality of ramps and a corresponding plurality of reference locators circumferentially arranged around the lens assembly and the opening in the optical base in order to slide against one another. A retaining element biases the lens assembly against the optical base with the ramps and the reference locators likewise biased therebetween against each other. Consequently, the ramps and reference locators provide an arrangement for focusing the lens assembly. The optical assembly also includes a factory focus tab attached to the lens assembly and accessible during the manufacturing operation for focusing the lens assembly by moving the ramps against the reference locators, and a focus adjuster assembly accessible during user focus for focusing the lens assembly by moving the ramps against the reference locators.

Abstract: The present invention relates to an optical camera having a zoom function in which a focal length can be varied or the variation is actuated by a focal length changing member, and in particular to a camera in which a focal length is varied through a motor.The optical camera has a zoom lens operable by a rotatable zoom ring for changing the focal length thereof. An automatic focusing operation is effected by a control means when the focal length is changed so that an image of an object viewed through a viewfinder remains in focus. The zoom lens can include a motor and an in-exposure zoom control means can be provided for controlling zooming movement of the lens during an exposure operation.

Abstract: A device includes a zoom lens having a focusing lens the position of which varies according to a zooming operation, a first moving part arranged to mechanically move the focusing lens according to the zooming operation, and a second moving part arranged to move the focusing lens in such a way as to electrically correct any shift of focus that results from the movement of the focusing lens caused by the first moving part.

Abstract: In a zoom lens system in which the movement locus of a focusing lens unit is defined by synthesizing a focus cam and a zoom compensation cam, and the sensitivity of movement of an image point in association with the movement, in the direction of the optical axis, of the focusing lens unit in infinity and closest in-focus states does not vary so much, the ratio of the amount of rotation for focusing upon focusing from the infinity position to the closest distance position to the amount of rotation for zooming from the wide-angle end to the telephoto end in the focus cam is set to fall within a predetermined range, so that the sensitivity of movement of an image point in association with the movement, in the direction of rotation, of the focusing lens unit satisfies a specific condition.

Abstract: A driving device utilizes first and second driving units which drive an object when the operating speed of a manual operation member detected by a pulse signal are less than and not less than, respectively, a predetermined speed. The first driving unit drives the object based on the pulse signal and the second driving unit drives the object to a predetermined position. The second driving unit, when shifted to driving from the first driving unit, retains driving even if the operating speed falls below the predetermined speed.

Abstract: A lens barrel constructed of a cam slot, a lens cylinder, a memory means, a detecting means, a motor driving means and a control means. The cam slot has a discontinuous area formed in a portion corresponding to a parting line of a molding die used for molding. The lens cylinder ass a cam follower engaging with this cam slot. The memory means stores information indicating where the discontinuous area exists in the cam slot. The detecting means detects where the cam follower is positioned in the cam slot. The motor driving means makes the lens cylinder progress and retreat in the optical-axis direction by relatively driving the cam slot and the lens cylinder. The control means controls the motor driving means to drive the lens cylinder up to a position deviating from the discontinuous area when the cam follower is in the discontinuous area by comparing memory information of the memory mens with detection information of the detecting means.

Abstract: A photographic camera has a movable part to be driven by an electric motor. A rotary encoder generates a pulse for every predetermined angle rotation of the motor and the motor is feedback-controlled on the basis of a pulse signal consisting of a plurality of the pulses output from the rotary encoder. The pulse signal is divided by pulse number into a high-speed portion signal corresponding to a period where the motor is to be driven at a high speed and a low-speed portion signal corresponding to a period where the motor is to be driven at a low speed. The high-speed portion signal is frequency-divided, and the motor is driven at a high speed by the frequency-divided high-speed portion signal.

Abstract: A diaphragm movement device that moves a diaphragm mechanism with movement of a lens group to improve optical performance is disclosed. The diaphragm movement device includes a first lens group, a second lens group that is movable in the direction of the optical axis with the respect to the first lens group for focus and/or focal length adjustment, a diaphragm mechanism including a diaphragm blade holding ring, a diaphragm driving plate, and a diaphragm blade between the first lens group and the second lens group, and a diaphragm movement component having a protrusion and a sloped surface. An applied force member moves the diaphragm mechanism in the direction of the optical axis by a fixed amount corresponding to the movement of the second lens group in the direction of the optical axis.

Abstract: In a zoom lens system in which the movement locus of a focusing lens unit is defined by synthesizing a focus cam and a zoom compensation cam, when the sensitivity of movement of an image point in association with the movement, in the direction of the optical axis, of the focusing lens unit in a closest in-focus state is larger than that in an infinity in-focus state, the ratio of the amount of rotation for focusing upon focusing from the infinity position to the closest distance position to the amount of rotation for zooming from the wide-angle end to the telephoto end in the focus cam is set to fall within a predetermined range, so that the sensitivity of movement of an image point in association with the movement, in the direction of rotation, of the focusing lens unit satisfies a specific condition.

Abstract: A video camera apparatus includes a lens for forming an image, a camera circuit for converting the image formed by the lens into an image signal and outputting the image signal, and a controlling circuit for performing an initialization operation in which, before photography is started, information indicative of the state of the optical system is obtained and the lens is initialized, and for controlling an output signal of the camera circuit to fade the output signal in association with the initialization operation.

Abstract: There is provided a zoom lens of an inner focusing system which is capable of an auto-focusing operation and a manual focusing operation with a high precision.A zoom lens system in which a movement locus of a focusing lens unit is defined by synthesizing a focus cam and a zoom compensation cam is arranged such that a ratio of an amount of rotation for focusing from infinity to closest to an amount of rotation for zooming from wide angle to telephoto in the focus cam is set within a predetermined range so that, when the sensitivity of a movement of an imaging point with respect to a movement of the focusing lens unit in the direction of the optical axis in the closest in-focus state is larger than that in the infinity in-focus state, the sensitivity of the movement of the imaging point with respect to the movement of the focusing lens unit in the rotational direction satisfies specific conditions.

Abstract: A control method of a zoom lens camera comprising a lens system having a movable front lens group and a movable rear lens group, a first motor for moving the front lens group, a second motor for moving the rear lens group, a first pulse encoder which is adapted to control the angular position of the first motor and a second pulse encoder which is adapted to control the angular position of the second motor. In such a zoom lens camera. the difference in the image plane position between the wide-angle position and the telephoto position is measured to obtain the necessary number of drive pulses for the motors, so that the zoom adjustment and the fB adjustment can be carried out without need of a mechanical zoom adjustment or a mechanical fB adjustment.

Abstract: An automatic focus device capable of optimum focus lens driving control corresponding to the magnitude of the positional error of the focus lens. The automatic focus device specifies the target position of the focus lens based on information relating to the defocus distance of the focus lens, the velocity of the subject image, the current position of the focus lens and controls the driving power of the focus lens based on non-linear functions of the positional error defined as the difference between the target position and the current position of the focus lens.

Abstract: A shutter arrangement for a camera which includes a lens shutter, a lens group movable along an optical axis relative to the lens shutter, a first motor for opening or closing the lens shutter, a second motor for moving the lens group along the optical axis, and a first encoder for detecting a size of a diaphragm formed by the lens shutter. The first encoder comprises a first photosensor and a first rotating disk associated with the first photosensor. Also included is a second encoder for detecting an axial position of the lens group which comprises a second photosensor and a second rotating disk associated with the second photosensor. The first and second encoders are positioned to overlap as viewed in a direction of the optical axis.

Abstract: A driving mechanism for a photographic lens in a variable-focus photographic camera adapted to move back and forth, a first driving lens barrel movably received within a stationary lens barrel, and a second driving lens barrel movably received within the first driving lens barrel with driving forces separately transmitted from a common electric motor serving as a drive source and thereby to provide a so-called three-stage extension lens barrel which advantageously eliminates the necessity for incorporation of driving ring members into the stationary lens barrel and/or the first driving lens barrel as well as the necessity for constructing the stationary lens barrel and/or the first driving lens barrel in multiple structure. Such an arrangement also positively contributes to realization of a thin and compact camera.

Abstract: A miniaturized collapsible zoom camera changes viewfinder magnification in accordance with a change in the photographic magnification. The camera is equipped with a collapsible cam tube to cause a first lens group, which rotates around the optical axis, to move from a collapsed position to a position just before a minimum magnification position. Likewise, a zoom cam tube causes the first lens group, which rotates around the optical axis, to move from the minimum magnification position to a maximum magnification position. Sector gears are formed on the outer circumference of the collapsible cam tube and the zoom cam tube. Furthermore, the camera is equipped with a cam tube drive gear which cooperates with the sector gears. A drive motor causes the drive gear to rotate. Another gear cooperates only with the sector gear of the zoom cam tube while a variable power and movement mechanism causes variable power operation in the viewfinder.

Abstract: A focus detecting apparatus of the present invention comprises (a) an image projection unit which projects a first checking light through a first region out of two regions formed by splitting a space into two along a border plane including the optical axis of the objective optical system, onto the measured object to form an image of the light source thereon, and (b) an image detection unit which condenses a second checking light emerging from the image of the light source through the second region opposed to the first region with the border plane inbetween, on a light-receiving surface of a photodetector to form image of the measured object thereon. The image projection unit comprises a first converging optical system, which has a first refractive power in a first plane parallel to the border plane, which has a second refractive power substantially different from the first refractive power in a second plane parallel to the optical axis of the objective optical system and perpendicular to the border plane.

Abstract: An initial focusing mechanism for a variable-focus photographic camera having a three-stage extension lens barrel, in which a first driving lens barrel is linearly moved back and forth along linear guiding means relative to a stationary lens barrel in the direction of the optical axis and an initial position of the first driving lens barrel relative to the stationary lens barrel is adjusted by attaching or detaching a focusing member to or from the linear guiding means. The operation of initial focusing is thereby simplified. A support block is formed on a portion of the first driving lens barrel and a nut member formed with a female screw is loosely inserted into a nut holder formed in a portion of the support block followed by threading a driving screw extending in parallel to the optical axis with the female screw.

Abstract: An optical apparatus provided with a light receiving device for receiving light distributions from light beams passed through different portions of a pupil of a main imaging lens, a focus state detecting device for detecting the focus state of the main imaging lens from the positional relation between the light distributions received by the light receiving device, a decentration position detecting device for detecting the decentration position of a decenterable lens provided in the main imaging lens, a memory for memorizing inherent data of the main imaging lens which should correct the focus state detection output at each decentration position, and a calculating device for calculating the amount of movement of a focusing lens for focusing by the use of the inherent data read out from the memory conforming to a signal from the decentration position detecting device and the focus state detection output.

Abstract: A camera having an apparatus for adjusting a back focus by varying a distance between a rearmost point of lens groups of a photographing optical system and focal plane. The apparatus includes a stationary barrel that supports the lens groups and is fixed to the camera body, and a restricting mechanism that is provided between the camera body and the stationary barrel. The restricting mechanism restricts rotational movement of the stationary barrel with respect to the camera body, while allowing movement of the stationary barrel in an optical axis direction with respect to the camera body.

Abstract: A first zoom lens group, a second zoom lens group, a third zoom lens group and a fourth zoom lens group are arranged on an optical axis in that order from an object side. The first zoom lens group has a negative lens and a positive lens arranged in that order from the object side, the first zoom lens group as a whole acting as a zoom lens group having a positive focal length. The second zoom lens group has a negative lens and a positive lens arranged from the object side in that order, the second zoom lens group as a whole acting as a zoom lens group having a negative focal length. The third zoom lens group has a double concave lens and a double convex lens arranged in that order from the object side, the third zoom lens group as a whole acting as a zoom lens group having a positive focal length, the third zoom lens group being provided with a diaphragm.

Abstract: A cam mechanism for moving a lens along its optical axis is provided with a cam groove and a cam follower. The cam groove and the cam follower have different curvatures, so that the contact area between the cam groove and the cam follower remains substantially constant within a range of relative positions of the groove and the cam follower.

Abstract: A device for varying the focal length of a phototaking optical system comprises a cam member having a cam portion, a guide member having a guide portion, a driven member provided in a part of the phototaking optical system and maintained in contact with the cam portion and the guide portion, and a drive unit for moving the driven member in response to a relative movement of the cam member and the guide member, thereby continuously varying the total length of the phototaking optical system between a telephoto end position and a wide angle end position, wherein the cam member is formed by molding of a resinous material in such a manner that a parting line formed in the cam portion is not contacted by the driven member at the telephoto end position and at the wide angle end position.