Lens apparatus and TV camera

A lens apparatus includes an optical system, a lens barrel, and a weight. The optical system includes a movable lens unit. The lens barrel houses the optical system and includes a fixed barrel and a cam barrel. The fixed barrel supports the movable lens unit to be forwardly and backwardly movable along the optical axis of the optical system. The cam barrel is engaged with the movable lens unit, is supported by the fixed barrel to be rotatable around the optical axis, and is configured to forwardly and backwardly move the movable lens unit in accordance with the rotation of the cam barrel. The weight is engaged with the cam barrel and forwardly and backwardly moves along the optical axis in a direction opposite to a moving direction of the movable lens unit in accordance with the rotation of the cam barrel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2010-192991 (filed on Aug. 30, 2010), the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a lens apparatus including a movable lens unit forwardly and backwardly moving along an optical axis in a lens barrel, and a TV camera including the lens apparatus.

2. Related Art

A lens apparatus mounted in a TV camera such as an ENG (Electronic News Gathering) camera or a cine camera includes a movable lens unit, such as a zoom lens group, forwardly and backwardly moving along an optical axis in a lens barrel. The lens barrel includes a fixed barrel for supporting the movable lens unit to be forwardly and backwardly movable around the optical axis, a cam barrel supported to the fixed barrel to be rotatable around the optical axis, and an operation ring for operating the rotation of the cam barrel. The movable lens unit is engaged in the cam barrel and forwardly and backwardly moves by rotation of the cam barrel. A lens apparatus, in which the operation ring is driven by a servo motor, has been known (for example, refer to JP-A-9-80289).

When the lens barrel is slanted, torque is generated to the cam barrel due to the self-weight of the movable lens unit. If the operation ring is driven by a motor as in the lens apparatus described in JP-A-9-80289, even if the motor is loaded, and torque is generated to the cam barrel due to the self-weight of the movable lens unit, rotation of the cam barrel is prevented. However, if the lens apparatus does not include a motor, the cam barrel may be rotated so that the movable lens unit forwardly and backwardly moves.

If the friction between the fixed barrel and the cam barrel increases, even if torque is generated to the cam barrel due to the self-weight of the movable lens unit, the rotation of the cam barrel can be prevented, so that the movable lens unit can be prevented from forwardly and backwardly moving. However, a strong force is required to rotate the cam barrel, thereby deteriorating the operability to forwardly and backwardly move the movable lens unit.

SUMMARY OF INVENTION

The present invention has been made in consideration of the circumstances, and its object is to provide a lens apparatus capable of preventing movement of a movable lens unit due to the self-weight of the movable lens unit when a lens barrel is slanted.

According to an aspect of the invention, a lens apparatus includes an optical system, a lens barrel, and a weight. The optical system includes a movable lens unit. The lens barrel houses the optical system and includes a fixed barrel and a cam barrel. The fixed barrel supports the movable lens unit to be forwardly and backwardly movable along the optical axis of the optical system. The cam barrel is engaged with the movable lens unit, is supported by the fixed barrel to be rotatable around the optical axis, and is configured to forwardly and backwardly move the movable lens unit in accordance with the rotation of the cam barrel. The weight is engaged with the cam barrel and forwardly and backwardly moves along the optical axis in a direction opposite to a moving direction of the movable lens unit in accordance with the rotation of the cam barrel. The weight prevents the movement of the movable lens unit when the lens barrel is slanted so that the optical axis is slanted to the horizontal direction.

According to the present invention, the movable lens unit forwardly and backwardly moves along the optical axis due to rotation of the cam barrel. A weight also forwardly and backwardly moves along the optical axis in a direction opposite to the movable lens unit. When the lens barrel is slanted, the movable lens unit and the weight appear to forwardly and backwardly move along the optical axis in an identical direction, i.e., a forward direction or a backward direction, due to the self-weight of the movable lens unit and the weight. However, the rotation direction of the cam barrel with respect to the movement of the movable lens unit and the rotation direction of the cam barrel with respect to the movement of the weight are opposite to each other, so that the rotation of the cam barrel is prevented. Accordingly, when the lens barrel is slanted, the movement of the movable lens unit due to the self-weight of the movable lens unit can be prevented.

DETAILED DESCRIPTION

FIG. 1shows an example of a lens apparatus.

A lens apparatus10illustrated inFIG. 1includes a lens barrel11containing optical systems. The optical systems contained in the lens barrel11are largely classified into a focus optical system20, a zoom optical system22, an iris24, and a master optical system26in order from the front side.

The focus optical system20is an optical system for adjusting an object distance to adjust a focus, i.e., a focus position (focus adjustment), and includes a fixed focus lens group20A fixed at a certain position and a moving focus lens group20B supported to be forwardly and backwardly movable along the optical axis. The moving focus lens group20B moves so that the focus position varies.

The zoom optical system22is an optical system for adjusting a zoom ratio, i.e., a focus distance, and includes a ratio conversion system lens group22A and a correction system lens group22B, which are supported to be forwardly and backwardly movable along the optical axis. The ratio conversion system lens group22A moves so that the focus distance varies. The correction system lens group22B moves so that the variation of the focus position due to the movement of the ratio conversion system lens group22A is suppressed. The ratio conversion system lens group22A and the correction system lens group22B cooperatively move in accordance with a position relation predetermined by a zoom driving mechanism, which will be described hereafter.

The iris24operates iris blades to be open and closed for adjustment of a light quantity thereby varying an aperture diameter.

The master optical system26is an optical system for finally forming an image and includes a front master lens group26A and a rear master lens group26B. The front master lens group26A is fixed at a certain position. The rear master lens group26B is movably supported along the optical axis for adjustment of a back focus or other purposes.

The lens barrel11has a focus driving mechanism, a zoom driving mechanism, an iris driving mechanism, and a master driving mechanism for driving the movably supported moving focus lens group20B, the ratio conversion system lens group22A, the correction system lens group22B, the iris24, and the rear master lens group26B.

A focus ring40, a zoom ring42, an iris ring44, and a back focus adjusting ring46are rotatably disposed on the outer circumferential part of the fixed barrel11.

The focus driving mechanism is configured to enable the moving focus lens group20B to forwardly and backwardly move along the optical axis by rotational operation of the focus ring40.

The zoom driving mechanism is configured to enable the ratio conversion system lens group22A and the correction system lens group22B to forwardly and backwardly move along the optical axis by rotational operation of the zoom ring42.

The iris driving mechanism is configured to enable the iris24to be open and closed by rotational operation of the iris ring44.

The master driving mechanism is configured to enable the rear master lens group26B to forwardly and backwardly move along the optical axis by rotational operation of the back focus adjusting ring46.

In this specification, the movable lens unit means a lens moving by one driving mechanism, or an integrally or cooperatively moving lens group. In the lens apparatus10, the moving focus lens group20B, the ratio conversion system lens group22A, the correction system lens group22B, and the rear master lens group26B correspond to the movable lens unit.

Hereinafter, a mechanism for preventing movement of the movable lens unit due to the self-weight of the movable lens unit will be described. In the description, the ratio conversion system lens group22A and the correction system lens group22B will be described as an example of the movable lens unit.

FIGS. 2 and 3show a zoom driving mechanism of the lens apparatus10.

The lens barrel11includes a fixed barrel30, and a cam barrel31fitted in the fixed barrel30. The cam barrel31is rotatable around the optical axis. The zoom ring42is fitted outside the fixed barrel30to be rotatable around the optical axis.

On the inner circumferential surface of the fixed barrel30, a linear guide groove32extending along the optical axis is provided. On the cam barrel31, a cam groove33A for moving the ratio conversion system lens group22A and a cam groove33B for moving the correction system lens group22B are provided. The cam groove33A penetrates from the inside of the cam barrel31to the outside thereof.

The cam grooves33A and33B are all in a spiral form. The cam grooves33A and33B have different lead angles and they are in the same wrapping form based on the optical axis. Each of the cam grooves33A and33B partially overlaps with the guide groove32. The overlapping portion forwardly and backwardly moves along the optical axis in accordance with the rotation of the cam barrel31.

In the lens frame34A holing the ratio conversion system lens group22A, a cam follower35A is provided. The cam follower35A corresponding to the lens frame34A engages with the cam groove33A at the overlapping portion between the guide groove32and the cam groove33A. Subsequently, the cam follower35A penetrates the cam groove33A and is engaged with the guide groove32.

The lens frame34A engaging the cam follower35A into the guide groove32and the ratio conversion system lens group22A held in the lens frame34A are supported to the fixed barrel30to be forwardly and backwardly movable along the optical axis. The overlapping portion between the guide groove32and the cam groove33A forwardly and backwardly moves along the optical axis due to the rotation of the cam barrel31, so that the lens frame34A engaging the cam follower35A into the cam groove33A and the ratio conversion system lens group22A held in the lens frame34A move along the optical axis, in cooperation with the rotation of the cam barrel31.

Likewise, in the lens frame34B holding the correction system lens group22B, a cam follower35B is provided. The lens frame34B engages the cam follower35B into the cam groove33B at the overlapping portion between the guide groove32and the cam groove33B. Subsequently, the cam follower35B penetrates the cam groove33B and is engaged into the guide grove32. The lens frame34B and the correction system lens group22B held in the lens frame34B are supported to the fixed barrel30to be backwardly and forwardly movable along the optical axis, and move along the optical axis in cooperation with the rotation of the cam barrel31.

The rotation of the cam barrel31is realized by rotational operation of the zoom ring42. The zoom ring42is connected to the cam barrel31through a connection pin36penetrating from the inside of the fixed barrel30to the outside thereof. The rotation of the zoom ring42is transferred to the cam barrel31through the connection pin36. The cam barrel31is rotated around the optical axis in an integrated form with the zoom ring42.

On the fixed barrel30, a penetration hole37, which the connection pin36penetrates, is provided. The penetration hole37is extended in the circumferential direction of the fixed barrel30. The connection pin36is movable in the extended direction in the penetration hole37. The range of the rotation of the zoom ring42and the cam barrel31around the optical axis is defined by the penetration hole37.

In the zoom driving mechanism described above, a weight50is additionally provided. The weight50is in a circular shape and fitted outside the fixed barrel30to be moveable around the optical axis and forwardly and backwardly movable along the optical axis. The weight50is disposed at an empty space on the outer circumference of the fixed barrel30overlapping with the cam barrel31while escaping the zoom ring42. The weight50moves along the optical axis, in cooperation with the rotation of the cam barrel31.

In the weight50, a linear guide groove51extending along the optical axis and a spiral cam groove52based on the optical axis are provided. In the example illustrated, the guide groove51and the cam groove52penetrate from the inside of the weight50to the outside thereof. However, the grooves are preferably exposed on at least the inner circumferential surface of the weight50.

In the cam barrel31, an engaging pin53is provided. The engaging pin53penetrates from the inside of the fixed barrel30to the outside thereof to be engaged into the guide groove51of the weight50. In the fixed barrel30, a penetration hole, which the engaging pin53penetrates, is extended in the circumferential direction of the fixed barrel30. The rotation of the cam barrel31is transferred to the weight50through the engaging pin53. The weight50is rotated around the optical axis in an integrated form with the cam barrel31.

In the fixed barrel30, a cam pin55is provided. The cam pin55is engaged into the cam groove52of the weight50.

The weight50is rotated around the optical axis due to the rotation of the cam barrel31, so that the immovable cam pin55moves in a direction opposite to the rotation direction of the weight50. In this case, the weight50comes in sliding contact with the cam pin55on the inner side surface of the cam groove52. Since the cam groove52is a spiral groove based on the optical axis, the weight50moves along the optical axis.

The cam grooves33A and33B of the cam barrel31for driving the ratio conversion system lens group22A and the correction system lens group22B, and the cam groove52of the weight50for driving the weight50are different in the spiral wrapping form. In the example illustrated, when viewed at the front side (object side), the cam grooves33A and33B are in the forwardly wrapping form in the counterclockwise direction, and the cam groove52is in the forwardly wrapping form in the clockwise direction.

The ratio conversion system lens group22A, the correction system lens group22B, and the weight50move along the optical axis in cooperation with the rotation of the cam barrel31. However, since the cam grooves33A and33B and the cam groove52are different in the spiral wrapping form, the movement direction of the ratio conversion system lens group22A and the correction system lens group22B and the movement direction of the weight50are opposite to each other.

For example, if the cam barrel31is rotated around the optical axis in an arrow θ direction, the ratio conversion system lens group22A and the correction system lens group22B move along the optical axis in an arrow A direction (backwardly). The weight50moves along the optical axis in an arrow B direction (forwardly).

Conversely, the rotation direction of the cam barrel31when the ratio conversion system lens group22A and the correction system lens group22B move along the optical axis in a predetermined direction, and the rotation direction of the cam barrel31when the weight50moves along the optical axis in the same direction as that of the ratio conversion system lens group22A and the correction system lens group22B are opposite to each other.

If the lens barrel11is slanted so that the optical axis is slanted to the horizontal direction, the ratio conversion system lens group22A, the correction system lens group22B, and the weight50tend to move along the optical axis in an identical direction due to their self-weight.

For example, if the front side of the lens barrel11is lifted, the ratio conversion system lens group22A, the correction system lens group22B, and the weight50tend to move along the optical axis in the arrow A direction (backwardly) due to their sell-weight.

In that case, although the ratio conversion system lens group22A and the correction system lens group22B move in the arrow A direction, the cam barrel31is rotated in the arrow θ direction. Meanwhile, when the weight50moves in the arrow A direction, the cam barrel31is rotated in an arrow Φ direction opposite to the arrow θ direction. Accordingly, the cam barrel31is prevented from being rotated in any of the arrow θ direction and the arrow Φ direction. Also, the movement of the ratio conversion system lens group22A and the correction system lens group22B due to their self-weight is prevented.

In other words, the self-weight of the ratio conversion system lens group22A and the correction system lens group22B is converted into torque around the optical axis by the spiral cam grooves33A and33B based on the optical axis and generated to the cam barrel31. The self-weight of the weight50also is converted into torque around the optical axis by the spiral cam groove based on the optical axis and generated to the cam barrel31. The generated torque is balanced so that the rotation of the cam barrel31is prevented. Also, the movement of the ratio conversion system lens group22A and the correction system lens group22B due to their self-weight is prevented.

The ratio conversion system lens group22A, the correction system lens group22B, and the weight50move along the optical axis in cooperation with the rotation of the cam barrel31. The movement of the ratio conversion system lens group22A and the correction system lens group22B and the movement of the weight50are opposite to each other. Accordingly, when the lens barrel11is slanted, the movement of the ratio conversion system lens group22A and the correction system lens group22B due to their self-weight can be prevented.

In the lens apparatus10described above, the cam barrel31is fitted in the fixed barrel30. The zoom ring42fitted outside the fixed barrel30and the cam barrel31are connected through the connection pin36penetrating the fixed barrel30, so that the cam barrel31is rotated by the rotation operation of the connect pin36. As such, the penetration hole37of the fixed barrel30, which the connection pin36penetrates, is extended in the circumferential direction of the fixed barrel30. However, in order to maintain the strength of the fixed barrel30, the extended range is preferably less than about 90° around the optical axis.

If the extended range of the penetration hole37is about 90° around the optical axis, the range of the rotation of the cam barrel31also is about 90° around the optical axis. In that case, in order to secure the movement distance of the ratio conversion system lens group22A and the correction system lens group22B, the lead angles of the cam grooves33A and33B need to increase. As a result, when the lens barrel11is slanted, torque generated to the cam barrel31due to the self-weight of the ratio conversion system lens group22A and the correction system lens group22B also increases, so that the cam barrel31is also easily rotated. In that case, the rotation of the earn barrel31can be effectively prevented by the opposite operation of the weight50as described above.

In the above descriptions, the configuration to prevent the movement of the ratio conversion system lens group22A and the correction system lens group22B due to their self-weight has been described. However, the present invention can be applied to other movable lens units such as the moving focus lens group20B or the rear master lens group26B.

As described above, this specification describes a lens apparatus including an optical system including a movable lens unit, a lens barrel including a fixed barrel supporting the movable lens unit to be forwardly and backwardly movable along the optical axis of the optical system, and a cam barrel engaged with the movable lens unit and supported to the fixed barrel to be rotatable around the optical axis, so that the movable lens unit forwardly and backwardly moves due to the rotation of the cam barrel, as a lens barrel for containing the optical system, and a weight engaged with the cam barrel and forwardly and backwardly moving along the optical axis in a direction opposite to the movable lens unit due to the rotation of the cam barrel, as a weight for preventing the movement of the movable lens unit when the lens barrel is slanted so that the optical axis is slanted to the horizontal direction.

In the lens apparatus described in this specification, when the lens barrel is slanted so that the optical axis is slanted to the horizontal direction, torque generated to the cam barrel due to the self-weight of the weight and torque generated to the cam barrel due to the self-weight of the movable lens unit are balanced.

In the lens apparatus described in this specification, the cam barrel is fitted in the fixed barrel. The cam barrel additionally includes an operation ring fitted outside the fixed barrel and supported to the fixed barrel to be rotatable around the optical axis, and a connection member penetrating the fixed barrel to connect the cam barrel and the operation ring.

In the lens apparatus described in this specification, the weight is in a circular shape and fitted outside the fixed barrel to be supported to the fixed barrel.

In the lens apparatus described in this specification, the movable lens unit is a zoom lens group.

This specification describes a TV camera equipped with any one of the lens apparatuses that has been described.10lens apparatus11lens barrel20focus optical system20A fixed focus lens group20B moving focus lens group22zoom optical system22A ratio conversion system lens group22B correction system lens group24iris26master optical system26A front master lens group26B rear master lens group30fixed barrel31cam barrel32guide groove33A cam groove33B cam groove34A lens frame34B lens frame35A cam follower35B cam follower36connection pin37penetration hole40focus ring42zoom ring44iris ring46back focus operation ring50weight51guide groove52cam groove53engaging pin55cam pin