Video camera apparatus

Television – Camera – system and detail – Optics

Utility Patent

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Details

C348S352000

Utility Patent

active

06169578

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a video camera of the kind having a rear-focus type zoom lens in which a focus lens is disposed rearwardly of a variator lens, and particularly relates to a control method of driving the variator lens and the focus lens during a zooming operation.
2. Description of the Related Art
It has recently become necessary for a video camera or the like to have a zoom lens mounted thereon to perform one of the important functions of the camera. Among such zoom lenses, rear-focus type zoom lenses are popularly employed as they permit reduction in size.
The zoom lens of this type has generally been arranged to have variator and focus lenses interlocked with each other by a cam tube for correcting a defocused state resulting from a magnifying power varying action. However, for reduction in size and weight, the cam tube interlocking arrangement has recently come to be replaced with an electrical control arrangement wherein the variator and focus lenses are driven respectively by discrete motors and their interlocked relation is electrically controlled. Lenses having such an electrical control arrangement are now popularly in use and called electronic cam type zoom lenses.
A video camera of the kind having a zoom lens of the electronic cam type is generally arranged to have the variator lens driven by a DC motor and the focus lens by a stepping motor, to drive and control them to keep their positions in such a relation as to keep the zoom lens in an in-focus state by detecting the position of the variator lens, for example, with a potentiometer which uses a resistor.
The magnifying power varying action of the zoom lens is carried out, as mentioned above, by driving the variator lens with a variator-lens driving DC motor arid by driving the focus lens with a stepping motor in general.
Further, the variator lens is driven in such a way as to move at a constant speed by applying a preset voltage to the variator-lens driving DC motor.
In the video camera of the kind using the rear-focus type zoom lens as mentioned above, the variator lens and the focus lens are driven in a relation which is shown in FIG.
9
(
a
), wherein a reference symbol V denotes the positions of the variator lens and another reference symbol R denotes the positions of the focus lens.
When the variator lens is driven at a constant speed as shown in FIG.
9
(
c
) while keeping a relation to the focus lens as shown in FIG.
9
(
a
), the driving speed of the focus lens becomes as shown in FIG.
9
(
b
). As apparent from FIG.
9
(
b
), with the variator lens driven at a constant speed, the driving speed of the focus lens becomes extremely high at a telephoto-end position.
Compared with the DC motor, the stepping motor which is arranged to drive the focus lens greatly vibrates and makes a large noise. The vibration and noise increase with the speed of driving. Therefore, in the case of a video camera using a stepping motor for its zoom lens, the sound of driving the zoom lens tends to be recorded on a video tape as a noise through the microphone of the video camera when the stepping motor is driven at a high speed. An out-of-phase state might occur when the speed of the stepping motor comes to exceed a followable speed limit. In the event of the out-of-phase state, a predetermined relationship between the variator lens and the focus lens (relationship in which they are moved while maintaining an in-focus state) is disadvantageously interrupted to bring about a defocused state.
Further, according to the prior art arrangement described above, any attempt to retard the driving speed of the variator lens in the neighborhood of the telephoto end position of the zoom lens by simply lowering a voltage applied to the variator-lens driving DC motor tends to result in an unnatural intermittent motion of the variator lens, because of a strong adverse effect of uneven motor rotation resulting from the lowered voltage. Any video image obtained under such a condition is hardly agreeable.
Further, an attempt to solve this problem by applying a constant speed control on the basis of changes taking place in the output signal of the potentiometer is hardly feasible, because a microcomputer in charge of this specific control controls also actuators for other purposes such as control over an iris stop or the like and is hardly capable of carrying out fine control for this purpose. That attempt thus has presented also a problem similar to the method of lowering the voltage applied to the variator-lens driving DC motor.
SUMMARY OF THE INVENTION
This invention is directed to the solution of the problems described in the foregoing. It is a first object of this invention to provide a video camera which is capable of zooming its lens without defocusing.
It is a second object of this invention to provide a video camera which is capable of zooming its lens without defocusing even in zooming at a high speed.
It is a third object of the invention to provide a video camera which is capable of zooming its lens without defocusing the lens even during the process of high-speed zooming from a wide-angle end position of the lens to a telephoto end position of the lens.
To attain these objects, a video camera which is arranged as a preferred embodiment of this invention to carry out a magnifying power varying action on a zoom lens while keeping a variator lens and a focus lens thereof in a predetermined relation comprises storing means for storing information on driving speeds at which the variator lens is to be driven at respective moving positions thereof and for storing information on a driving speed at which the variator lens is to be driven so as to make the focus lens driven at a predetermined constant speed in the neighborhood of a telephoto end position of the zoom lens, position detecting means for detecting et position of the variator lens and that of the focus lens, and control means for driving the variator lens and the focus lens, on the basis of information on a driving speed of the variator lens read out from the storing means according to a result of detection made by the position detecting means, in such a manner that a driving speed of the focus lens remains nearly constant in the neighborhood of the telephoto end position of the zoom lens.
It is a fourth object of this invention to provide a video camera which is capable of stably carrying out zooming and focusing even on the side of a telephoto end position of a zoom lens where a driving speed of a focus lens comes to increase.
To attain this object, a video camera which is arranged as a preferred embodiment of this invention to carry out a magnifying power varying action on a zoom lens while keeping a variator lens and a focus lens thereof in a predetermined relation comprises storing means for storing information on driving speeds at which the focus lens is to be driven at respective moving positions thereof, position detecting means for detecting a position of the variator lens and that of the focus lens, and control means for driving the variator lens and the focus lens, on the basis of information on a driving speed of the focus lens read out from the storing means according to a result of detection made by the position detecting means, in such a manner that a driving speed of the focus lens remains nearly constant in the neighborhood of a telephoto end position of the zoom lens.
A video camera arranged as another preferred embodiment of this invention to carry out a magnifying power varying action on a zoom lens while keeping a variator lens and a focus lens thereof in a predetermined relation comprises storing means for storing information on driving speeds at which the variator lens is to be driven at respective moving positions thereof and information on driving speeds at which the focus lens is to be driven at respective moving positions thereof, position detecting means for detecting a position of the variator lens and that of the focus lens, and control means for driving the variator lens and the focus le

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