This invention generally relates to instrument, such as camera, supporting tripods and more particularly concerns adjustable length tripod legs.
A desired attribute of a tripod is obviously rigid stability, but in a sense not always fully appreciated. Resistance to horizontal linear movement at the tripod head is less critical than is resistance to torsional, i.e., rotational, deflection of the tripod head. This is because a camera panhead typically imposes drag on rotational panning movement of the camera. The drag force tends to rotate the tripod head, and if the tripod deflects under this loading, when the camera is stopped and the loading released, the deflection will unwind and the camera will be turned in the direction opposite to that in which it was being panned. Particularly with long focus lenses, even slight movement of this kind will be readily apparent in the continuing image taken by the camera.
It will be apparent that the legs of a tripod for supporting an instrument should be longitudinally rigid when set at a desired adjustable length. For some uses, such as firmly supporting a movie or TV camera, it is desirable to control the leg length adjustment quickly so as to be able to set up the camera rapidly for operation. Still more rapid setup can be accomplished if the camera can be left secured to the tripod head and the tripod leg adjustment made while the camera is under the operator's physical control.
Accordingly, it is an object of the present invention to provide a tripod with adjustable length legs whose leg length adjustment can be made while operator is gripping and controlling the tripod head with an attached instrument.
It is a related object to provide a tripod of the foregoing kind which combines free sliding movement of a portion of the tripod legs for close incremental adjustment through the adjustment range together with rigid positive locking at the adjusted length.
A further object is to provide a tripod of the above type which maintains rigidity against torsional deflection about a vertical axis so that there is no backlash movement after a drag load has been imposed during panning.
Another object is to provide a tripod as characterized above that is economical to manufacture and trouble-free to use.