GB2060918A - Measuring the focal distance from a cine camera - Google Patents

Abstract

The distance between a cine camera and the subject being photographed is measured after picture taking, in order to check focusing, by means of a sonic transducer (emitting sonic pulses at regular intervals and receiving the echoes from the subject) having a digital readout of the distance of the subject from the camera. The cine camera has an objective lens 13 with focusing ring 14 and lens shade member 17. A sonic transducer assembly 21, connected below member 17, is adjustable about a horizontal pivot 26 together with an auxiliary lens 34 which is connected to an eye piece 37 via a flexible fibre optics device 36. Assembly 21 is connected to a digital readout device in a housing 38 having a digital readout window 39, housing 38 being connected to the side member 17. The digital readout is adjustable to take into account the distance of assembly 21 from the film plane. <IMAGE>

Description

SPECIFICATION Sonic device for measuring focal distance for motion picture camera This invention relates to motion picture cameras and is particularly directed to an improved sonic pulse device for measuring the distance from the camera to a subject to be photographed and to provide a visual digital display of that distance.

In the use of professional motion picture cameras, a scene may be photographed a number of times in order to obtain the most satisfactory "take". If, for example, the scene requires an actor to move to a position near the camera and then to remain in that close position while delivering his lines, present practice makes it necessary to use a measuring tape after each "take" to be sure that his face remained in focus. Accordingly, there is required a tiresome repetition of manually measuring the distance from the camera to the actor each time a "take" is made.

According to the present invention there is provided, for use with a motion picture camera, a device for measuring the distance from the camera to a subject being photographed, the device comprising sonic transducer means adapted to be movably mounted on the camera at a location offset from the axis of the camera lens, said transducer means being adapted to emit sonic pulses at intervals toward a subject in the field of view of the camera lens and to receive echos from said subject, means for measuring the time difference between sending of a sonic pulse and receiving an echo from the subject, and means actuated by said measuring means for furnishing a digital display of the linear distance from the camera to the subject.

Thus the device of the present invention eliminates the need for repetitive use of the manual tape and instead provides a digital readout of the distance from the actor to the motion picture camera, the device employing a sonic pulse system.

Viewed more specifically, a feature of this sonic pulse system is a mounting for the sonic transducer which enables it to be moved with respect to a stationary support member, preferably a lçns shade of the camera, secured relative to the camera body. A small auxiliary lens is fixed with respect to the sonic transducer so as to move with it, and a viewing device, separate from the viewer for the main camera lens, is provided so that the camera operator may direct the sonic pulse to the face of the actor so that the echo received by the transducer provides a very accurate measurement. This measurement is converted by electronic circuitry to provide a digital readout in feet and inches, or in meters and centimeters.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a motion picture camera having a sonic pulse distance measuring device embodying this invention; Figure 2 is a perspective view showing principal parts of the sonic pulse distance measuring device including a flexible fiber optics viewer; Figure 3 is a sectional elevation taken substantially on the lines 3-3 as shown in Fig. 2; and Figure 4 is a sectional plan view taken substantially on the lines 4-4 as shown in Fig. 3.

Referring to the drawings, the motion picture camera generally designated 10 includes a camera body 11 and a through-the-lens viewer 1 2. The camera lens 13, removably secured to the camera body 11, is provided with a toothed ring 1 4 for adjusting the focus, and visual indicia 1 5 show the distance from the film plane to the subject being photographed. A plurality of removable support bars 1 6 support the lens shade member 1 7 which is of conventional form having a central opening aligned with the axis of the camera lens 13.

The motion picture camera 10 is provided with the usual film magazine 1 8 and is supported on a conventional head 1 9 for pan and tilt movements.

The lens shade 1 7 serves as a mount for the sonic transducer assembly generally designated 21. A bracket 22 is secured to the underside of the lens shade 1 7 and this bracket carries a plate 23 provided with spaced parallel vertical ears 24. The transducer assembly 21 is mounted on aligned horizontal pivot pins 26 carried by the bracket ears 24.

A coil compression spring 27 interposed between the transducer assembly 21 and a recess 28 in the plate 23 acts to swing the transducer assembly 21 in a counterclockwise direction as viewed in Fig. 3. An adjustable stop element 29 is mounted on one of the ears 24 and is provided with a rounded end 31 which engages an inclined surface 32 provided on the rear portion of the transducer assembly 21. From this description it will be understood that turning of the knob 33 turns the threaded element 29 to adjust the angularity of the transducer assembly 21 with respect to the lens shade 1 7.

A flexible fiber optics device 36 is fixed by means of bracket 35 to the lower portion of the transducer assembly 21. An auxiliary lens 34 is located directly below the principal axis of the main lens 1 3 and is fixed to the fiber optics device 36, so that the transducer assembly 21 and the auxiliary lens 34 move as a unit about the pivot pins 26. The camera operator uses the eye piece 37 to look through the small auxiliary lens 34.

The transducer assembly 21 is electrically connected to a power supply and to electronic circuitry contained within the housing 38 secured to the side surface of the lens shade 17. A window in the housing 38 provides a visual digital display 39 showing the distance from the film plane of the motion picture camera to the subject being photographed.

The distance from the front of the transducer assembly 21 to the camera film plane measured along the axis of the main lens 1 3 is taken into account in caiibrating the readout device 39. The transducer assembly 21 emits sonic pulses and receives the echo from the subject being photographed.

The transducer assembly 21 and the auxiliary lens 34 may be located at any desired position around the axis of the camera lens 13, the chief requiremenT being that the axis of the camera lens 1 3 and the axis of the auxiliary lens 34 remain in the same plane, and that the hinge axis around the pivot pins 26 be at right angles to that plane. Accordingly, the transducer assembly 21 and auxiliary lens 34 could be mounted at any desired position on the lens shade member 1 7 or other stationary support.

The following explanation relates to a typi cal use of the device of this invention. Assuming that an actor is required to walk toward the motion picture camera, stop, and deliver his lines, the main camera lens 1 3 is adjusted to bring cross hairs in the field of view into focus on the actor's face, or typically the cheek bone area thereof, when the actor is in the position to deliver his lines. A conventional manyal tape is then extended from the camera to the cheek bone area of the actor.

This measured distance, for example, six feet, should agree very closely with the indicia 1 5 on the main lens 1 3. The knob 33 is then turned to tilt the auxiliary lens 34 until the lens 34 is aimed directly at the position of the cross hairs on the cheek bone. The digital readout 39 is then adjusted to agree with the distance actually measured by the manual tape. These steps, of course, are taken during rehearsal, and before actual filming commences.

When the scene is photographed, the distance from the actor's face to the motion picture camera is shown on the digital readout device 39, and if this varies beyond acceptable limits, the "take" is out of focus and must be repeated. However, the tiresome repetitive use of a manual tape after each "take" is eliminated.

Claims (8)

1. For use with a motion picture camera, a device for measuring the distance from the camera to a subject being photographed, the device comprising sonic transducer means adapted to be movably mounted on the camera at a location offset from the axis of the camera lens, said transducer means being adapted to emit sonic pulses at intervals toward a subject in the field of view of the camera lens and to receive echos from said subject, means for measuring the time difference between sending of a sonic pulse and receiving an echo from the subject, and means actuated by said measuring means for furnishing a digital display of the linear distance from the camera to the subject.

2. A device as claimed in claim 1, further comprising a second lens associated with said transducer means and movable therewith relative to the camera, and means for viewing said subject through said second lens.

3. A device as claimed in claim 2, wherein said viewing means comprises a flexible fiber optics device.

4. A device as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

5. A motion picture camera having a camera lens mounted upon a camera body, means to focus the camera lens, a member secured relative to the camera body, and a device as claimed in any of claims 1 to 4 having its said sonic transducer means movably mounted on said member at a location offset from the axis of the camera lens.

6. A camera as claimed in claim 5, in which said member comprises a lens shade having a central opening aligned with the camera lens.

7. A camera as claimed in claim 5 or 6, when dependent directly or indirectly on claim 2, in which the axis of the camera lens and the axis of the second lens are located in the same plane.

8. A camera as claimed in claim 5, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.