Patent GB-953867-A (GB)
Title: Improvements in or relating to camera arrangements, for example for television
Inventor: COOK GORDON HENRY
IPC: G02B15/14
Filed: 1960-01-14
Abstract: 953,867. Camera arrangements; variable focal length objective; wide angle attachments. RANK PRECISION INDUSTRIES Ltd., [trading as TAYLOR. TAYLOR & HOBSON]. July 13, 1960 [July 14, 1959; Jan. 14, 1960], Nos. 1412/60 and 23447/60. Divided out of 953,863. Heading G2J. A camera arrangement, for example for television, comprises a casing, an image-receiving unit having an image -receiving area of generally rectangular shape, an optical objective of variable equivalent focal length, the minimum value F 0  of which is not greater than 4 times the length of, the diagonal of the image-receiving area, and having front and rear assemblies, of which the front assembly includes members relatively movable for effecting variation of the equivalent focal length of the objective whilst maintaining the resultant image position constant throughout the range of relative movement, whilst the rear assembly has an inverted telephoto characteristic with effective axial beam diameter greater at its rear surface than at its front surface and includes a stationary convergent rear member having equivalent focal length f r  and in front thereof at least one member which co-operates with the front assembly to form a divergent group whose equivalent focal length bears to the equivalent focal length of the complete objective a constant ratio lying between f r /F 0  and f r /3F 0 , such divergent group acting to produce a virtual image of the object in a constant position lying between f r  and 4f r  in front of the front surface of the said convergent rear member, whereby such rear member always receives a divergent beam and forms from such virtual image a resultant image of the object at a back focal distance behind the rear surface of the convergent rear member greater than 6 times the length of the diagonal of the image-receiving area, means for mounting the image-receiving unit and the optical objective side by side within the camera casing with the image-receiving area at the rear end of the image-receiving unit, and means for deflecting the image-forming beam emergent from the rear surface of the objective to cause it to be incident on the image-receiving area at an effective distance from the rear surface of the objective equal to the back focal distance of the objective. As shown in Fig. 4, a television camera enclosed in a casing B incorporates a zoom lens A and on the side thereof a signal generating tube C with image-receiving area C<SP>1</SP> disposed in the image plane of the zoom lens and to which light is transmitted from the zoom lens after reflection at D and D' and passage through a filter turret D<SP>2</SP>. In another form the television camera is for colour operation and includes in addition to the zoom lens A three signal generating tubes G', G<SP>2</SP> and G<SP>3</SP> with image receiving areas G<SP>4</SP>,G<SP>5</SP> and G<SP>6</SP> to which light of a particular colour is transmitted from the zoom lens by partially transmitting and colour selective reflectors at H and H<SP>3</SP>, Fig. 7. In addition to the zoom lens and the signal generating tubes, the cameras each include a unit containing the electrical equipment and a viewfinder which may be an electronic viewfinder. The camera may alternatively be a kinematograph camera, Fig. 8, having zoom lens A and from which light is directed by reflectors D, D<SP>1</SP> to a film passing through a gate J to which it is fed between spools K and K<SP>1</SP> by a transport mechanism. The zoom lens A may be as disclosed in Specifications 953,863 and may also incorporate the inventions disclosed in Specifications 953,864 and 953,865. Optical data is given in this Specification for three examples of such objectives in one of which the front assembly consists of two movable members whereas in the other two examples the front assembly has four movable members and is of afocal. In each case the rear assembly incorporates a divergent middle member which is movable to two preset positions so that two ranges of variation of the equivalent focal length of the complete objective can be obtained. In addition to having a zooming movement the front member of the objectives may be movable for focusing. For close-ups however, it is desirable to use the invention disclosed in Specification 953,866 which is a substantially afocal wide angle attachment. This attachment may be mounted on rails on the front of the camera casing so that they may be removed at will from an inoperative position into an operative position directly in front of the objective. Such attachment when provided thus gives four ranges of variation of equivalent focal length. The attachment preferably comprises a divergent compound component axially spaced in front of a convergent compound component optical data being given in the Specification for two examples of an attachment as shown in Fig. 11.