Television cameras

Claim 2

A television camera including a camera tube of the kind having an optical image receiving photo-conductive target of selected area upon which an image is received covering an image area smaller than and having its edges lying inside the edges of said selected area which is scanned by a cathode ray over a raster area smaller than and having its edges lying inside the edges of said image area to develop picture signals over a video output area smaller than and having its edges lying inside the edges of said raster area, said camera also including electron gun cathode means for producing a cathode ray spot, means for causing said cathode ray spot to scan said raster area at television line and field frequencies, means for normally applying a selected voltage difference between said target and said electron gun cathode means during said scanning, and means for increasing said voltage difference during that part of field deflection in which the cathode ray spot is above the top edge of the video output area and below the bottom edge of the video output area.

Claim 3

A camera as claimed in claim 1 wherein means are also provided for increasing said applied target/electron gun cathode voltage during that part of line deflection in which the cathode ray is to the left of the left hand edge of the video output area and to the right of the right hand edge of the video output area.

Claim 4

A camera as claimed in claim 2 wherein said means for increasing the said voltage during field deflection includes an electronic switch device which is operative to change the potential applied to the electron gun cathode and is controlled by a control signal derived from the normally provided field deflection circuit of the tube.

Claim 5

A camera as claimed in claim 3 wherein said means for increasing the said voltage during line deflection includes an electronic switch device which is operative to change the potential applied to the electron gun cathode and is controlled by a control signal derived from the normally provided line deflection of the tube.

Claim 6

A camera as claimed in claim 4 wherein said means for increasing said voltage comprises a single electronic switch device, controlled by control signals derived from the normally provided field and line deflection circuits of the tube.

Claim 7

A camera as claimed in claim 5 including means for adjusting the value the target/electron gun cathode voltage.

Claim 8

A camera as claimed in claim 6 wherein said electronic switch device comprises three transistors in series across a D.C. potential source, the more positive two of said transistors being of opposite conductivity types and having their collectors connected together; means for applying to the bases of said two transistors a train of pulses derived from a deflection circuit of the tube to render the more positive of said two transistors conductive during fly back of the deflection in question, the said two transistors being alternately conductive; a fourth transistor; means for applying to the base of the fourth transistor a train of pulses also derived from said deflection circuit to render said fourth transistor conductive during periods slightly overlapping said fly back periods; means for applying voltaGe at the common collector junction of said two transistors to the electron gun cathode of the tube; and a circuit, completed when the fourth transistor is rendered conductive, for earthing the base of the least positive of the three series transistors.

Claim 9

In a television camera of the type having photo-conductive target means encompassing a selected area and within which selected area an image is received in an image area smaller than and having its edges lying inside the edges of said selected area, electron gun cathode means for producing a cathode ray spot, means for causing said cathode ray spot to scan said image area at television line and field frequencies to cover a raster area smaller than and having its edges lying inside the edges of said image area and within which raster area there is provided a video output area smaller than and having its edges lying inside the edges of said raster area, and means for normally applying a selected voltage difference between said target means and said cathode means during said scanning, the improvement comprising: control means connected to said means for causing scanning and to said means for normally applying voltage difference for causing an increase in said voltage difference when said spot is scanning at least within those boundary regions of said raster area above and below said video output area.

Claim 10

In a television camera of the type having photo-conductive target means encompassing a selected area and within which selected area an image is received in an image area smaller than and having its edges lying inside the edges of said selected area, electron gun cathode means for producing a cathode ray spot, means for causing said cathode ray spot to scan said image area at television line and field frequencies to cover a raster area smaller than and having its edges lying inside the edges of said image area and within which raster area there is provided a video output area smaller than and having its edges lying inside the edges of said raster area, and means for normally applying a selected voltage difference between said target means and said cathode means during said scanning, the improvement comprising: control means connected to said means for causing scanning and to said means for normally applying voltage difference for causing an increase in said voltage difference when said spot is scanning at least within those boundary regions of said raster area above and below said video output area.

Claim 11

In a television camera as defined in claim 8 wherein the last means causes said increase in voltage difference outside said video output area both in the television field and line directions.