EP0540093B1 - Image tube with electrostatic shutter and imaging device - Google Patents

Description

• une source d'électrons émettant un flux d'électrons en réponse à une image photonique incidente, le flux d'électrons se propageant dans le tube-image à travers un réseau d'équipotentielles,
• des moyens de focalisation et d'accélération desdits électrons,
• des moyens d'obturation situés entre la source d'électrons et les moyens de focalisation et d'accélération pour interrompre le flux d'électrons, les moyens d'obturation comprenant une électrode d'obturation de type annulaire qui possède une ouverture centrale E à travers laquelle transite le flux d'électrons,
• une cible sur laquelle le flux d'électrons inscrit une image finale.

The invention relates to an electrostatic shutter picture tube comprising:

• a source of electrons emitting a flow of electrons in response to an incident photonic image, the flow of electrons propagating in the image tube through a network of equipotentials,
• means for focusing and accelerating said electrons,
• shutter means located between the electron source and the focusing and accelerating means for interrupting the flow of electrons, the shutter means comprising an annular type shutter electrode which has a central opening E to through which the electron flow transits,
• a target on which the flow of electrons registers a final image.

It also relates to a shooting device provided with such a picture tube.

In the field of image shooting, it is generally necessary to be able to interrupt or establish shooting for a very short period of time. Either it depends on the creation of a rapidly evolving series of images, or the target requires such functioning.

US Patent 4,528,447 is known which describes an electrostatic obturator tube provided with pairs of orthogonal deflection plates. A shutter electrode G1 is produced in the form of a cylinder provided with a grid. It is placed between a photocathode and a focusing electrode G2. The photocathode, which receives the incident image to be detected, has a curved surface. The cylindrical sealing electrode G1 has a length substantially equal to its radius. Facing the photocathode, thin, evenly spaced metallic wires conform to the shape of a spherical cap practically identical to that formed by the concave photocathode. Such a grid constitutes a production difficulty.

When operating as an "open" shutter, the electric fields E ₁ and E ₂ on either side of the slots defined by the inter-wire spaces must be equal so as not to create unidirectional microlenses which would seriously affect the quality of the final image. It is the adjustment of the potential V _G1 of the electrode G1 which makes it possible to satisfy the condition E ₁ = E ₂ because in practice the potential V _G2 of the electrode G2 is imposed by the focusing conditions. The potential of G1, which is positive with respect to the photocathode in open operation, becomes slightly negative in order to repress the photoelectrons emitted with a certain initial speed in closed operation. In this shutter function, the G2 electrode does not intervene because it is far from the photocathode and is strongly shielded by the relatively bulky G1 electrode, so that it is not necessary to modulate the potential of G2 to improve shutter sensitivity.

In addition, the presence of grid wires can raise a problem of making the photocathode when it is made "in situ". Indeed, the grid constitutes a light mask with respect to the evaporation of the constituents Sn, Cs, K intended to form the photocathode. Furthermore, these wires can be the site of parasitic emissions during operation of the tube.

Patent FR-A-2,082,509 is also known, which describes a cinematographic recording tube for one-dimensional images. It concerns a slit camera in which the photocathode occupies only a very small part of the internal face of the entry window. The illumination of this photocathode is limited to a slit, the purpose of this camera being to analyze the brightness of the line which forms on the target after focusing of the electron beam.

This tube has a switching electrode placed midway between the photocathode and a focusing electrode. The configuration of the electrodes is provided for processing a one-dimensional image. The aim of this camera not being to process two-dimensional images, it is obvious that the characteristics of this switching electrode, as revealed by this document, do not ensure good spatial resolution and good linearity ( negligible image distortion) in the case of a two-dimensional image. The modulation sensitivity of the switching electrode is also not suitable.

Furthermore, this switching electrode constitutes a sort of shielding of the focusing electrode, which prohibits associating the switching electrode and the focusing electrode to increase the modulation sensitivity.

The object of the invention is to overcome these difficulties in order to define a picture tube with electrostatic shutter which is easier to industrialize and which makes it possible to use instantaneous currents for controlling the shutter which are weaker and therefore easier to control. This object is achieved with an image tube provided with an electrode having, around the central opening E, a border of a small thickness and a shape substantially merging with part of one of said equipotential so that in transmission the shutter electrode does not disturb by its presence the network of equipotentials which would exist in the absence of such a shutter electrode.

By the word "border", it is necessary to understand a part, close to the center of the electrode, which can represent half of the electrode, the external part, close to the envelope of the tube, being determined by mechanical imperatives of fixing and electrical for electrical isolation.

The shutter electrode is given the form that the equipotential would have in the absence of an electrode shutter. Its thickness must therefore be very small. In this way, the transmission of the electron flow is not altered. The electrons pass through the central opening which is not obstructed by a network of metallic wires.

The shape of the electrode must be very careful. Indeed, it is not a question of transmitting a thin electron beam but the whole of a two-dimensional image. It is therefore not acceptable for degradations in the form of distortions to appear in particular on the contours of the image. Ideally, the electrode should have almost zero thickness. This is not possible in practice, a compromise consists in giving it a very small thickness (for example less than substantially 0.2 mm) on the edge of the central opening by accepting a progressively greater thickness as it approaches the periphery of the tube.

It is the face of the electrode which faces the focusing means which must be the most rigorously determined. This face must, in fact, be well parallel to the equipotential on which the shutter electrode is superimposed. Thus, the equipotentials which adjoin on either side the shutter electrode are not modified compared to the situation of an identical tube which would be devoid of shutter electrode. For this, the shutter electrode is defined so that said border is placed in an area where the equipotentials form monotonic curves substantially parallel to one another.

The shutter sensitivity can be defined as the ability of the tube to shut off the flow of electrons by a low control potential. To increase the shutter sensitivity of the electrode, the diameter of the central opening can be reduced. This is determined according to the size of the electron source, preferably a photocathode. The diameter of the central opening and the diameter of the photocathode are preferably included in a ratio ranging substantially from 1 to 2 approximately. Similarly, the shutter sensitivity can be modified by adjusting the distance between the shutter electrode and the photocathode. Preferably, the distance between the center of the central opening and the center of the photocathode is substantially equal to a quarter of the diameter of the central opening.

Thus, by its shape and its location, the shutter electrode does not constitute a shielding between the focusing electrode and the photocathode.

It is also possible to control the shutter by acting simultaneously on the shutter electrode and on the focusing means.

• figure 1 : un schéma d'un tube de prise de vues formé d'un tube-image ne possédant pas d'électrode d'obturation et ayant une cible constituée d'un dispositif à transfert de charges (DTC),
• figure 2 : une représentation des lignes équipotentielles et des trajectoires électroniques dans le tube de la figure 1,
• figure 3 : un tube de prise de vues avec une électrode d'obturation,
• figure 4 : une représentation semblable à celle de la figure 2 avec l'électrode d'obturation se superposant à l'équipotentielle 90 volts (mode de transmission de l'image électronique),
• figure 5 : une représentation semblable à celle de la figure 4 en mode d'obturation,
• figure 6 : un schéma électrique des potentiels appliqués au tube,
• figure 7 : un schéma partiel d'un tube-image avec une électrode d'obturation et une électrode de focalisation modifiée,
• figure 8 : un schéma de la partie du tube de prise de vue avec une cible formée d'un écran luminescent, de fibres optiques et d'un dispositif à transfert de charges,
• figure 9 : un schéma d'une partie d'un tube-image avec en plus des moyens de déflexion,
• figure 10 : une représentation d'une séquence d'images sur l'écran.

The invention will be better understood using the following figures given by way of non-limiting examples which represent:

• FIG. 1: a diagram of a picture-taking tube formed by an image tube having no shutter electrode and having a target made up of a charge transfer device (DTC),
• FIG. 2: a representation of the equipotential lines and of the electronic trajectories in the tube of FIG. 1,
• FIG. 3: a picture tube with a shutter electrode,
• FIG. 4: a representation similar to that of FIG. 2 with the shutter electrode superimposed on the 90 volt equipotential (transmission mode of the electronic image),
• FIG. 5: a representation similar to that of FIG. 4 in shutter mode,
• FIG. 6: an electrical diagram of the potentials applied to the tube,
• FIG. 7: a partial diagram of a picture tube with a shutter electrode and a modified focusing electrode,
• FIG. 8: a diagram of the part of the shooting tube with a target formed by a luminescent screen, optical fibers and a charge transfer device,
• FIG. 9: a diagram of part of an image tube with, in addition, deflection means,
• Figure 10: a representation of a sequence of images on the screen.

In the description, a "picture tube" is a tube which receives an incident image and renders a final image whatever the type of target. When the picture tube includes specific means which allow the final image to appear in the form of a video or other electrical signal, the picture tube then takes the name of picture tube.

• une enveloppe 11 qui peut être en verre,
• une photocathode 12 qui reçoit une image incidente et la transforme en un flux d'électrons,
• une électrode G2 13 qui focalise les électrons et qui se prolonge par une métallisation de l'enveloppe 11,
• une anode 16,
• une cible 14 constituée d'un dispositif à transfert de charges (DTC),
• des moyens 15 pour appliquer sur la cible et extraire de la cible des signaux électriques.

FIG. 1 schematically represents an example of a shooting tube 10 having an image tube comprising:

• an envelope 11 which may be made of glass,
• a photocathode 12 which receives an incident image and transforms it into a flow of electrons,
• an electrode G2 13 which focuses the electrons and which is extended by a metallization of the envelope 11,
• an anode 16,
• a target 14 consisting of a charge transfer device (DTC),
• means 15 for applying to the target and extracting electrical signals from the target.

According to a different embodiment, it may be an image tube for which the target consists of a luminescent screen, for example deposited on optical fibers. The means 15, transforming the picture tube into a shooting tube, then consist for example of a DTC coupled by optical fibers to said luminescent screen.

• potentiel de la photocathode 12 : 0 volt,
• potentiel de l'anode 16 et de la cible 14 : 14 000 volts,
• potentiel de l'électrode G2 13 (focalisation) : 365 volts.

FIG. 2 represents, for the tube of FIG. 1, the equipotential lines and the electronic trajectories of the electrons forming the final image with the following applied potentials:

• potential of the photocathode 12: 0 volts,
• potential of anode 16 and target 14: 14,000 volts,
• potential of electrode G2 13 (focusing): 365 volts.

The equipotential lines are spaced successively, from the photocathode towards the anode, by steps of 5 volts then 30 volts, then 100 volts, then 500 volts.

FIG. 3 is a diagram similar to that of FIG. 1 with a shutter electrode G1 17 interposed between the photocathode 12 and the focusing electrode G2 13.

FIG. 4 is a representation of the equipotential lines and of the electronic trajectories for the image pickup tube of FIG. 3. The shutter electrode 17 is here polarized at 90 volts to be superimposed on the 90 volt equipotential. Compared to FIG. 2, the electronic flow then remains unchanged. This annular sealing electrode is very external to the electron beam and therefore its concentricity is not critical. It is the border 27 (FIG. 3) around the central opening which is of great importance from the point of view of electronic optics: the thickness of the electrode G1 and its inclination relative to the axis of the tube. are important.

As regards the central part of this electrode G1 (FIG. 3), it is preferably constituted by a spherical segment of very small thickness (for example 0.1 mm) representing at best the shape of the equipotential previously calculated and represented on Figure 2. Insofar as it is expected that this electrode G1 is made in turn in one piece, the walls are preferably machined with a straight cross section (and slightly flared to ensure good rigidity). The most important angle is that of the wall facing G2: it is close to the average angle of the equipotential materialized in this area and, in all rigor, is optimized to find the results illustrated in Figure 4, which correspond to a minimum of defects of the final image (that is to say of non-linearity and loss of resolution on the edges), that is to say in perfect agreement with those of FIG. 2.

For the tube structure considered here, the measurement of this angle relative to the axis is 73 degrees and this value should be respected. Of course, a different structure could lead to a different angle.

The structure described defines an opening E of G1 of diameter 2 R _G1 = 32 mm for an emissive diameter 2 R _PK = 22.4 mm on the photocathode, ie a ratio 32 / 22.4 = 1.43 which characterizes in particular the quality of final image.

In the hypothesis of a less demanding on the quality of the edges of final image, one can increase the action of G1 by bringing the "point" of this electrode closer to the edge of the flow of electrons. We can, for example, reduce the opening of G1 to 26 mm (instead of 32 mm), which brings said ratio to 1.16 and thus allows reduce the amplitude of the electric shutter pulse.

A similar improvement in shutter sensitivity can be obtained, at roughly constant final image quality, by also reducing the emissive diameter in the same ratio, i.e. by bringing it to 18.2 mm (to find the ratio 1.43 = 26 / 18.2). Note that this is done by plating, outside the tube, on the support of the photocathode, a mask of dimensions appropriate to the use and thus delimiting the emissive surface.

In other words, the same tube can have a high shutter sensitivity and an average quality of the final image edges, or keep this sensitivity on a reduced final image with good qualities.

As for the thickness of the edge of this electrode G1 (in the vicinity of the edge of the electron beam), it can be increased to 0.2 mm without degrading the results. A greater thickness is only envisaged - for reasons of ease of machining - if the quality of the edges of the final image is the subject of less demanding.

The position of G1 should not be arbitrary. On the structure described, the distance DG1 between its "tip" and the plane tangent to the center of the photocathode is equal to 7 mm (and in this case, DG1 / 2R _G1 ≃ 0.22).

If we reduce this DG1 distance, the trajectory blocking sensitivity only improves a little for the edge of the electron beam but does not change at the center of it (around the axis). Furthermore, the parasitic capacitance C _p increases due to this proximity of G ₁ and the support of the photocathode. Finally, with too great a reduction in DG1, this electrode G1 leaves the zone where the equipotentials correspond by translation, which results in a mechanically critical solution, that is to say that the obturation electrode can no longer be properly compensated electrically.

If on the other hand G1 deviates too much from the photocathode, this latter drawback also appears, but in addition, the shutter sensitivity of the beam decreases.

FIG. 5 shows how the electron flux is shut off when this electrode G1 is negatively polarized (the focusing electrode G2 remaining at its nominal focusing value V _G2 = 365 volts). The 0 volt equipotential is closed on the axis, near the center of the photocathode, thus defining a cut-off. Between the photocathode and this 0 volt equipotential, the equipotentials are negative and the electric field is first repulsive in the vicinity of the photocathode. We also observe electronic trajectories emitted with a certain initial speed and turning back from the first calculation steps. To obtain this result, it is necessary to bring V _G1 to - 360 volts, which means that one passes from the "blocked" state to the "unlocked" state with a pulse of 90 - (- 360) = 450 volts.

   avec :

• C = capacité de G1 par rapport à l'ensemble de son environnement (capacité totale),
• dV = ¦V¦, amplitude du créneau,
• dt = t, temps d'obturation désiré, qui peut être de l'ordre de la nanoseconde.

The electrode G1, by its shape and its position in the tube, has a low electrical capacity compared to its environment. This has an advantage for the generation of shutter control pulses. These pulses must make it possible to deliver instantaneous currents which may be high. Current I can be expressed by $$\mathit{\text{I}}\text{=}\mathit{\text{VS}}\frac{\mathit{\text{dV}}}{\mathit{\text{dt}}}$$

with:

• C = capacity of G1 in relation to all of its environment (total capacity),
• dV = ¦V¦, amplitude of the slot,
• dt = t, desired shutter time, which can be of the order of a nanosecond.

The total capacity C is divided into:

C = C _o + C _p where C _o is the capacity of G1 in relation to the useful photocathode surface and where C _p , parasitic capacity, groups all the rest (capacity of G1 in relation to the focusing G2, to the accelerator , to the shielding of the tube ... and to the photocathode support).

Is : $$\mathit{\text{I}}\text{=}\frac{\mathit{\text{V}}}{\mathit{\text{t}}}\text{((}{\mathit{\text{VS}}}_{\mathit{\text{o}}}\text{+}{\mathit{\text{VS}}}_{\mathit{\text{p}}}\text{)}$$

En effet, lorsque G1 s'approche de la surface émissive, le flux du champ créé sur celle-ci augmente et il est évident que cela se traduit simultanément par une augmentation de C_o et de l'action sur le contrôle de l'émission.It is observed that the modulation sensitivity is proportional to C _o : $$\mathit{\text{V}}\text{=}\frac{\mathit{\text{k}}}{{\mathit{\text{VS}}}_{\mathit{\text{o}}}}$$

In fact, when G1 approaches the emissive surface, the flux of the field created on it increases and it is obvious that this results simultaneously in an increase in C _o and in the action on the control of the emission. .

Le rapport C_p/C_o doit être minimisé pour réduire la valeur instantanée du courant.The previous equation is then written: $$\mathit{\text{I}}\text{=}\frac{\mathit{\text{k}}}{\mathit{\text{t}}}\text{(1 +}\frac{{\mathit{\text{VS}}}_{\mathit{\text{p}}}}{{\mathit{\text{VS}}}_{\text{o}}}\text{)}$$

The ratio C _p / C _o must be minimized to reduce the instantaneous value of the current.

Furthermore, the shutter electrode has a total opening for the wide beam coming from the photocathode. Thus it does not constitute a shielding between the photocathode and the focusing electrode G2 so that it is possible to effectively combine shutter potentials applied simultaneously to the shutter electrode G1 and to the focusing electrode G2 .

$${\text{V}}_{\text{G2}}\text{= +60 + 305 = 365 volts.}$$

Figure 6 shows how to shut off the electron flow by associating a negative polarization of G1 and a reduction of the polarization of G2. It is obviously desirable to pass from the “blocked” state to the “unblocked” state using the same unblocking pulse applied to G1 and G2. Under these conditions, we observe that the cut-off is this time reached with V _G1 = - 215 volts and V _G2 = + 60 volts so that by superimposing on these polarizations the same brief pulse of 305 volts, we pass to l '' unlocked state which characterizes the nominal operation of the tube: $${\text{V}}_{\text{G1}}\text{= -215 + 305 = 90 volts}$$

$${\text{V}}_{\text{G2}}\text{= +60 + 305 = 365 volts.}$$

The polarizations are applied through resistors R ₁ and R ₂ respectively connected to the shutter electrode 17 and to the means 13. The pulse is applied using the capacitors C ₁ and C ₂ .

The indicated potentials relate to the case of a target formed of an electroluminescent screen, that is to say with an electron source brought to 0 volts and an anode brought to 14,000 volts. In the case where the target is a charge transfer device, the electron source is then brought to -14,000 volts and the anode is brought to 0 volts. We must then subtract 14,000 volts from the potentials in Figure 6.

Thus, the simultaneous use of G2 and of the annular electrode G1 makes it possible to gain approximately 50% on the sensitivity of modulation.

It is also possible to apply the concept of the invention to the focusing electrode G2 in order to increase its sensitivity. FIG. 7 shows that it is possible to provide the input of the focusing electrode G2 with a cylindrical flange 23 of small thickness conforming to the equipotential closing on the focusing electrode G2 in mode of transmission of the electronic flux.

The target of such an image tube can be formed either by an electroluminescent screen or by a charge transfer device sensitive to the flow of electrons. FIG. 8 is a schematic view of a part of a shooting tube in which the target 14 consists of a luminescent screen 14a coupled by an optical fiber 24 to a charge transfer device 14b. The electron flow is therefore transformed into photonic flow by the luminescent screen 14a. The photonic flux is then detected by the charge transfer device 14b.

The image tube can also contain means for electrostatic deflection 20 in the space adjacent to the target (FIG. 9). It is thus possible to intervene on the position of the final image on the target. For this we generate a final image occupying only part of the target. This is obtained either by construction of the tube or by masking the extent of the photocathode if the image reduction is not planned at the start. A series of reduced final images can represent a series of different final images taken consecutively by the shooting tube. It is then necessary to synchronize the shutter means and the deflection means using an image sequencer 21.

This structure is particularly interesting in the case of ultra-fast cinematography where it is then possible to examine a series of different consecutive final images 1, 2, 3 ... (Figure 10). One can thus trap in said suite an isolated event appearing in one of the final images by stopping the sequencer, or else follow the same event with high temporal resolution.

To examine the information contained in said sequence of final images "off-line", it is necessary to be able at a given instant to stop the acquisition of the final images. This is particularly the case when the target is formed of a DTC charge transfer device sensitive to the flow of electrons.

• soit par construction d'un DTC avec un petit nombre de pixels,
• soit, si la technologie du DTC le permet, par un fonctionnement où l'on regroupe plusieurs pixels adjacents en macropixels ou éventuellement en n'utilisant qu'une partie du DTC.

In conventional ultra-fast video imaging using a DTC, the acquisition of a sequence of images consists of a succession of recording (exposure) and reading cycles. The frame rate is a function of the time required for each of these cycles. In the current state of the art, the limitation comes from reading the shooting device. To increase the frame rate (F _T ), the reading time must be reduced by reducing the number of pixels to be used. This reduction in the number of pixels leads to a reduction in the spatial resolution of the DTC and therefore of the image recorded (expressed in number of pixels per image); it is obtained:

• either by building a DTC with a small number of pixels,
• or, if DTC technology allows, by an operation in which several adjacent pixels are grouped in macropixels or possibly by using only part of the DTC.

The increase in frame rate by a decrease in spatial resolution, in addition to being of limited benefit due to the loss of information, also has physical limitations. Indeed, the maximum bandwidth of the shooting device is limited by the maximum frequency of the video signal, that is to say by the time required to read a pixel. This time is determined by the DTC manufacturing technology.

By also accepting a reduction in spatial resolution, it is possible according to the invention to reduce the image itself, in order to be able to record, prior to the extraction of the data, a succession of these reduced images on the entire sensitive area of the DTC. Said series of reduced images is then obtained at an acquisition rate which is independent of the reading time of the DTC, a rate which can be very high provided that there is a rapid shutter between a reduced image and the following reduced image. in order to avoid dragging phenomena in the image, which are particularly harmful when the deflection time becomes commensurable with the exposure time.

To obtain very high rates, it is advantageous to limit the exposure time therefore to use a target with high detectivity. This can be achieved by bringing the flow of electrons to the back of an electron-sensitive DTC. To increase this detectivity to the maximum (until the detection of the single electron), it is possible to use a thinned DTC of the order of ten microns.

The non-dependence of said acquisition rate with the time for reading the data (therefore the number of pixels to be read), makes it possible to use DTCs of large dimensions having a large number of pixels. This makes it possible to obtain reduced images of good resolution.

By way of example, a shooting tube provided with the shutter electrode made it possible to achieve a shutter time of approximately 10 ns. Thus with a DTC of 1024 x 1024 pixels, and reduced final images of 64 x 64 pixels, it is possible to take a series of 256 reduced final images. With a shutter time of 10ns between two final images, during which the deflection means deflect the flow of electrons by 1 image step, and with an acquisition time of 40ns for a reduced final image, it is possible to record a series of final images for 50ns x 256 = 12.80 microseconds. This sequence can be extracted globally from the DTC later and then analyzed.

This method provides a considerable gain in speed compared to the method consisting in operating a data extraction after each reduced final image entered in the DTC.

Claims (11)

1. An electrostatic shutter image tube (10) comprising:

   - an electron source (12) emitting a flow of electrons in response to an incident photon image, the flow of electrons being propagated in the tube through a network of equipotential lines,

   - means (13) for focusing and accelerating said electrons,

   - shutter means (17) situated between the electron source and the focusing and accelerating means, for interrupting the electron flow, said shutter means comprising a ring-shaped shutter electrode 17 having a central aperture E for allowing passage of the flow of electrons,

   - a target (14) on which the electron flow inscribes a final image,

   characterized in that said shutter electrode (17) has a rim (27) of small thickness around the central aperture E and the shape of the rim is such that it substantially merges with a part of one of said equipotential lines in order that, during transmission, the shutter electrode (17) does not disturb the network of equipotential lines which would exist if such a shutter electrode was absent.
2. An image tube as claimed in Claim 1, characterized in that said rim (27) is situated in a zone where the equipotential lines form monotonic curves extending substantially parallel to each other.
3. An image tube as claimed in Claim 1 or 2, characterized in that the ratio of the diameter of the central aperture to the diameter of the electron source ranges approximately between 1 and 2.
4. An image tube as claimed in one of the Claims 1 to 3, characterized in that the distance between the centre of the central aperture and the centre of the electron source is equal to approximately a quarter of the diameter of the central aperture.
5. An image tube as claimed in one of the Claims 1 to 4, characterized in that the thickness of the shutter electrode at the rim of the central aperture is less than approximately 0.2 mm.
6. An image tube as claimed in one of the Claims 1 to 5, characterized in that the electron flow is shuttered by simultaneously controlling the shutter electrode and the focusing means.
7. An image tube as claimed in one of the Claims 1 to 6, characterized in that the focusing electrode is provided, on the side of the electron source, with a cylindrical flange (23) the shape of which corresponds to an equipotential line which links-up with the focusing means (13) in the transmission mode of the electron flow.
8. A pick-up tube characterized in that it comprises an image tube as claimed in one of the Claims 1 to 7, the target (14) consisting of a charge transfer device.
9. A pick-up tube characterized in that it comprises an image tube as claimed in one of the Claims 1 to 7, the target (14) consisting of a luminescent screen (14a) which is coupled to a charge transfer device (14b) by optical fibres (24).
10. A pick-up tube as claimed in one of the Claims 8 or 9, characterized in that it comprises deflection means (20) for influencing the position of the final image on the target.
11. A pick-up means characterized in that it comprises a pick-up tube as claimed in Claim 10 and an image sequencer (21) which controls the deflection means (20) for influencing the position of a sequence of final images on the target (14).

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