Video camera tube

An image pickup tube is an electron tube that converts an optical image into electrical signals.

Camera tubes have been largely replaced by CCD sensors, in some areas, however, they are used as before.

Camera tubes can fundamentally only generate signals for monochrome images, color television, an upstream optics with color filters or a filter strip with corresponding electronic switching is necessary.

• 2.5.1 Plumbicon

Function

An image pickup tube consists of fundamentally

• A photocathode on the optical way to changing the image is projected,
• Of a scanning device which converts this exposure, electrostatic latent image equivalent to the photocathode in a discrete-time signal.

Types of camera tubes

The transformation described above, the optical image into a charge have all camera tubes together. The differences are found in the design details.

Iconoscope

The latent image is produced in this type over an array of small capacitor cells, which consist of light-sensitive material ( cesium ). Thus, this layer combines photocathode and storage of the charge image. This latent image is scanned line by line through an electron beam. The different charging of the capacitors results in a different current in the recharging of the capacitor cells and thus the electrical signal.

The Ikonoskop is by its mechanical design quite sensitive to the effects of secondary electron emission. The Rieselikonoskop compensated these parasitics by sprinkling the capacitor cell plate with separately generated electrons.

Superikonoskop

The Superikonoskop differs from the normal Iconoscope by separating the photocathode and storage layer. The photocathode is arranged here, the capacitor -cell layer, the charge- image thus generated is projected on the electron- optical storage layer. This increases the sensitivity by way of the gain ( acceleration) of the electron image by external fields.

Probe tube

Developed by Philo Farnsworth probe tube also generates again a charge image on a photocathode. About a suitable electron optics of this charge image is completely gone out line by line at the entrance of a secondary electron multiplier. There is already pre-amplified signal can be taken.

Orthicon

The orthicon has as the Ikonoskop a capacitor array of photosensitive material. This arrangement, however, is semi- transparent to light and is used by both sides. From the beginning, the optical image is projected to this arrangement, thus creating the charge image. From the back of an electron beam scans this image from charge in the manner known from Iconoscope.

In contrast to Iconoscope this electron is slowed down by appropriate measures at very low speeds, so that no secondary electrons are ejected from the photocathode. This electron beam is deflected again by the scanning of the capacitor cells and returns to the anode in the vicinity of the cathode. There, the signal can be removed.

Image - orthicon

This image pickup tube separates photocathode and the storage layer, similar to the Superikonoskop. In addition, between the photocathode and the storage layer, arranged close in front of the storage layer, a kind of grating which is intended to prevent the formation of secondary electrons.

A thin glass plate forms the rear side of the storage layer, the charge image is scanned by influence of time also by this plate by a slow and then reverse the deflected electron beam. Instead of a normal anode, the returning modulated electron beam is directed into a secondary electron multiplier.

In order for the image orthicon achieved compared with the Ikonoskop about four hundred times the sensitivity and thus can image recordings even in dull weather or normal lighting.

Vidicon

The translucent photocathode is the vidicon of semiconducting material whose resistance changes by exposure. Then sweeps the scanning electron beam, this semiconductor cathode as the current fluctuates due to the different conductivity of the more or less exposed areas.

The sensitivity of the vidicon is again a factor of 200 larger than those of image Orthicons.

Plumbicon

The plumbicon is used as a semiconductor layer of lead oxide, which offers certain advantages over materials used in the vidicon.

Other types

• The Isoskop, very common in the medical field,
• The graph echon works with two electron beams, a sample and a quenching jet, which spread a semiconducting layer from both sides,
• The Eriskop, a Iconoscope the related tube.

History

The Image Tube Camera ( image tube camera ) was the first camera that worked with an image pickup tube. It allowed exposure times of 1/2.000.000 second. The camera was developed at the Atomic Weapons Research Establishment in 1955 and first presented.