Figure 8-10.--Structure of the vidicon tube.

The image orthicon may be used for indoor or

dark. When an image is formed on the target by the

outdoor TV pickups. With this tube, scenes may be

camera lens, each element becomes conductive in

proportion to the amount of light falling upon it.

televised under light levels as low as 3 foot-candles

illumination (ordinary room lighting). However, light

Electrons flowing from the lowered resistance of the

levels of approximately 30 foot-candles provide

illuminated elements leave an electrical pattern on the

scanning side of the photoconductive layer. The

broadcast quality results. This is important in some

Navy applications.

electrical pattern formed corresponds to the light areas

of the optical image. The time required for the pattern

Vidicon

to form is less than the time of one television frame.

As the electron beam scans the electrical pattern

The vidicon is a small television camera pickup

of the optical scene, electrons flow to the elements

tube. Its relative simplicity and small size permit its

having the most positive charges. The small current

use in television cameras of very compact design. All

generated in each element flows through the

vidicons are similar, differing primarily in specific

transparent conducting film, the signal electrode, and

size, sensitivity, and resolution.

the load resistor to develop the video output signal.

When the beam scans a dark area, each element in the

The target area of the vidicon tube is made up of

two layers. The outer layer is a transparent conducting

dark area becomes negatively charged. When this

film on the inner surface of the glass faceplate. The

occurs, most of the beam is turned back. When the

entire surface is dark, a very small current flows to the

inner layer is a photoconductive material on the

load resistor and is called the dark current.

scanning side of the signal electrode. This is illustrated

in figure 8-10. The low-velocity beam is focused at the

Vidicons should always be handled and shipped

target surface by the combined effects of the

face up. Turning the tube face down could cause loose

electromagnetic focus coil and the electrostatic focus

particles within the tube to spot the surface.

field. A fine mesh screen is located near the

photoconductive layer. This screen forms a uniform

TYPES OF LENSES

decelerating field with the photoconductive layer,

which the beam passes through. This field causes the

The desired type of image or the size of camera

beam to land perpendicular upon the surface of the

coverage requires different types of lenses. The size

target. The electron beam is made to scan the

of the lens (fig. 8-9) varies from small and short to

photoconductive layer by the vertical and horizontal

large and long. The purpose of the various lenses

deflection coils.

varies from the wide-angle lens for large area coverage

to the telephoto lens for narrow coverage at long

Each small element of the photoconductive

distances.

material acts as an insulator when the element is in the

Figure 8-10.--Structure of the vidicon tube.

8-13