c. Contrary to the fixed focal length lenses, the zoom lens can assume
all focal lengths from the wide angle position to the narrow angle position.
This is why it is called the variable focal length lens.
You can change
from a wide angle to a narrow angle with one continuous operation, without
changing lenses or moving the camera. The zoom in means to change the vista
gradually from a wide angle view to a narrow angle view. On television the
zoom seems to appear as if the object is coming towards you. When the lens
zooms out, the object is getting smaller and seems to move away from you,
but the camera remains stationary during the operation.
(1) A picture is in focus when the projected image is sharp and
clear.
The focus depends on the distance from lens to the pickup tube.
Simply changing the distance from the lens to the pickup tube brings the
image into or out of focus.
(2) A zoom lens has several lenses that move in relation to one
another when you zoom as well as when you focus. One set of these sliding
elements, normally located at the front part of the lens, takes care of
focusing.
(3) The focus control on the ENG/EFP has a focus ring that you must
turn by hand on the lens. If properly preset, a zoom lens keeps in focus
during the entire range, assuming that neither the camera nor the object
moves very much.
(4) Sometimes the operator has to "follow focus" and operate the
focus control while at the same time zooming in on the object. To preset
the zoom for focusing during a zooming operation so that the camera stays in
focus throughout the zoom, the operator must first zoom all the way in on
the object and get the sharpest focus and then zoom out to a long shot or
the desired shot. When the operator starts to zoom back to the long shot,
he will see that everything stays in focus.
2.
The lens aperture on a television camera is like that of the human
eye.
All lenses have a mechanism to control the amount of light that is
admitted through the lens. This mechanism is called the diaphragm or iris.
a. The iris consists of a series of thin metal blades that form a
fairly round hole. If you set the lens to its maximum aperture, it admits a
maximum amount of light.
If you close the lens, the metal blades of the
diaphragm forms a smaller hole. The aperture is then smaller and less light
goes through the lens. If you close the lens to its minimum aperture, very
little light goes through.
Some diaphragms can be closed entirely, which
means no light is permitted to enter.
b. The standard scale that indicates how much light goes through a
lens, regardless of whether it is a wide angle or telephoto lens, or any
other type of zoom lens is the f-stop. The lower f-stop (f/1.2) indicates a
relatively
35
Previous Page
