c. With the focal length given a fixed camera to object distance, short
focal length lenses or wide angle zoom positions have a great depth of
field.
Long or telephoto lenses or narrow angle zoom positions have a
shallow depth of field.
Large aperture openings (small f-stop numbers)
cause a shallow depth of field.
Small lens opening (large f-stop number)
provides a great depth of field.
Learning Event 2:
DESCRIBE HOW TO OPERATE A ZOOM LENS
1.
There are two basic controls needed to operate a zoom lens: the zoom
control unit which activates the variable focal length of the lens (the
zooming mechanism) and the focus control unit which activates the intricate
focus mechanism in a zoom lens. Both controls can be operated manually or
automatically by a servo control.
a. On the ENG/EFP zoom lens, the manual control is a small rod extended
from the zoom ring for control of the zooming process. To zoom in or out
you would turn the zoom either clockwise or counter clockwise.
It takes
some skill and practice to accomplish smooth zooms with such a manual
control.
(1) The servo zoom control unit does not activate the zoom lens
mechanism directly, rather it signals a complex motor system that in turn
drives the zoom mechanism in the lens. The servo control can make a fast
zoom or slow zoom depending on the amount of pressure applied to the servo
rocker button.
(2) There are several advantages to the servo system.
Zooms are
steady and smooth, especially during slow zooms. The zoom control is easy
to operate and allows you to concentrate more on picture composition and
focusing. The servo zoom frees your left hand to operate the manual focus
and aperture controls.
b. The focus control is a manual function.
To operate this control,
the operator would rotate the focus ring on the zoom lens, either counter-
clockwise or clockwise, while looking into the viewfinder to determine if
the picture is sharp and in focus.
Some cameras come with an automatic
focus device that works on a simple radar principle. The camera sends out
an infrared beam that is bounced back to the camera by objects to be
photographed. The camera then computes the distance and adjusts the focus
accordingly.
Obvious problems occur when you want to focus not on the
object that lies next to the camera, but on the one farther away.
c. The zoom lens is used to mount other controls such as the Automatic
Iris Control, the VR remote control button, and the manual iris control.
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