Chapter 3 The Video Camera and Support Equipment
61
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Focus ring
Zoom ring
F-stop ring
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Figure 3-16. A
professional lens has at
least three movable rings:
the focus ring, the zoom
ring, and the f-stop ring.
The “back” of the lens is the end of the lens assembly that attaches to the
camera. The “front” of the lens assembly is the part closest to the subject
being photographed or fi lmed. Camera lenses are classifi ed by the focal
length measurement. Since the optical center of a zoom lens can vary its
position within the lens assembly, the focal length measurement varies as
well. Therefore, a zoom lens is also called a variable focal length lens.
Controlling Light
There are at least three movable rings on a professional camera lens
assembly, Figure 3-16:
• The focusing ring is furthest away from the camera body. This ring
adjusts the focus of the image in the frame of the picture.
• The zoom ring is in the middle of the lens assembly and moves the
zoom lens forward and backward.
• The f-stop ring is the ring nearest to the camera. This ring is an
external indicator of the amount of light passing through the lens and
reaching the CCD. The f-stop ring regulates the amount of light that
passes through the lens by controlling the iris and, therefore, the size
of the aperture.
variable focal length lens:
A camera lens in which
the optical center can vary
its position within the lens
assembly, varying the focal
length measurement as well.
Also called a zoom lens.
When you enter a dark movie theater, your eyes dilate. The
part of your eye that determines eye color, the iris, contracts.
When the iris contracts, the pupil gets larger. The pupil is the
black part in the center of the eye that is essentially a hole that lets light
into the eye. With the pupil enlarged, more light can enter the eye to reach
the rods and cones of the retina. This allows you to see in a darkened
Visualize This
Three specifi c components of a lens assembly work together in regu-
lating the light: aperture, f-stops, and iris.