Matakuliah
Tahun
: O0382 – Dasar-dasar Produksi Siaran Televisi
: 2010
LENSES
Pertemuan 5
Types of Zoom Lenses (1/4)
The discussion will cover (1) studio and field lenses, (2) zoom range, and
(3) lens format.
Studio and field lenses
Studio lenses are normally used with studio cameras.
Field zooms included large lenses mounted on high-quality cameras used
for telecasts, such as sporting events. The field lenses are those on ENG/
EFP cameras and consumer camcorders.
Zoom range
Zoom range is the focal length of lens that can be changed during the
zoom. It is usually stated as ratio (such as 10:1 means the ability to
increase the shortest focal length up to ten times). The ratios vary
according to the type of the camera. The large studio cameras may have
zoom range of 40x to 70x, the smaller ENG/ EFP cameras rarely exceed
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15x zoom range.
Types of Zoom Lenses (2/4)
Optical and digital zoom range
An optical zoom range is 15x or 20x, or it may change the focal
length if the camera would like to reach the image enlargement in tighter
shot.
This would not happen in digital zooming where the electronics of
the camera simply select a center portion of the long shot and enlarge the
portion to screen size.
There is also interpolation, a process where a high-end consumer
cameras try to restore the full-pixel resolution of the original image. But
that gives quite different image quality from before-the-zoom image.
Studio, field, ENG/EFP lenses are all detachable from cameras.
Only consumer camcorders have built-in lens and cannot be detached.
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Types of Zoom Lenses (3/4)
Studio and large field lenses
In line with the function, the field lenses have much greater zoom
range (from 40x to 70x) and can deliver high-quality pictures than the
studio cameras.
ENG/ EFP lenses
These lenses have normal zoom range extends from 13x to 17x.
Or normally it would work in 15x zoom lenses for most of ENG/ EFP
activities.
Consumer camcorder lenses
Though consumer camcorder have zoom range of 10x to 18x the
maximum wide-angle position is often not wide enough. Most camcorders
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have some sort of image stabilization.
Types of Zoom Lenses (4/4)
Range extenders
Range extenders are optical elements that function as additional
lens elements enable the zoom lens to ‘reach’ the scene. Range
extenders are usually available on professional cameras. Range
extenders will shift magnification of the lens toward the narrow-angle end
of the zoom range. The disadvantages of using range extenders are: (1)
they cut down considerably the incoming light which will cause problem
especially in low-light conditions, (2) they may cause the picture to lose
some of its crispness.
Lens Format
Lens format refers to the standard NTSC cameras or HDTV
cameras and it is with the measurement of 1/3 inch, ½ inch, or 2/3 inch.
The use of lens corresponds with CCD image format; therefore, the larger
the CCDs the better pictures it produces.
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Optical Characteristics of Lenses (1/8)
Effective use of a camera depends on these optical characteristics: (1)
focal length, (2) focus, (3) light transmission – iris and f-stop, and (4)
depth of field.
Focal Length
Focal length is the distance from the optical center of the lens to the
camera’s imaging device (CCD imaging device) when camera is still.
When zoom out, the focal length of the lens is at the maximum wideangle position, the camera will provide a wide view, and the image will
reduce.
When zoom in, the focal length of the lens is at the minimum wide-angle
position, the camera will provide a narrow view (a close-up view), and the
image will enlarge.
The zoom lens could also perform variable-focal-length lens when the
zoom lens assumes all focal lengths from its maximum wide-angle
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position to maximum narrow-angle position.
Optical Characteristics of Lenses (2/8)
Minimum object distance and macro position
Minimum object distance (MOD) is the position where camera is
as close as it can get and still focus on the object. Most zoom lenses
have minimum object distance of 2 to 3 feet.
Macro position is the closest distance the camera can get to the
object without losing focus. In this position, the camera even almost can
touch the object and the zoom lens no longer in a variable-focal-length
but in a fixed-focal-length (‘prime’ lens). Macro position is usually applied
in very specific circumstances like taking close-up look of a postage
stamp.
The disadvantage of using macro position is before zooming
other object then the camera must switch back to normal zoom
mechanism upon completing that special assignment.
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Optical Characteristics of Lenses (3/8)
Focus
Focus means sharp and clear, and it depends on the distance
from the lens to the film or from the lens to the camera imaging device
(beam splitter with CCDs).
Presetting (calibrating) the zoom lens
Presetting (calibrating) zoom lens is conducted when automatic
focus control is absent from the camera.
Light transmission: iris and f-stop
Iris or lens diaphragm is a mechanism that controls how much
light is admitted through lenses. Iris consists of a series of thin metal
blades that form the aperture (lens opening) of variable size. The opening
size of the aperture will determine the amount of lights that come into the
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camera.
Optical Characteristics of Lenses (4/8)
As for f-stop, it is the incoming light measured from its scale. Most
camera types expressed the f-stop in a series of numbers such as f/1.7,
f/2.8, f/4, f/5.6, f/8, f/11 and f/16.
The f-stop number represent the iris opening and the amount of
incoming light. The smaller the number, the larger the iris opening and the
bigger mount of incoming light into camera. It is because the f-stop
numbers express ratio. For example f-stop f/4 means f/1/4 , so f/1/4 will of
course be bigger than f/1/16. Most lenses produce the sharpest pictures
between f/5.6 and f/8.
Lens speed
Lens speed refers to how much light can go through the lens.
Lens speed can be categorized into 2 (two) different characteristics:
Fast lens: a lens that allows a relatively great amount of light to enter the
camera. Studio zoom lenses will mostly open up to f/1.6 which is fast
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enough to make the camera work in low-light conditions.
Optical Characteristics of Lenses (5/8)
Slow lens: a lens that transmits a small amount of light at the maximum
iris opening.
Remote iris control
Remote iris control enables the aperture to be controlled by the
video operator (VO) from camera control unit (CCU) so VO can perform
continuous light adjustment in order to maintain the picture quality.
Auto-iris switch
Most cameras, especially ENG/ EFP and consumer camcorders,
can be switched from manual to the auto-iris mode. For example the
switch takes place when camera takes place of a woman wearing bright
yellow/ white hat in sunlight. The auto-iris switch will automatically adjust
by overexposed whether the face of the woman or the hat.
In order to avoid handling an extreme contrast, the ENG/ EFP
cameras would do ND (Neutral Density) filters that would lower the
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extreme brightness .
Optical Characteristics of Lenses (6/8)
Depth of field
Depth of field is the range in which the objects are seen focus while other
object will be out of focus.
Operationally, the depth of field depends on the coordination of 3 (three)
factors: (1) the focal length of the lens, (2) the aperture (lens opening),
and (3) the distance between the camera and the object.
Focal length
It is the most influential on the depth of field.
In explaining this, wide-angle zoom position/ zoom out (short-focallength) would have a great depth of field.
Narrow-angle zoom position/ zoom in (long-focal-length) would have a
shallow depth of field.
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Optical Characteristics of Lenses (7/8)
For example, when taking the image of a fast moving vehicle, should it be
zoom out or zoom in?
The answer is zoom out because first, the zoom out will give clear view to
the viewer what is really going on; and second, the resulting great depth of
field will keep all shots in focus.
Aperture
Large apertures cause a shallow depth of field while small apertures
cause a large depth of field. The rule for aperture is large f-stop numbers
(such as f/16 or f/22) contribute to a great depth of field, small f-stop
numbers (f/1.7 or f/2) contribute to a shallow depth of field.
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Optical Characteristics of Lenses (8/8)
Camera-to-object distance
The farther the camera is from the object the greater the depth of
field. If the camera is focused on an object relatively far away from the
camera then there will be great depth of field and there is no difficulty for
the camera in adjusting focus.
For short, it can be said that the depth of field is shallow when the
camera uses close ups and low light levels. The depth of field is great
when the camera uses long shots and high light levels.
Operational Control
There are 2 (two) basic controls to operate a zoom lens: (1) the
zoom lens that lets to obtain zoom out to a wide shot or zoom in to a close
up, and (2) the focus control that slides the lens elements that lie close to
the front of the zoom lens back and forth until the image or a specific part
of the image the zoom lens delivers is sharp.
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Operational Control (1/2)
To operate a zoom lens, there are 2 (two) basic controls required: (1)
zoom control, the system that allows zoom out to a wide shot or zoom in
to a close-up, and (2) focus control, the equipment that slides the lens
elements to the front of the zoom lens back and forth until the sharp
image is obtained.
Zoom control
There are 2 (two) characteristics of zoom control;
The automatic zoom control: the required zoom where the image to be
executed is on very smooth zoom;
The manual zoom control: the required zoom where the image to be
executed is extremely fast zoom and the focal length of the zoom lens
must be changed with great speed.
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Operational Control (2/2)
Focus control
This focus control activates the focus mechanism in a zoom lens. There
are 2 (two) types of focus control:
 Servo focus control is the type of camera that the lenses can be set to
keep it focus during rehearsed camera or subject movements.
 Auto focus is the type of camera that the camera itself does not know
exactly on which object in the frame to focus.
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