LENSES Pertemuan 5

Matakuliah : O0382 – Dasar-dasar Produksi Siaran TelevisiTahun : 2010

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 lensesStudio 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 rangeZoom 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 15x zoom range. 3

Types of Zoom Lenses (2/4)

Optical and digital zoom rangeAn 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 lensesIn 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 lensesThese 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 lensesThough consumer camcorder have zoom range of 10x to

18x the maximum wide-angle position is often not wide enough. Most camcorders have some sort of image stabilization. 5

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. 6

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 LengthFocal 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 wide-angle 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 position to maximum narrow-angle position.

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Optical Characteristics of Lenses (2/8)

Minimum object distance and macro positionMinimum 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 lensPresetting (calibrating) zoom lens is conducted when

automatic focus control is absent from the camera.

Light transmission: iris and f-stopIris 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 camera. 9

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 speedLens 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 enough to make the camera work in low-light conditions.

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Optical Characteristics of Lenses (5/8)Slow lens: a lens that transmits a small amount of light at the maximum iris opening.

Remote iris controlRemote 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 switchMost 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 extreme brightness .

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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-focal-length) 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 (6/8)

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.

ApertureLarge 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 ControlThere 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. 14

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 controlThere 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 controlThis 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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