TELEVISION CAMERA OPTICS

LEARNING OBJECTIVE: Identify the optics of a television camera.

You were introduced to the functions of camera lenses in Chapter 11. The lenses and the associated optics for television cameras (save viewfinder) operate in the same manner as still photography, but we will cover them briefly as they apply to the television medium.

VIEWFINDER

The viewfinder on an ENG camera is a relatively small television screen (1.5 inches in diameter), while a studio camera viewfinder is larger (3 to 9 inches in diameter). They both produce high resolution black-and-white images. The television screen on an ENG camera is shielded from outside reflections by a flexible rubber eyepiece that adjusts to the operator's eye. In that rubber eyepiece, there is an adjustable lens for you to focus since the eye is placed within an inch or two of the screen. The studio viewfinder uses a hood to shade the television screen from overhead studio lights.

Within the ENG camera viewfinder, there are a number of control lights or displays that indicate the status of certain camera functions. Most viewfinders automatically display information on tape status, battery condition, tally/record light and low-light level indicator. The viewfinders display, on command, color bars, patterns, white/black balance setup cursor and camera registration. All camera viewfinders are black-and-white.

In some camera models you may use the viewfinder as a playback monitor for the VCR. The advantage of this feature is that you do not need additional equipment to set up the camera. However, some video camera manufacturers are discontinuing this feature because today's cameras are more reliable and recorders have indicators to let you know when you are recording.

LENS

The lens selects a certain field of view and produces a small, clear optical image of this view. The lens and certain attachments are sometimes called the external optical system.

When you work with video camera lenses, you concern yourself with the following four areas: l Focal length l Focus l f/stop c Depth of field

Focal Length

As you learned in Chapter 11, focal length is the distance from the optical center of the lens (which is not always its physical center) to the point where the image, as seen by the lens, is in focus.

Portable television cameras have a zoom, or variable focal-length lens (fig. 14-8), that allows you to select fields of view at different distances from the camera without moving the camera. It allows you to change the focal length of the lens from long to short or from short to long in one continuous operation. A complicated series of lenses interact to keep the object in focus at all times during the zooming process. "Zooming in" is the gradual changing of the lens from a wide-angle lens to a narrow-angle lens. On the television screen, a zoom in appears as though the camera is moving smoothly toward the object. "Zooming out" is the changing of the lens from a close-up to a distant shot and it will appear that the camera is moving away.

The degree to which you can change the focal length of a zoom lens is the zoom range of your lens. The range is often given in a ratio, such as a 10:1 zoom range. This means you can increase your focal length 10 times. Some cameras have a "times two function," which allows you to double the focal length at any point in the zoom, thus making the maximum 20:1 for the above example.

You can control the speed of your zoom either manually or by using a zoom servo. These features are covered in the following text.

MANUAL ZOOM CONTROL. - The manual zoom control on ENG cameras is a small rod extending from the zoom ring. To zoom in or out, turn the zoom rod clockwise or counterclockwise. It takes some skill and practice to accomplish smooth zooms with the manual control.

ZOOM SERVO. - A zoom servo is nothing more than a small motor controlled by a lever. The distance the lever is depressed determines the speed of the zoom typically from 2.5 to 20 seconds. The lever is called the zoom selection or T/W switch - T stands for telephoto and W for wide angle.

There are several advantages to the zoom 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 zoom servo also frees the left hand to operate the manual focus and aperture controls.

Figure 14-8. - Zoom lens.

You must be aware of two disadvantages of the zoom servo. Although relatively quiet, some zoom servo motors emit a humming noise that is picked up by the camera-mounted microphone. Additionally, the motor uses power provided by the camera battery.

FOCUS CONTROL. - The focus control is usually a rubber-covered ring on the zoom lens. To operate it, you rotate the focus ring either clockwise or counterclockwise while looking in the viewfinder to determine if the picture is in focus.

Focus

Two methods of setting the focus on a zoom lens are used. One, called zoom focus, is done by zooming all the way in and setting the focus, then zooming out to the desired focal length. Once this is done, everything in the depth of field will remain in focus, including the object focused on, provided the distance between it and the camera does not change.

Another focusing method is called rack focus. This is nothing more than your setting the focus on something in the field of view. When you do this, only that object and other objects at the same distance will remain in focus as long as the distance between them and the camera does not change.

You should rack focus when there is not enough time to zoom focus. However, there are times when the effects of a rack focus are desirable, such as when the viewer's attention is directed toward something in the foreground and you want to lead him to another object. You can do this by changing the focus to bring the other object into sharp focus while the first object goes out of focus.

f/Stop

As noted earlier, the camera pickup tube will operate properly only within a certain range of light intensity. If too much or too little light falls on the pickup tube, the picture quality will suffer.

Since you will use the camera both indoors and outdoors, you must compensate for extreme differences in light levels. The lens diaphragm, or iris, is used to control the amount of light that enters the lens and the camera by enlarging or reducing the aperture. The f/stops indicate the size of the lens (diaphragm) opening.

Figure 14-9. - The talent, camera operator and floor manager on the set of Navy News This Week (now titled Navy/Marine Corps News).

The lower the f/stop number, the wider the lens opening. When you zoom in, the lens will require more light, a wider opening and a lower f/stop number.

Most television cameras have an automatic iris that allows you to devote your attention to other important aspects of videography, such as framing and composition. Although the automatic iris seems ideal for ENG assignments, it does not always work to your advantage. With fairly even illumination, the auto iris closes down when it sees an extremely bright area in a scene or opens up when it senses a large, dark area. You can avoid this by switching to the manual iris control.

Depth of Field

It is important for you to know that f/stops do more than just determine the amount of light entering the camera. They also affect the depth of field.

As in still photography, a large diaphragm opening (small f/stop number) decreases the depth of field, and a small diaphragm opening (large f/stop number) increases it. The same rules apply when you move the camera. A great depth of field makes it easy for you to keep the subject in focus while moving short distances, whereas a shallow depth of field makes it impossible for you to move without getting the subject out of focus.