VideoPreservation Website

Chapter 4

The Video Camera

CAMERA TUBES

The electronic or VIDEO CAMERA is similar to any other camera in that light reflected from an image is focused by a lens onto a plane inside the camera. Unlike the film camera, the video camera contains a CAMERA TUBE which processes the image. Types and sizes of video cameras vary greatly, because they must be designed for a variety of different applications. The video camera's use determines the sophistication of the design, the cost and the type of camera tube.

Originally, camera tubes were as large as 3 or 4 inches in diameter and required incredible amounts of light to produce good pictures. The evolution of video technology has provided us with the inexpensive and versatile VIDICON TUBE, characterized by good light sensitivity, small size and excellent picture sharpness. Although there are other kinds of tubes far superior to the Vidicon, some tubes cost 10 to 20 times as much as the vi d icon's relatively low cost of $70 to $120.

The camera tube plays a major role in determining the light sensitivity of the camera, the sharpness of the picture and whether or not the image will be reproduced in black-and-white (b&w) or color. B&W cameras contain only 1 tube, but color cameras may have as many as 3 or 4 tubes.

The Vidicon is the standard tube used with nearly all nonbroadcast closed circuit small format video gear. Variations on the V idicon include the TIVICON, an extremely low light level tube that uses silicon diodes; and the NEWVI CO N, a sophisticated low light level tube produced by Panasonic.

One of the limitations of the Vidicon is its inability to deal with very low light level scenes. At low light levels, the image quality will be grainy and an annoying "lag" or ghosting effect will be apparent. Improved circuitry used in post-1973 cameras has allowed b&w cameras to produce fairly good pictures in less than 20 footcandles of light—the equivalent of average household room lighting. A FOOTCANDLE is that amount of illumination falling on a surface one foot away from one candle.

The more expensive Tivicon Tube will produce good pictures in 2 footcandles (a very dark room) and the Newvicon functions as an in-between option with some of the low light sensitivity of the Tivicon but costs less and performs better in regular light situations. The Panasonic Newvicon is highly resistant to burns and typical vidicon tube lag and doesn't turn the picture black on bright background shots. For production purposes, the Newvicon is far superior to the Tivicon, Most standard b&w cameras can be modified to accept the Tivicon or Newvicon tubes at extra cost.

Another common camera tube is the Philip's PLUMBICON (lead oxide) Tube, the standard of the Broadcast TV industry. It is an excellent, sophisticated, low light, high resolution tube and is used in most color broadcast TV cameras. Other high-performance broadcast quality color tubes are the CHALN ICON tube, a cadmium selenide design, or the SATICON tube, a tin/oxide/selenium—arsenic/tellurium design. All three of these tubes are available in the 2/3-inch size for use in portable cameras.

The tube's size greatly affects the resolution of the picture. The most common tube size has a 2/3-inch tube faceplate diameter and could be likened to the relative image size as referred to in 8mm or 16mm film. The larger the tube faceplate size, the larger the picture area and the better the picture quality of the image. The 2/3-inch Vidicon is commonly called a SEPARATE MESH TUBE, because it contains a separate screen inside the tube which increases picture sharpness and reduces image lag.

Electrostatic Focus Tubes

Older cameras such as the Sony A VC-3400 or AVC-3200 series utilize the conventional vidicon called the MAGNETIC FOCUS MAGNETIC DEFLECTION type which requires an external focusing assembly to focus the electron beam on the target plate. This external assembly, or focusing coil, needs extra DC power.

Inside the Vidicon Tube

The light sensitive element of the Vidicon, called the target, consists of a light sensitive transparent electrical conducting film on the inner surface of the faceplate and a photoconducting layer immediately behind the electron gun side. The photoconducting layer changes resistance in inverse proportion to the brightness of the light falling on the target plate. That is, a bright spot hitting the target plate results in less resistance and a higher voltage when the beam sweeps across the spot. Less light results in a lower voltage on the target plate.

The later model cameras such as the Sony AVC3450 and AVC-3250 & 3260 series cameras, and most b&w Panasonic cameras utilize the ELECTROSTATIC FOCUS MAGNETIC DEFLECTION Vidicon assembly which has internal electrodes within the Vidicon tube itself that focuses the beam. This eliminates the need for the heavy focusing coil which then greatly reduces the power consumption, weight and size of the camera. Some cameras are now approximately the size of a pocket calculator.

The camera tube is basically a TV set in reverse:

Light is reflected from image (A) focused by lens (B) on target plate (C). The target is scanned by the electron beam (D) produced by the tube and converted into electrical information or voltage and amplified (E). Finally, electrical information passes by wire to the picture tube or cathode ray tube (CRT) in the TV monitor (F). The CRT scans the face of the TV tube in the monitor in step with the electronic information supplied by the camera (G). The image is displayed on the light-sensitive face of the CRT, converting electrical information back into light information again.

CCD Cameras

The camera tube is the main limitation of the camera's size. With INTEGRATED CIRCUITS (IC's) most of the camera electronics can be reduced to a few square inches. RCA sells several b&w cameras that have eliminated the tube entirely and instead use what is called a CHARGE COUPLED DEVICE (CCD). These devices are basically composed of thousands of tiny light sensitive circuit arrays in a grid which can scan a picture. Like other solid state devices, CCD cameras use minimal power, generate little heat and are ultra-reliable and compact.

CCD cameras can include a light-amplifying circuit on the faceplate to greatly improve the camera's low light ability. A Fairchild CCD camera is available that can function in 125 millionth of a footcandle! Noise levels (undesirable picture grain) can be reduced significantly because of the integrated video amplifier design so that contrast ratios of 500 to 1 (similar to film) can be achieved. Soon, the resolving power of the CCD camera will far exceed the best lenses, and the video camera will be 98% lens and 2% electronics. Then we will need to invent electronic lenses. CCD designs currently are being integrated into other video-system components.

TYPES OF CAMERAS

As we've said, cameras are designed to serve a wide variety of purposes. The simplest type of camera consists merely of a body and lens. This is the common surveillance type, usually found inconspicuously guarding book stores, supermarkets and liquor stores in a "1984ish" manner. In order to be usable for production purposes, the camera really needs an electronic viewfinder so you can see the picture you want the camera to shoot. Otherwise you must try to aim the camera by watching it on a monitor, which is somewhat difficu It.

Video camera viewfinders are electronic and function like a single-lens reflex camera, in the sense that you are able to see almost exactly what the camera tube sees. The electronic viewfinder is just a miniatu re TV monitor mounted on the side or top of the camera.

Generally, nonsurveillance video cameras fall into 2 basic categories—portable and studio R non-portable) cameras. Designed to operate on battery (DC) power, portable cameras are lightweight and compact but offer few external adjustments. On the other hand, studio cameras are heavier and bulkier, but offer lots of external adjustments and large viewfinders.

Video Camera Control

The quality of a video program is only as good as the picture the camera puts out. Proper lighting and camera adjustment are essential to a quality video production. All video cameras have adjustment features that can be used to optimize picture quality; some are controllable directly by the camera operator, and others accessible only by tak ing off the camera housing. Unless you have some background in electronics and/or access to the particular maintenance manual for a specific camera, equipment should not be disassembled. Otherwise, the camera may become even further misadjusted or damaged and require expensive repair.

Internally Controlled Cameras

Some cameras have no external adjustment controls, but have had their electronics preset at the factory for the average shooting requirements. Most hand-held portable b&w cameras are of this type. Typical internally controlled automatic cameras are the low-cost studio or nonportable video cameras. An example is the Sony AVC-3000 and AVC-3200 series cameras-3000, 3200, 3210, 3250, 3260, 3400 and 3450. These studio cameras have detachable viewfinders and are good rugged basic b&w cameras. They usually are purchased in package form which includes Zoom lens, tripod, viewfinder, microphone and carrying case.

Sony 3250 & 3260

Side View of Internally Controlled Studio Camera

These controls affect the VIEWFINDER ONLY.

They do not affect the picture that is being recorded. These controls are like those on any standard TV set.

Camera Controls

1. VIDEO OUT—The picture is transferred from the camera to the VTR or monitor by means of this plug. Connect the camera coaxial cable (RGC-15)---the one with the metal plugs on each end—from the camera to the VTR or the Monitor. Older model cameras, (AVC-3200 and AVC-3210), allow you to go directly to the VHF terminals on a TV set from the VIDEO/ RF plug. Make sure you place the VlDEO/RF switch in the RF position. See Chapter 8, RF Units—TV Monitor,

2. POWER SWITCH—Turns the camera on and off.

3. EXTERNAL SYNC/VIDEO—Y ou may use the 6-Pin plug to connect the camera to most Sony 1/2-inch VTR s, but this is not recommended. Instead, use the camera coaxial cable. The 6-Pin cable with this plug is used mainly to connect the camera to a multiple camera switcher and SPECIAL EFFECTS GENERATOR (SEG).

4. LIGHT LEVEL SWITCH—This very handy control allows the camera to be used in low-light situations, although the picture will lose some quality. The low-light mode will allow the camera to work in as little as 1.5 footcandles!

5. SYNC SELECTOR—Use INT (internal) SYNC if this is the only camera to be used. Use EXT (external) SYNC if several cameras are to be used and/or if a separate sync generator is being used. In the latter case, the 6-Pin cable is also required.

6. PILOT LAMP—signals that the camera is ON!

7. PEDESTAL LEVEL CONTROL—Located underneath the camera, this control is used to match or balance the camera pictures together when using several cameras at once. The pedestal control will affect the shades of gray and contrast levels of the picture.

Evaluation of the AVC-3250 & AVC-3260 Cameras

Both of these models are excellent b&w cameras. Their resolution is very good-500 lines at the center in the HIGH LIGHT MODE and 450 lines in the LOW LIGHT MODE. Both cameras are very stable, dependable and are completely solid-state, except for the Vidicon tube. The difference between the 3250 and the 3260 is that

the 3260 has 2:1 INTER LACE SYNC which is essential for editing. This feature is well worth the extra $100 if this is your main or only b&w camera, or if you intend to edit the pictures. The DX designation refers to the complete studio ensemble which includes carrying case, microphone, zoom lens and viewfinder.

Typical Externally Controlled Studio Camera—The Panasonic WV-361P

Panasonic has an excellent reputation for low and moderate cost studio cameras—perhaps the best. A variety of cameras are offered with the WV-361 P being one of the top of the line b&w model which features high performance and picture resolution, very good low light sensitivity and just about every accessory possible.

Camera Features:

• 2/3-inch separate mesh vidicon

• B ig 6-inch diagonally measured viewfinder   • Plug-in 2:1 interlace sync board—optional WJ-120

• Viewfinder also functions as a playback monitor • Built-in tally, intercom and headphone connections

• Picture resolution of 550 lines at center   • Integrated tally light

• Automatic light control compensation of 5000:1 •Operates on internal or external sync -Automatic/manual target control   •C-mount lens

• Image blur and ghosting eliminated   -Will operate in as little as 2 footcandles of light

1. FOCUS CONTROL—This control adjusts the electronic focus of the vidicon tube. The lens focus, optical focus, target and beam must be correctly set first.

2. BEAM CONTROL—This control adjusts the electron beam current inside the camera tube. Turn the control until the picture washes out and then returns to good quality black and whites. Excessive contrast will reduce picture sharpness.

3. AUTO/MANUAL TARGET CONTROL—This control adjusts the sensitivity of the camera tube target plate. This circuit is self-adjusting to a great extent, but for maximum sharpness, turn the control until the picture appears and then stop. Increasing the target voltage will produce greater picture contrast but will prematurely wear out the tube and cause greater image lag. It is probably best left in the AUTO mode.

4. ZOOM LENS—A variety of C-mount fixed focus or zoom lenses can be used.

Camera Rear Control Panel

1. TALLY LIGHT—Indicates to the actors that the camera is "on the air."

2. HORIZONTAL HOLD—Adjusts the horizontal hold for the viewfinder.

3. MONITOR SELECT—A 4 position switch that allows the camera viewfinder to function as a VTR recording monitor and a VTR playback monitor when used with a special connection to a VTR 8-PIN and as a camera monitor or a line view monitor when used with an SEG.

4. POWER/VOLUME—Turns the camera on and controls the sound level in the headphones—for audio monitoring when 361P camera is connected to VTR through special cable.

5. PI LOT LAMP—Indicates the camera is ON!

6. HEADPHONE JACK—Use for monitoring VTR playback with special cable.

7. INTERCOM JACK—Plug a 2-way intercom headset in here. NOTE: The camera must be connected to an external intercom system and SEG with a 10-Pin cable. See page 48 —Multiple Camera System Connections.

NOTE: On a remote shoot, the 361P can be used as a video and sound playback monitor with any VTR that has an 8-Pin connector. This eliminates the need to carry along a large TV monitor. You will need the special 6-Pin to 8-Pin connector cable however.

8. OPTICAL FOCUS CONTROL—This control actually moves the camera tube forward and backward relative to the lens. It is the equivalent of moving the film plane inside a film camera. To properly set, first focus the lens on a subject at infinity (a distance over 50 feet away), then turn the OPTICAL FOCUS control until the picture is sharp. Once the subject has been focused, the lens should be able to FOLLOW FOCUS—stay sharp as the lens is zoomed back and forth on the subject.

NOTE: The subject cannot change his camera-to-subject distance or refocusing will be necessary. The optical focus can be used for extreme close up shots of an object, even with a zoom lens, but the optical focus will have to be reset for the correct follow focus again.

9. REAR ZOOM CONTROL—This controls the optional rear zoom lens which is a very nice feature to have, but crank type zooms are much smoother than push rod types.

10. SYNC CONTROL—Set for INTernal sync if this is the only camera, or EXTernal sync if using an external sync generator and/or SEG.

11. CONTRAST CONTROL—Adjusts contrast only on the camera viewfinder.

12. BRIGHTNESS CONTROL—Adjusts the brightness only on the camera viewfinder.

13. VERTICAL HO LD—Adjusts the vertical hold only on the viewfinder.

Camera Bottom Connections

1. POWER CORD—Plug into 120 volts AC.

2. 10-PIN CONNECTOR—Use with a multiple camera system—supplies Video Out, Horizontal and Vertical Sync, Intercom, Tally, and Video Return to camera.

3. VIDEO OUTPUT CONNECTOR—A UHF plug used to take VIDEO out of the camera to the VTR or Monitor. Use this plug with a single-camera system.

4. VTR CONNECTOR—A 6-Pin plug used for a special cable connection to the 8-Pin plug on VTR. Use for video and audio playback monitoring.

5. TRIPOD MOUNT—For connecting camera to tripod.

6. ZOOM LENS SHAFT GUIDE—Guides zoom lens shaft control. WV-361P Set-Up Procedure

Read camera instruction manual thoroughly!

Step 1   Turn on the camera and open the lens.

Step 2   Adjust the lens iris for the best light.

Step 3   Focus the lens and adjust the viewfinder controls for the best picture.

Step 4   Adjust the OPTICAL FOCUS for the sharpest picture.

Step 5   Adjust the BEAM and TARGET controls for the best contrast.

Step 6   Adjust the ELECTRONIC FOCUS on the camera side for the sharpest picture.

   There are many kinds of video cameras, and   Most cameras will have most of the functions

   the control configurations of each model will vary   mentioned, although some controls may look dif-

   somewhat. The most common type of studio   ferent or may be preset and installed inside the

   black-and-white cameras used at the private, in-   camera housing. stitutional and professional level are mentioned.

NTSC Color System

Essentially, in the American system of TV, color video is just a few things added to b&w video, rather than a completely different process as it is in foreign TV systems. Because U.S. manufacturers initiated TV and had produced millions of b&w sets, they had to make the color system compatible with existing TV sets. Otherwise, we would need one TV set for b&w signals and one TV set for color. Unfortunately, having to work with a b&w-based system created restrictions on the development of the American color TV system. The rest of the world recognized the limitations of the American color system and instead designed more advanced and better TV systems for themselves.

The American TV System is officially called the 525-line NTSC System which stands for the NATIONAL TV STANDARDS COMMITTEE OF THE ELECTRONIC INDUSTRIES ASSOCIATION. However, it is often facetiously called Never the Same Color Twice by typically cynical TV engineers. Western Europe uses a 625-line system called PAL, and France, of course, had to have its own system called SECAM, which is also used by the Soviet Union. None of these systems are compatible and videotapes made in the USA will not play back on similar European videotape recorders and vice versa. There are special, very costly transfer processes for changing tapes from one standard to another although the Sony TRIDENT U-Matic VCRs, such as the VO-2630 recorder and the VO-2030 player, will play tapes made on the 3 different foreign standards through a special monitor (PVM-1850). The VO-2630 can record PAL and SECAM but not NTSC, nor can these VCRs transfer a tape from one format to another.

COLOR CAMERAS

The most delicate part of the color video system is the color camera, and it can often be more expensive than the VTR. A low-cost color camera for 1/2-inch or 3/4-inch VTRs will range from $1,000 to $5,000 as compared to $1,000 to $2,500 for the appropriate color VTR. The high price of the camera is due to the delicate nature of the color tube or tubes, the color processing circuitry and initial research and development costs.   -

The Color Process

Color in TV works through the ADDITIVE color process of combining red, green and blue to form any shade of color in the spectrum. Add red to blue and you have purple, combine green with red, and you produce yellow and orange; and add all 3 together and you get white—electronically. Video cameras sense through these 3 primary colors and combine them to produce all the colors.

In video, we started out in b&w only. So what is black-and-white TV? It's the full range of levels of grays—between black and white. Call that the GRAY SCALE.

Since the gray scale is really an indication of BR IGHTNESS, the technical folks decided to call it LUMINANCE.

B&W Gray Scale = Brightness = Luminance

If we must add color, we have 2 subdivisions—the shade of the color, called HUE: and the amount of color, called SATURATION or intensity.

HUE = shade of color, i.e., red or green

SATURATION = intensity of color, i.e.,

high saturation of red = bright red low saturation of red = dull red

If wecombine HUE and SATURATION together we get what's called CHROMA or CH ROMINANCE, which we can define as the overall value of the color. If we take away all chrominance information, we are left with our b&w gray scale.

Color video deals with these 2 basic components—the luminance information (brightness) and the chroma information (color). The best way to produce color is to use one tube for each primary color and one tube for the luminance. Thus we have a 4-tube color camera.

The Four Tube Camera

A special device called a BEAM SPLITTER PRISM breaks up the white light from the lens into the 3 separate colors for the color tubes in the camera. The individual color signals from the tubes are then mixed electronically by a MATRIX and added to the luminance signals generated by a separate luminance tube.

The Three Tube Camera

In this case the luminance is derived from the green color tube. The three- and four-tube systems produce superb color, especially when Plumbicon tubes are used. Most broadcast cameras in the $20,000 and higher range utilize the 3- or 4- Plumbicon tube approach. The drawbacks of such systems are: high cost and complexity, extra electronics and weight, and the necessity to have each tube perfectly lined up with others. This lining up process is called REGISTRATION. If the images sensed by each tube do not line up with each other, the image looks out of focus; has poor color; and will have red, green or blue outlines around it. Registering is a tricky adjustment, so cameras had to be simplified for nonbroadcast users.

The Two Tube Camera

Some low cost color cameras ($1,200 to $2,700) used the 2-tube system, but it has never become very popular. One tube delivers luminance information and one tube delivers chrominance information.

The single chrominance tube separates the red, green and blue by means of a COLOR DISSECTOR TUBE which uses tiny red, green and blue stripes near the target area to scan each color sequentially. Often this tube is referred to as a STRIPE FILTER TUBE. Still, we have registration problems and the need for extra space to house the 2 tubes and optical mirrors.

Akai and JVC portable cameras use 2-tube electrostatic focusing electromagnetic deflection-type Vidicons placed at right angles to each other. The white light is split into a green component which is processed by a green tube, and the remaining light is processed by a yellow (minus blue)filter in the red/blue tube.

These home color cameras are remarkably compact, lightweight and light sensitive. They will take a good picture in almost standard room illumination. Automatic internal circuitry and ingenious built-in view finder LIGHT-LEVEL INDICATORS insure perfect exposure control. The Hitachi VK-500 camera even incorporates a tiny built-in audio speaker in the electronic viewfinder for picture and sound playback through the camera. All these home color cameras are practical modular designs which allow later addition of optional accessories such as zoom lenses and electronic viewfinders to the basic model.

The Camera Control Unit or CCU

Since cameras are not only more complex but also require more internal controls, more external knobs and buttons, and more light than b&w cameras, some portable models require an auxiliary control box called the CCU or camera control unit. The CCU must always be plugged into the camera for the camera to work and thus represents an extra item that has to be carried along with the camera. The CCU usually contains color processing circuitry, the camera

output plugs and adjustments for setting the camera for the prevailing lighting conditions. Since both natural and artificial light have a pronounced effect on color, the camera must be properly adjusted so it will keep the whites white and not produce a brownish, bluish or yellow tint on everything. Choice of color film requires the same care. You must buy indoor or outdoor film, according to your lighting needs.