Saturday, February 11, 2006

Detailed Description About Video Cameras

The video camera is a kind of transducer, which produces electrical energy from light energy. I.e., the input to the video camera is light energy and this light energy is converted into electrical signals. Video converting the complete spectrum of visible light into electrical frequencies.

There are two basic types of video cameras: monochrome (Black and White) and color. Monochrome cameras are lower in price, but color is more realistic. Both have advantages and both are desirable. By using both types we can intersperse black and while pictures with color to produce special effects. But, as far as camera features are concerned, black and while cameras can have features found in the most expensive color cameras monochrome cameras require less light than color cameras and operate with battery power. They do not have as many adjustments as color cameras, hence they are easier to use.

The video camera not only converts the light reflected from a scene into an analogous video voltage, but it also supplies the necessary sync and blanking pulses to go along with it. In short, the video camera produces the equivalent of an NTSC (National Television Standards Committee) signal, the same sort of signal that is generated by a television broadcasting station.

There is one exception, though. At the TV broadcasting station the composite video signal is loaded on to a carrier wave so as to be able to cover the distance between the station and all the receivers tuned to it. The composite video signal, recorded on videotape by the VCR accompanying the camera, can be inserted into the in-home VCR for reproduction on the television screen. But that missing factor, the carrier wave, must be introduced. This is handled by the converter section of the VCR, supplying a carrier wave whose frequency is that of either channel 3 or channel 4. Thus the composite video signal, now complete with a carrier, can be sent into the TV receiver via its antenna terminals. All that is required of the TV set is that it’s tuner be adjusted to the frequency of the carrier that is, either the frequency of channel 3 or channel 4, whichever frequency is used by the converter

A video camera can be used indoors or out. For in-home use power for operating the camera can be obtained from the AC power line by using an adaptor or the battery pack, as an additional piece of equipment. The amount of power used by a camera is least when various camera functions are manually operated. It takes battery power to make use of cameras automatic features. Thus a camera could need 7.6 watts approximately with its auto focus in the manual position. The camera used in this project work is designed to operate 12V DC.

The trend in video camera design is to produce cameras that are as lightweight and as compact as possible. The camera used in this project work is known as Board camera and the weight of this camera is less than 200 grams. The details of the Board camera collected from Internet, the details along with the picture is as follows










The above is the photograph of the actual camera used in this project work .

We may find references to cameras as being all solid state, often neglecting to add that the camera does contain a camera tube, known as pickup tube. These tubes are identified by various names selected by camera manufactures, including Saticon, Newvicon, Plumbicon, Trinicon, Univicon, Viconf, and Vidicon. Unless the camera manufacturer has its own picture tube manufacturing division, it is quite likely that the various camera tube types are supplied by the same source.

CAMERA OPTICS

As in motion picture film cameras, the optics represent the most important part of the camera and this includes the lens or the lens system and the viewfinder.

FOCAL LENGTH

In a film camera focal length is the distance from the optical center of the lens to the film. In a video camera it is the distance between the optical center of the lens and the target area of the picture tube. A short focal length means light inside the camera, whether film or video, has a shorter distance to travel, and so less light is lost, hence the attractiveness of keeping the focal length as short as possible. Focal length is measured in millimeters (mm) and is supplied as a range.

OPERATING POWER

The operating power requirements of a video camera are approximately 6 to 8.5 watts DC. This doesn’t sound like much and it is not if the camera is being used indoors and is connected to an outlet supplying 230 volts AC, changed to 12 volts DC by a converter. But it is another matter if the camera is being operated outdoors and must rely on batteries for power. Under such conditions a camera having the smallest power requirement would be the most desirable one if this were the only feature being considered.

The video camera used in our project work is arranged over a revolving disk, naturally 12V battery pack must be provided over the disk to drive the camera.

LENSES

There are two types of lenses: fixed and adjustable. A fixed lens is so-named since its focal length cannot be changed. This is the type of lens used on inexpensive film cameras. Its angle of view is constant and if you want to get closer to a scene or farther away, you can only do so by moving the camera, probably by walking with it.

ZOOM LENS

The zoom lens is an adjustable type. Since its focal length is variable you can use this lens to make the angle of view wider or narrower, with in the limits of the lens. This means you can make a scene seem to come closer or farther away without moving the camera physically but just by making a lens adjustment.

However, the fact that a lens is a zoom type does not automatically make it a better quality lens. Nor is the focal length determined by whether the camera is color or monochrome. Thus you might get a black-and-white camera having a zoom lens with a greater focal length range than a color camera.

FOCUSING.

The purpose of focusing is to get as clear and sharp an image as possible. In focusing the lens is adjusted for the best image clarity. The region behind and in front of the subject that is also in focus is called depth of focus or field of focus.

Focusing can be done manually, semi automatically, and completely automatically. There is also a type of focusing, known as macro focus, in which the subject is brought very close to the camera lens.

MANUAL FOCUS

Manual focusing, also called mechanical focusing, is an arrangement in which a focusing control, mounted on the camera can be rotated clockwise or counter clockwise. It is supplied with distances marked on the control, which is a ring positioned near the lens. With manual focusing it is necessary to adjust the focusing ring to correspond to the distance from the subject to the lens.

AUTO FOCUS

In the auto focus mode simply point the camera at the subject and start shooting. The focus will be continuously adjusted as the subject-to-camera distance changes, as long as the subject remains in the center of the frame.
There are certain conditions under which auto focus does not work well. You may find it difficult to get proper focus with objects that reflect strong light, such as glass or metal or objects made of black wool or black velvet, or objects that coexist far and near. For such shooting conditions set the focus auto/manual control to its manual focusing position.
Auto focusing is easy and so there is a natural tendency to rely on it and to let the camera do all the work.

SEMI AUTOMATIC FOCUSING

With this system the camera focuses on the subject. But as the subject moves it is necessary to depress a focusing button to refocus. This becomes a series of focusing steps.

LIGHTING

As a general rule as you increase the amount to light on the subject being video graphed, the quality of the picture recorded on the tape becomes better. This is not usually a problem outdoors, except when shooting around nightfall. In the home you may need floodlights, even with window shades pulled up. It may sound like disadvantages to need to use artificial lighting, but since you have control of the light, something you do not have outdoors, you can get some dramatic and unusual effects.

You will need to experiment with lighting and you may find it helpful to buy floodlights and reflectors similar to those used in photography consider also that lighting is often best when done from front and rear. And a caution: never point your camera directly at the light since this could damage the picture tube in the camera.
LUX

The lux is the international system unit of illumination and equals one lumen per square meter. The plural of this word is luxes or luces, but is commonly ignored. Thus, the singular form, lux, is now used with all numbers, such as 1 lux, 50 lux, etc., this is industry procedure and is followed in this report. The abbreviated symbol for lux is lx.

CAMERA SENSITIVITY

The sensitivity of a camera is expressed in lux units and may be indicated in the cameras spec sheet. For a camera using an f1.5 lens the sensitivity could 75 lux with the cameras sensitivity switch set in its high position.

Sensitivity figures are sometimes specified as a range. Thus a camera could have sensitivity from 75 lux to 100,000-lux illumination. The camera could also have a high gain switch to permit using the camera under low light conditions. The high gain switch can be activated to prevent underexposure. Some cameras also feature a back light control to be used when the overall brightness of the scene would otherwise cause the subject to be underexposed.

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