How Camcorders Work: Part II – So, How Does a Camcorder Work Anyway?
In part one of our camcorder series we discussed the basics of analog, digital camcorders, and charge-coupled devices [CCD]. We’ll dig a bit deeper into the CCD and data conversion in this article.
Camcorders and digital still cameras take pictures using CCDs. However, since camcorders produce moving pictures the CCDs in digital camcorders are not the same as those in digital cameras. A camcorder CCD has to take many pictures every second to create video signal. The camera combines the signal to give the viewer the impression of movement.
A television basically ‘paints’ images from the top down. It works in horizontal lines across the screen. The TV paints every other line in one pass. On the second pass it paints the other lines. Each of these passes is referred to as a ‘field’. Therefore, when a camcorder creates a video signal it captures a video frame from the CCD and records it as two fields.
The CCD transfers photosite charges to another sensor layer behind the image sensor. Every video field transfers to the second layer. The second layer transmits the electric charges one by one at each photosite. In analog camcorders the signal goes to the VCR and records as magnetic patterns on videotape. As the second layer transmits video signal the first layer refreshes and captures another image.
Digital camcorders work the same way. However, at the final stage an analog-to-digital conversion occurs. An analog-to-digital convertor samples analog-signal and converts the data into data bytes. These data bytes are 1s and 0s. The camcorder then records these data bytes to a storage medium. Typical storage mediums are tape, DVD, or hard disk. Most manufacturers produce digital camcorders to use tape. Tape is less expensive and records binary code instead
of magnetic patterns.
Progressive digital camcorders record video as a still frame. The frame is broken up into two fields when the video outputs as an analog signal. Interlaced digital camcorders record a single frame as two fields much like analog camcorders do.
Record a Clear Picture
To record a clear picture you need the ability to adjust lens focus. You must move the lens so that it aims the beams of light from the object on the CCD. You’ll move your lens in and out to focus light. Unfortunately, most users must move around with their cams, shoot from different distances. This makes constant refocusing extremely challenging. Fortunately, most camcorders come with an autofocus feature built-in. This is usually an infrared beam that bounces off
objects and returns the beam to camcorder sensor.
The object’s distance is processed by calculating how long it takes the beam to bounce and return. This is multiplied by the speed of light and divided by two. Two is used because the distance is traveled twice. A small motor then moves the
lens focusing in on objects at the distance calculation. This is usually effective but sometimes you must override the autofocus.
Zoom Lenses
Most camcorders also come equipped with a zoom lens. A zoom lens magnifies an image by increasing the focal length of the lens. [The focal length is the distance between the lens and the CCD]. An optical zoom is a single lens device that allows you two change the focal length. This allows you to move from one magnification to a closer magnification. The zoom range gives you the minimum and maximum magnification of the device.
Most camcorders have an attached motor that adjusts the zoom lenses for you. This makes the zoom function easier to use. They normally adjust with a simple toggle control on the cam’s grip. The toggle control allows you to operate the
zoom without using your free hand. The motor also adjust the lens at a steady speed. This makes zooming more fluid.
Some camcorders have a digital zoom. A digital zoom magnifies pixels and stabilizes them. However, you sacrifice resolution quality because only a portion of the available photosites gets used. This happens because a digital zoom only captures a part of the total picture versus the whole picture. The loss in resolution makes for a fuzzy image.
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